Standardizing technical parameters and terms for abdominopelvic photon-counting CT: laying the groundwork for innovation and evidence sharing

Photon-counting detector CT (PCD-CT) is a new technology that has multiple diagnostic benefits including increased spatial resolution, iodine signal, and radiation dose efficiency, as well as multi-energy imaging capability, but which also has unique challenges in abdominal imaging. The purpose of this work is to summarize key features, technical parameters, and terms, which are common amongst current abdominopelvic PCD-CT systems and to propose standardized terminology (where none exists). In addition, user-selectable protocol parameters are highlighted to facilitate both scientific evaluation and early clinical adoption. Unique features of PCD-CT systems include photon-counting detectors themselves, energy thresholds and bins, and tube potential considerations for preserved spectral separation. Key parameters for describing different PCD-CT systems are reviewed and explained. While PCD-CT can generate multi-energy images like dual-energy CT, there are new types of images such as threshold images, energy bin images, and special spectral images. The standardized terms and concepts herein build upon prior interdisciplinary consensus and have been endorsed by the newly created Society of Abdominal Radiology Photon-counting CT Emerging Technology Commission.

Photon counting x-ray detectors as scatter probes

BACKGROUND

Direct conversion x-ray Photon Counting Detectors (PCD) are posed to play a vital role in future medical imaging devices such as Computed Tomography (CT) scanners. PCD are expected to improve current CT technology on several fronts, such as resolution, dose utilization, and spectral performance. However, they are not readily expected to improve the handling of object scatter, one of the major sources of image artifacts in CT technology.

PURPOSE

We explore a potential method for obtaining in-situ object scatter estimation using the same PCD array used in the x-ray imaging system, such as in computed tomography. This unexpected benefit of using PCD has the potential to improve the image quality by providing better input into the scatter estimation and correction algorithms used in image reconstruction.

METHODS

In CT scanners the primary method for rejecting scatter signal originating from the scanned object relies on placing anti-scatter grids (ASG) close to the detector plane. This remains the case when transitioning to using PCD instead of energy integration detectors in CT. However, the combination of PCD and ASG opens a possibility to use some of the unique properties of PCD, namely, very low noise and coincidence counters to obtain, in addition to the attenuation data, a simultaneous and instantaneous estimate of the scatter signal reaching every detector element. When a small air gap is introduced between the ASG and the detector surface, the scatter radiation with large angular distribution has a greater probability of producing charge sharing events that can be detected by a coincidence counter. In this work we demonstrate the feasibility of such an approach in a tabletop experiment using PCD detector that lacks coincidence counting capability, instead we use the spectral signature of split charge events as proxy to coincidence counting. For this purpose, we first demonstrate the spectral impact of ASG misalignment using the same experimental setup. In addition, we perform a separate tabletop scattering experiment from a narrow column of water that demonstrates another potential use of the low noise capabilities of PCDs.

RESULTS

We measured and quantified the high sensitivity of the spectral response to ASG alignment on the PCD detector pixel array, we found that the probability of energy misregistration of 60 keV photons can increase by up to a factor of 3 when the ASG is poorly aligned. We then leveraged these results to obtain an estimate on the expected increase in coincidence counts for a wide range of scatter-to-primary (SPR) ratio and find a good match with expectations from a geometric modeling of the system, where the expected increase in coincidences was of the order of the SPR. Finally, the low noise detector also allowed us to measure the real space scatter signal associated with the coherent molecular form factor of water, revealing the ring-shaped scatter signal with an energy dependent distribution that was well captured by calculation.

CONCLUSIONS

The advent of PCD detectors and their imminent use in commercial CT scanners opens new and exciting possibilities for utilizing PCD detectors in unexpected ways. In this proof-of-concept study, we showed how charge sharing, a spectral information degrading effect, can instead be used to obtain in-situ scatter estimation. We also demonstrated the PCD ability to perform extremely sensitive measurements using affordable benchtop setup for investigations normally reserved for synchrotron facilities.

Gadolinium K-edge angiography with a spectral photon counting CT in atherosclerotic rabbits

PURPOSE

The purpose of this study was to investigate the feasibility of gadolinium-K-edge-angiography (angio-Gd-K-edge) with gadolinium-based contrast agents (GBCAs) as obtained with spectral photon counting CT (SPCCT) in atherosclerotic rabbits.

MATERIALS AND METHODS

Seven atherosclerotic rabbits underwent angio-SPCCT acquisitions with two GBCAs, with similar intravenous injection protocol. Conventional and angio-Gd-K-edge images were reconstructed with the same parameters. Regions of interest were traced in different locations of the aorta and its branches. Hounsfield unit values, Gd concentrations, signal-to-noise (SNR) and contrast-to-noise (CNR) were calculated and compared. The maximum diameter and the diameter of the aorta in regard to atherosclerotic plaques were measured by two observers. Images were subjectively evaluated regarding vessels' enhancement, artefacts, border sharpness and overall image quality.

RESULTS

In the analyzable six rabbits, Gd-K-edge allowed visualization of target vessels and no other structures. HU values and Gd concentrations were greatest in the largest artery (descending aorta, 5.6 ± 0.8 [SD] mm), and lowest in the smallest (renal arteries, 2.1 ± 0.3 mm). While greater for conventional images, CNR and SNR were satisfactory for both images (all P < 0.001). For one observer there were no statistically significant differences in either maximum or plaque-diameters (P = 0.45 and all P > 0.05 in post-hoc analysis, respectively). For the second observer, there were no significant differences for images reconstructed with the same parameters (all P < 0.05). All subjective criteria scored higher for conventional images compared to K-edge (all P < 0.01), with the highest scores for enhancement (4.3-4.4 vs. 3.1-3.4).

CONCLUSION

With SPCCT, angio-Gd-K-edge after injection of GBCAs in atherosclerotic rabbits is feasible and allows for angiography-like visualization of small arteries and for the reliable measurement of their diameters.

Virtual monochromatic images for coronary artery imaging with a spectral photon-counting CT in comparison to dual-layer CT systems: a phantom and a preliminary human study

OBJECTIVES

To evaluate the quality of virtual monochromatic images (VMIs) from spectral photon-counting CT (SPCCT) and two energy-integrating detector dual-energy CT (EID-DECT) scanners from the same manufacturer, for the coronary lumen.

METHODS

A 21-cm section of the Mercury v4.0 phantom was scanned using a cardiac CT protocol. VMIs from 40 to 90 keV were reconstructed using high-resolution (HR) parameters for EID-DECT and SPCCT (CB and HRB kernels at 0.67 mm slice thickness, respectively). Ultra-high-resolution (UHR) parameters were used in addition to SPCCT (detailed-2 kernel, 0.43 mm slice thickness). Noise-power-spectrum (NPS), task-based transfer function (TTF), and detectability index (d') were computed for 2-mm-diameter lumen detection. In consensus, two radiologists analyzed the quality of the images from 8 patients who underwent coronary CTA on both CT systems.

RESULTS

For all keV images, fpeak, f50, and d' were higher with SPCCT. The fpeak and f50 were higher with UHR-SPCCT with greater noise and lower d' compared to those of the HR-SPCCT images. Noise magnitude was constant for all energy levels (keV) with both systems, and lower with HR images, and d' decreased as keV decreased. Subjective analysis showed greater lumen sharpness and overall quality for HR and UHR-SPCCT images using all keV, with a greater difference at low keV compared to HR-EID-DECT images.

CONCLUSION

HR and UHR-SPCCT images gave greater detectability of the coronary lumen for 40 to 90 keV VMIs compared to two EID-DECT systems, with benefits of higher lumen sharpness and overall quality.

KEY POINTS

• Compared with 2 dual-energy CT systems, spectral photon-counting CT (SPCCT) improved spatial resolution, noise texture, noise magnitude, and detectability of the coronary lumen. • Use of ultra-high-resolution parameters with SPCCT improved spatial resolution and noise texture and provided high detectability of the coronary lumen, despite an increase in noise magnitude. • In eight patients, radiologists found greater overall image quality with SPCCT for all virtual monochromatic images with a greater difference at low keV, compared with dual-energy CT systems.

First Experience With a Whole-Body Spectral Photon-Counting CT Clinical Prototype

ABSTRACT

Spectral photon-counting computed tomography (SPCCT) technology holds great promise for becoming the next generation of computed tomography (CT) systems. Its technical characteristics have many advantages over conventional CT imaging. For example, SPCCT provides better spatial resolution, greater dose efficiency for ultra-low-dose and low-dose protocols, and tissue contrast superior to that of conventional CT. In addition, SPCCT takes advantage of several known approaches in the field of spectral CT imaging, such as virtual monochromatic imaging and material decomposition imaging. In addition, SPCCT takes advantage of a new approach in this field, known as K-edge imaging, which allows specific and quantitative imaging of a heavy atom-based contrast agent. Hence, the high potential of SPCCT systems supports their ongoing investigation in clinical research settings. In this review, we propose an overview of our clinical research experience of a whole-body SPCCT clinical prototype, to give an insight into the potential benefits for clinical human imaging on image quality, diagnostic confidence, and new approaches in spectral CT imaging.

First In-Human Results of Computed Tomography Angiography for Coronary Stent Assessment With a Spectral Photon Counting Computed Tomography

OBJECTIVES

The aim of this study is to compare the image quality of in vivo coronary stents between an energy integrating detectors dual-layer computed tomography (EID-DLCT) and a clinical prototype of spectral photon counting computed tomography (SPCCT).

MATERIALS AND METHODS

In January to June 2021, consecutive patients with coronary stents were prospectively enrolled to undergo a coronary computed tomography (CT) with an EID-DLCT (IQon, Philips) and an SPCCT (Philips). The study was approved by the local ethical committee and patients signed an informed consent. A retrospectively electrocardiogram-gated acquisition was performed with optimized matching parameters on the 2 scanners (EID-DLCT: collimation, 64 × 0.625 mm; kVp, 120, automatic exposure control with target current at 255 mAs; rotation time, 0.27 seconds; SPCCT: collimation, 64 × 0.275 mm; kVp, 120; mAs, 255; rotation time, 0.33 seconds). The injection protocol was the same on both scanners: 65 to 75 mL of Iomeron (Bracco) at 5 mL/s. Images were reconstructed with slice thickness of 0.67 mm, 512 matrix, XCB (Xres cardiac standard) and XCD (Xres cardiac detailed) kernel, iDose 3 for EID-DLCT and 0.25-mm slice thickness, 1024 matrix, Detailed 2 and Sharp kernel, and iDose 6 for SPCCT. Two experienced observers measured the proximal and distal external and internal diameters of the stents to quantify blooming artifacts. Regions of interest were drawn in the lumen of the stent and of the upstream coronary artery. The difference (Δ S-C) between the respective attenuation values was calculated as a quantification of stent-induced artifacts on intrastent image quality. For subjective image quality, 3 experienced observers graded with a 4-point scale the image quality of different parameters: coronary wall before the stent, stent lumen, stent structure, calcifications surrounding the stent, and beam-hardening artifacts.

RESULTS

Eight patients (age, 68 years [interquartile range, 8]; all men; body mass index, 26.2 kg/m2 [interquartile range, 4.2]) with 16 stents were scanned. Five stents were not evaluable owing to motion artifacts on the SPCCT. Of the remaining, all were drug eluting stents, of which 6 were platinum-chromium, 3 were cobalt-platinum-iridium, and 1 was stainless steel. For 1 stent, no information could be retrieved. Radiation dose was lower with the SPCCT (fixed CT dose index of 25.7 mGy for SPCCT vs median CT dose index of 35.7 [IQ = 13.6] mGy; P = 0.02). For 1 stent, the internal diameter was not assessable on EID-DLCT. External diameters were smaller and internal diameters were larger with SPCCT (all P < 0.05). Consequently, blooming artifacts were reduced on SPCCT (P < 0.05). Whereas Hounsfield unit values within the coronary arteries on the 2 scanners were similar, the Δ S-C was lower for SPCCT-Sharp as compared with EID-DLCT-XCD and SPCCT-Detailed 2 (P < 0.05). The SPCCT received higher subjective scores than EID-DLCT for stent lumen, stent structure, surrounding calcifications and beam-hardening for both Detailed 2 and Sharp (all P ≤ 0.05). The SPCCT-Sharp was judged better for stent structure and beam-hardening assessment as compared with SPCCT-Detailed 2.

CONCLUSION

Spectral photon counting CT demonstrated improved objective and subjective image quality as compared with EID-DLCT for the evaluation of coronary stents even with a reduced radiation dose.

Coronary CT Angiography with Photon-counting CT: First-In-Human Results

Background Spatial resolution, soft-tissue contrast, and dose-efficient capabilities of photon-counting CT (PCCT) potentially allow a better quality and diagnostic confidence of coronary CT angiography (CCTA) in comparison to conventional CT. Purpose To compare the quality of CCTA scans obtained with a clinical prototype PCCT system and an energy-integrating detector (EID) dual-layer CT (DLCT) system. Materials and Methods In this prospective board-approved study with informed consent, participants with coronary artery disease underwent retrospective electrocardiographically gated CCTA with both systems after injection of 65-75 mL of 400 mg/mL iodinated contrast agent at 5 mL/sec. A prior phantom task-based quality assessment of the detectability index of coronary lesions was performed. Ultra-high-resolution parameters were used for PCCT (1024 matrix, 0.25-mm section thickness) and EID DLCT (512 matrix, 0.67-mm section thickness). Three cardiac radiologists independently performed a blinded analysis using a five-point quality score (1 = insufficient, 5 = excellent) for overall image quality, diagnostic confidence, and diagnostic quality of calcifications, stents, and noncalcified plaques. A logistic regression model, adjusted for radiologists, was used to evaluate the proportion of improvement in scores with the best method. Results Fourteen consecutive participants (12 men; mean age, 61 years ± 17) were enrolled. Scores of overall quality and diagnostic confidence were higher with PCCT images with a median of 5 (interquartile range [IQR], 2) and 5 (IQR, 1) versus 4 (IQR, 1) and 4 (IQR, 3) with EID DLCT images, using a mean tube current of 255 mAs ± 0 versus 349 mAs ± 111 for EID DLCT images (P < .01). Proportions of improvement with PCCT images for quality of calcification, stent, and noncalcified plaque were 100%, 92% (95% CI: 71, 98), and 45% (95% CI: 28, 63), respectively. In the phantom study, detectability indexes were 2.3-fold higher for lumen and 2.9-fold higher for noncalcified plaques with PCCT images. Conclusion Coronary CT angiography with a photon-counting CT system demonstrated in humans an improved image quality and diagnostic confidence compared with an energy-integrating dual-layer CT. © RSNA, 2022 Online supplemental material is available for this article. See also the editorial by Sandfort and Bluemke in this issue.

Performance of Spectral Photon-Counting Coronary CT Angiography and Comparison with Energy-Integrating-Detector CT: Objective Assessment with Model Observer

AIMS

To evaluate spectral photon-counting CT's (SPCCT) objective image quality characteristics in vitro, compared with standard-of-care energy-integrating-detector (EID) CT.

METHODS

We scanned a thorax phantom with a coronary artery module at 10 mGy on a prototype SPCCT and a clinical dual-layer EID-CT under various conditions of simulated patient size (small, medium, and large). We used filtered back-projection with a soft-tissue kernel. We assessed noise and contrast-dependent spatial resolution with noise power spectra (NPS) and target transfer functions (TTF), respectively. Detectability indices (d') of simulated non-calcified and lipid-rich atherosclerotic plaques were computed using the non-pre-whitening with eye filter model observer.

RESULTS

SPCCT provided lower noise magnitude (9-38% lower NPS amplitude) and higher noise frequency peaks (sharper noise texture). Furthermore, SPCCT provided consistently higher spatial resolution (30-33% better TTF10). In the detectability analysis, SPCCT outperformed EID-CT in all investigated conditions, providing superior d'. SPCCT reached almost perfect detectability (AUC ≈ 95%) for simulated 0.5-mm-thick non-calcified plaques (for large-sized patients), whereas EID-CT had lower d' (AUC ≈ 75%). For lipid-rich atherosclerotic plaques, SPCCT achieved 85% AUC vs. 77.5% with EID-CT.

CONCLUSIONS

SPCCT outperformed EID-CT in detecting simulated coronary atherosclerosis and might enhance diagnostic accuracy by providing lower noise magnitude, markedly improved spatial resolution, and superior lipid core detectability.

Feasibility of using post-contrast dual-energy CT for pediatric radiation treatment planning and dose calculation

OBJECTIVES

When iodinated contrast is administered during CT simulation, standard practice requires a separate non-contrast CT for dose calculation. The objective of this study is to validate our hypothesis that since iodine affects Hounsfield units (HUs) more than electron density (ED), the information from post-contrast dual-layer CT (DLCT) would be sufficient for accurate dose calculation for both photon and proton therapy.

METHODS AND MATERIALS

10 pediatric patients with abdominal tumors underwent DLCT scans before and after iodinated contrast administration for radiotherapy planning. Dose distributions with these DLCT-based methods were compared to those with conventional calibration-curve methods that map HU images to ED and stopping-power ratio (SPR) images.

RESULTS

For photon plans, conventional and DLCT approaches based on post-contrast scans underestimated the PTV D99 by 0.87 ± 0.70% (p = 0.18) and 0.36 ± 0.31% (p = 0.34), respectively, comparing to their non-contrast optimization plans. Renal iodine concentration was weakly associated with D99 deviation for both conventional (R² = 0.10) and DLCT (R² = 0.02) approaches. For proton plans, the clinical target volume D99 errors were 3.67 ± 2.43% (p = 0.0001) and 0.30 ± 0.25% (p = 0.40) for conventional and DLCT approaches, respectively. The proton beam range changed noticeably with the conventional approach. Renal iodine concentration was highly associated with D99 deviation for the conventional approach (R² = 0.83) but not for DLCT (R² = 0.007).

CONCLUSION

Conventional CT with iodine contrast resulted in a large dosimetric error for proton therapy, compared to true non-contrast plans, but the error was less for photon therapy. These errors can be greatly reduced in the case of the proton plans if DLCT is used, raising the possibility of using only a single post-contrast CT for radiotherapy dose calculation, thus reducing the time and imaging dose required.

ADVANCES IN KNOWLEDGE

This study is the first to compare directly the differences in the calculated dose distributions between pre- and post-contrast CT images generated by single-energy CT and dual-energy CT methods for photon and proton therapy.

Virtual versus true non-contrast dual-energy CT imaging for the diagnosis of aortic intramural hematoma

PURPOSE

To assess whether virtual non-contrast (VNC) images derived from contrast dual-layer dual-energy computed tomography (DL-DECT) images could replace true non-contrast (TNC) images for aortic intramural hematoma (IMH) diagnosis in acute aortic syndrome (AAS) imaging protocols by performing quantitative as well as qualitative phantom and clinical studies.

MATERIALS AND METHODS

Patients with confirmed IMH were included retrospectively in two centers. For in vitro imaging, a custom-made phantom of IMH was placed in a semi-anthropomorphic thorax phantom (QRM GmbH) and imaged on a DL-DECT at 120 kVp under various conditions of patient size, radiation exposure, and reconstruction modes. For in vivo imaging, 21 patients (70 ± 13 years) who underwent AAS imaging protocols at 120 kVp were included. In both studies, contrast-to-noise ratio (CNR) between hematoma and lumen was compared using a paired t test. Diagnostic confidence (1 = non-diagnostic, 4 = exemplary) for VNC and TNC images was rated by two radiologists and compared. Effective radiation doses for each acquisition were calculated.

RESULTS

In both the phantom and clinical studies, we observed that the CNRs were similar between the VNC and TNC images. Moreover, both methods allowed differentiating the hyper-attenuation within the hematoma from the blood. Finally, we obtained equivalent high diagnostic confidence with both VNC and TNC images (VNC = 3.2 ± 0.7, TNC = 3.1 ± 0.7; p = 0.3). Finally, by suppressing TNC acquisition and using VNC, the mean effective dose reduction would be 40%.

CONCLUSION

DL-DECT offers similar performances with VNC and TNC images for IMH diagnosis without compromise in diagnostic image quality.

KEY POINTS

• Dual-layer dual-energy CT enables virtual non-contrast imaging from a contrast-enhanced acquisition. • Virtual non-contrast imaging with dual-layer dual-energy CT reduces the number of acquisitions and radiation exposure in acute aortic syndrome imaging protocol. • Dual-layer dual-energy CT has the potential to become a suitable imaging tool for acute aortic syndrome.

Multicolour imaging with spectral photon-counting CT: a phantom study

Background

To evaluate the feasibility of multicolour quantitative imaging with spectral photon-counting computed tomography (SPCCT) of different mixed contrast agents.

Methods

Phantoms containing eleven tubes with mixtures of varying proportions of two contrast agents (i.e. two selected from gadolinium, iodine or gold nanoparticles) were prepared so that the attenuation of each tube was about 280 HU. Scans were acquired at 120 kVp and 100 mAs using a five-bin preclinical SPCCT prototype, generating conventional, water, iodine, gadolinium and gold images. The correlation between prepared and measured concentrations was assessed using linear regression. The cross-contamination was measured for each material as the root mean square error (RMSE) of its concentration in the other material images, where no signal was expected. The contrast-to-noise ratio (CNR) relative to a phosphate buffered saline tube was calculated for each contrast agent.

Results

The solutions had similar attenuations (279 ± 10 HU, mean ± standard deviation) and could not be differentiated on conventional images. However, a distinction was observed in the material images within the same samples, and the measured and prepared concentrations were strongly correlated (R² ≥ 0.97, 0.81 ≤ slope ≤ 0.95, -0.68 ≤ offset ≤ 0.89 mg/mL). Cross-contamination in the iodine images for the mixture of gold and gadolinium contrast agents (RMSE = 0.34 mg/mL) was observed. CNR for 1 mg/mL of contrast agent was better for the mixture of iodine and gadolinium (CNR_iodine = 3.20, CNR_gadolinium = 2.80) than gold and gadolinium (CNR_gadolinium = 1.67, CNR_gold = 1.37).

Conclusions

SPCCT enables multicolour quantitative imaging. As a result, it should be possible to perform imaging of multiple uptake phases of a given tissue/organ within a single scan by injecting different contrast agents sequentially.

Calibration and error analysis of metal-oxide-semiconductor field-effect transistor dosimeters for computed tomography radiation dosimetry

PURPOSE

Metal-oxide-semiconductor field-effect transistors (MOSFETs) serve as a helpful tool for organ radiation dosimetry and their use has grown in computed tomography (CT). While different approaches have been used for MOSFET calibration, those using the commonly available 100 mm pencil ionization chamber have not incorporated measurements performed throughout its length, and moreover, no previous work has rigorously evaluated the multiple sources of error involved in MOSFET calibration. In this paper, we propose a new MOSFET calibration approach to translate MOSFET voltage measurements into absorbed dose from CT, based on serial measurements performed throughout the length of a 100-mm ionization chamber, and perform an analysis of the errors of MOSFET voltage measurements and four sources of error in calibration.

METHODS

MOSFET calibration was performed at two sites, to determine single calibration factors for tube potentials of 80, 100, and 120 kVp, using a 100-mm-long pencil ion chamber and a cylindrical computed tomography dose index (CTDI) phantom of 32 cm diameter. The dose profile along the 100-mm ion chamber axis was sampled in 5 mm intervals by nine MOSFETs in the nine holes of the CTDI phantom. Variance of the absorbed dose was modeled as a sum of the MOSFET voltage measurement variance and the calibration factor variance, the latter being comprised of three main subcomponents: ionization chamber reading variance, MOSFET-to-MOSFET variation and a contribution related to the fact that the average calibration factor of a few MOSFETs was used as an estimate for the average value of all MOSFETs. MOSFET voltage measurement error was estimated based on sets of repeated measurements. The calibration factor overall voltage measurement error was calculated from the above analysis.

RESULTS

Calibration factors determined were close to those reported in the literature and by the manufacturer (~3 mV/mGy), ranging from 2.87 to 3.13 mV/mGy. The error σ_V of a MOSFET voltage measurement was shown to be proportional to the square root of the voltage V: σV=cV where c = 0.11 mV. A main contributor to the error in the calibration factor was the ionization chamber reading error with 5% error. The usage of a single calibration factor for all MOSFETs introduced an additional error of about 5-7%, depending on the number of MOSFETs that were used to determine the single calibration factor. The expected overall error in a high-dose region (~30 mGy) was estimated to be about 8%, compared to 6% when an individual MOSFET calibration was performed. For a low-dose region (~3 mGy), these values were 13% and 12%.

CONCLUSIONS

A MOSFET calibration method was developed using a 100-mm pencil ion chamber and a CTDI phantom, accompanied by an absorbed dose error analysis reflecting multiple sources of measurement error. When using a single calibration factor, per tube potential, for different MOSFETs, only a small error was introduced into absorbed dose determinations, thus supporting the use of a single calibration factor for experiments involving many MOSFETs, such as those required to accurately estimate radiation effective dose.

Quantifying potential reduction in contrast dose with monoenergetic images synthesized from dual-layer detector spectral CT

OBJECTIVE

To estimate the potential dose reduction in iodinated contrast when interpreting monoenergetic images from spectral CT.

METHODS

51 paediatric patients received contrast-enhanced CT simulation for radiation therapy using a single-source, dual-layer detector spectral CT. The contrast-to-noise ratios (CNRs) of blood vessels were measured relative to surrounding soft tissue. CNRs on monoenergetic 40-70 keV images were compared with polychromatic 120 kVp images. To compare with in vivo results, a phantom with iodine inserts (2-20 mg ml-1 concentration) was scanned and CNRs were calculated relative to water background.

RESULTS

Monoenergetic keV and body site had significant effects on CNR ratio (p < 0.0001). Across all body sites, the mean CNR ratio (monoenergetic/polychromatic CNR) was 3.3 (20th percentile [%20] 2.6), 2.4 (%20 2.1), 1.7 (%20 1.5), 1.2 (%20 1.0) for 40, 50, 60 and 70 keV images, respectively. Image noise was highest at 40 keV and lowest at 70 keV. Phantom measurements indicated that the same CNR as 120 kVp images can be achieved with a 4.0-fold lower iodine concentration on 40 keV images and 2.5-fold lower on 50 keV images.

CONCLUSION

50 keV monoenergetic images provided the best balance of improved CNR on all studies (mean 2.4-fold increase in vivo) for enhancing vessels vs image noise. A 50% reduction in contrast dose on a 50 keV image should maintain comparable or better CNR as compared with polychromatic CT in over 80% of CT studies. Advances in knowledge: Use of a novel, single-source, dual-layer detector spectral CT scanner to improve visualization of contrast-enhanced blood vessels will reduce the amount of iodinated contrast required for radiation oncology treatment planning.

Building on the past--challenging the future: will genomics provide the solution to hypertension?

Hypertension is one of the major common polygenic and multifactorial diseases, and continues to constitute a major cause of morbidity and mortality worldwide. The pathophysiological mechanisms underlying hypertension have not been elucidated, which significantly limits our ability to treat and prevent hypertension. A frequently asked question is whether genomics will provide the solution to the many remaining unanswered questions as to the causes of hypertension. Genomics, an art by its own virtue, holds its promises, yet the questions we are asking of genomics must be well defined for genomics to meet at least some of our expectations. The hopes and promises of genomics are high and one of the major hopes is that genomics will improve our understanding of the pathophysiology of hypertension and enable us to classify hypertensive syndromes more succinctly and enhance our ability to provide patients with specific anti-hypertensive therapy as well as predict outcome. There is still much to be done but perseverance in the task and a firm belief in genomics and in the immense potential of the human genome is essential.

A jeep trip with young adult cancer survivors: lessons to be learned

The paper describes major areas of concern and preferred coping mechanisms among 17 young survivors of childhood cancer who participated in an 8-day adventure jeep trip in Greece. The paper also deals with various aspects of "adventure therapeutic activity." The participants were videotaped and interviewed during and after the trip. The data gathered were studied through a process of content analysis. Survivors' main areas of concern included: coping with uncertainty, dependency versus autonomy, social exclusion, separation processes, body image, intimacy, sexuality and fertility, and occupation. Preferred coping styles included use of humor, religious beliefs, cognitive reframing, and use of imagination. The trip provided the young adults with an opportunity for physical challenges, and they reported improvements in self-confidence, independence, and social contacts. The trip served as a catalyst for further group activities and group support. An adventure trip seems to be a suitable therapeutic milieu for young adult cancer survivors, where they can profit from a nurturing setting in which rehabilitation-promoting resources are available. It still remains to be seen which components of such an activity are more health promoting, what contraindications there could be, if any, for participation in such a trip, and what role health professionals should play in this kind of activity.

The newly inbred cohen diabetic rat: a nonobese normolipidemic genetic model of diet-induced type 2 diabetes expressing sex differences

The newly inbred Cohen diabetic rat is an exceptional experimental model of diet-induced type 2 diabetes mellitus that is the result of secondary inbreeding nearly 30 years after it originally had been established. Animals from the original colony were selectively inbred by stringent criteria for 10 additional generations, bringing overall inbreeding to >50 generations. The metabolic phenotypes of the resulting contrasting strains, designated as the Cohen diabetic-sensitive (CDs) and -resistant (CDr) rats, were characterized. The phenotype of the CDs strain that was fed a regular diet consisted of fasting normoglycemia, normal glucose tolerance to intraperitoneal glucose loading, normal fasting insulin levels, and a normal insulin response to glucose loading. In contrast, CDs rats that were fed a custom-prepared high-sucrose low-copper diabetogenic diet became overtly diabetic: fasting glucose levels were normal or elevated, and the blood glucose insulin response to glucose loading was markedly abnormal. CDr rats that were fed a regular or diabetogenic diet did not develop diabetes and maintained normal glucose tolerance and insulin secretion. A striking sex difference was observed in CDs rats that were fed a diabetogenic diet: males had a lower growth rate and a more severe glucose intolerance pattern than females. Gonadectomy shortly after weaning did not prevent the development of the diabetic phenotype in its early phase in either sex but markedly attenuated its expression in males at a later phase, abolishing the sex differences. Alternate-day feeding, as opposed to daily feeding, also attenuated the metabolic phenotype in males. The development of the diabetic phenotype in CDs rats that were fed a diabetogenic diet was not accompanied by obesity or hyperlipidemia. The genetic profile of the strains was established using 550 microsatellite markers evenly distributed throughout the rat genome. The rate of homozygosity within strain was > or = 96%. The rate of polymorphism between the contrasting strains was 43%. We conclude that the metabolic phenotypes of the rebred colony of CDs and CDr rats and their genetic makeup render the Cohen diabetic rat a useful experimental model that is highly suitable for studying the interaction between nutritional-metabolic environmental factors and genetic susceptibility (sensitivity and resistance) for the development of type 2 diabetes. The model is also distinctively useful for investigating the effect of sex on the expression of the diabetic phenotype.

Genetic models of hypertension in experimental animals

Genetic animal models are central to ongoing efforts to elucidate the pathophysiology and genetic basis of hypertension. The rat is the leading species in experimental hypertension. Several rat models of hypertension are available for research, including inbred strains, congenic lines, transgenic animals and recombinant inbred strains. Each of these models has been designed to express different phenotypes, including spontaneous hypertension, salt sensitivity, stress sensitivity and susceptibility to end-organ damage. All these models have been extremely useful in the search for the physiological mechanisms that underlie hypertension, but some of them have been specifically designed for detecting the hypertension genes. This latter task is extremely complex in spontaneous hypertension, but genetic animal models may simplify the task by enabling to focus on specific phenotypes. Despite intensive efforts over nearly 3 decades, the genetic basis of hypertension has not been unveiled so far in the rat or in other species. Recent dense mapping of the rat genome, the development of new strategies and technologies in molecular genetics including differential gene expression, expressed sequence tags and DNA biochips render hope that the formidable task of identification of new candidate genes in hypertension will move another major step forward. Once these genes are identified, their function and role in hypertension will have to be determined, utilizing functional genomic strategies and bioinformatics. Finally, the findings in genetic animal models of hypertension will have to be extrapolated to humans by homology and syntenic mapping strategies.

The lack of a modulating effect of non-genetic factors (age, gonads and maternal environment) on the phenotypic expression of the salt-susceptibility genes in the Sabra rat model of hypertension

OBJECTIVE

This study was designed to test the hypothesis that non-genetic factors such as age, gonads and maternal environment modulate the expression of the salt-susceptibility genes and affect the blood pressure response to salt-loading (salt-sensitivity and salt-resistance) in the Sabra rat model of hypertension.

METHODS

The blood pressure response to salt-loading was studied in Sabra hypertension prone (SBH/y) and Sabra hypertension resistant (SBN/y) rats of both sexes: (1) at 1, 3, 6, 9 and 12 months of age, (2) in adult rats after orchiectomy or oophorectomy, and (3) in animals that had been raised and nourished from birth to weaning by a foster mother from the contrasting strain. In each of the study protocols, systolic blood pressure was measured at baseline by the tail cuff method, animals were salt-loaded with deoxycorticosterone acetate, and blood pressure was measured again after 4 weeks.

RESULTS

Basal blood pressure at all the ages studied and in both sexes was on average 10-15 mmHg higher in SBH/y than in SBN/y. Salt-loading in SBN/y of both sexes aged 1-12 months did not induce any significant increment in blood pressure. Salt-loading in SBH/y, in contrast, caused a highly significant rise in systolic blood pressure, of 40 mmHg or more at all the ages studied. There was no age difference or sex dependence in the magnitude of the blood pressure response to salt Oophorectomy or orchiectomy did not affect the levels of basal blood pressure nor prevent the hypertensive response to salt-loading in SBH/y or the lack of a hypertensive response in SBN/y rats. Gonadectomy did not affect blood pressure in salt-loaded hypertensive SBH/y nor in salt-loaded normotensive SBN/y. The basal blood pressure and the blood pressure responses of SBH/y and SBN/y of both sexes raised by foster mothers of the contrasting strains from birth to weaning were not different from those observed when raised by their natural mothers.

CONCLUSIONS

This study indicates that salt-sensitivity in SBH/y and salt-resistance in SBN/y are not age-dependent phenomena; that the magnitude of the BP response to salt-loading is not sex-dependent; and that neither gonadectomy nor the maternal environment affect the blood pressure response to salt-loading in the adult animal of either strain. These non-genetic factors thus do not modulate expression of the salt-susceptibility genes in the Sabra genetic model of salt-sensitive hypertension.

Regulation by sodium intake of type 1 angiotensin II receptor mRNAs in the kidney of Sabra rats

OBJECTIVE

To study the relationship between the sensitivity to sodium content of the diet in terms of development of hypertension and the regulation of the expression of type 1 angiotensin II receptor subtypes by such a diet.

METHODS

The expression of angiotensin II receptor subtype (AT1A and AT1B) mRNAs was studied by quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) in the four zones of the kidneys of Sabra rats, sensitive or resistant to DOCA salt-induced hypertension (SBH/y and SBN/y, respectively). Rats were fed a high (8%) or normal (0.4%) NaCl diet. As vasopressin is known to be elevated in SBH/y rats and to be involved in DOCA-salt hypertension, we studied an additional group of SBH/y rats, fed a high sodium diet, enriched in water.

RESULTS

With the absence of DOCA, SBH/y rats did not develop hypertension. The high sodium diet induced a greater fall in the plasma renin activity in the SBH/y (-95%) than in the SBN/y (-63%). In the cortex (C) and inner stripe (IS), the high sodium diet decreased AT1A and AT1B mRNAs in SBH/y and SBN/y, with a higher magnitude for SBH/y, than for SBN/y (C, -28 versus -20%; IS, -42 versus -20%). The addition of water to the high sodium diet lessened the effect of sodium in the C and IS, although the plasma renin activity (PRA) was not altered.

CONCLUSION

A high sodium diet significantly decreases both AT1A and AT1B gene expression in two specific zones of the rat kidney containing the target cells of angiotensin II (C and IS). This down-regulation is organ-specific since it was observed in the kidney and adrenals, but not in the liver. Finally, SBH/y and SBN/y rats differ in the basal level of AT1 mRNA expression in the IS, and in the ability to modulate AT1 mRNA level under sodium intake.

[Angiotensin converting enzyme (ACE) gene polymorphism in a diabetic cohort and diabetic nephropathy]

The renin-angiotensin system is thought to play an important role in the pathophysiology of kidney disease in diabetes. Previous studies have shown a possible association between the D allele of the angiotensin converting enzyme (ACE) gene, known to be associated with higher circulating levels of ACE, and increased risk of developing nephropathy in NIDDM. The present study investigated the distribution of ACE gene genotypes in the general population and patients with NIDDM, the association between the D allele and diabetic nephropathy, and the association between the ACE genotype and involvement of other target organs in NIDDM. The ACE genotype (insertion/deletion I/D) was determined in all subjects, subsequently divided into 3 groups based on their polymorphism (DD, DI and II). The presence of nephropathy was defined by an albumin-creatinine ratio of 30 mg/g or greater (mean of 2 first morning urine samples). In the general population most had the D allele (DD or ID) and a minority the II genotype. There was no association between genotype and hypertension, ischemic heart disease, hyperlipidemia, and cerebrovascular or peripheral vascular disease. In diabetics the genotype distribution was not different from that in the general population. Within the diabetic group, there was no association between genotype and hypertension, hyperlipidemia, duration of diabetes, or HbA1C levels. Nephropathy, found in 81 of the 156 with NIDDM, was not associated with genotype. Diabetic nephropathy was not associated with retinopathy, neuropathy, or ischemic heart, cerebrovascular or peripheral vascular disease. We conclude that in the population sampled, there was no association between the D allele of the ACE gene and the risk of developing nephropathy in NIDDM.

Farnesol blocks the L-type Ca2+ channel by targeting the alpha 1C subunit

We recently demonstrated that farnesol, a 15-carbon isoprenoid, blocks L-type Ca2+ channels in vascular smooth muscle cells. To elucidate farnesol's mechanism of action, we performed whole-cell and perforated-patch clamp experiments in rat aortic A7r5 cells and in Chinese hamster ovary (CHO) C9 cells expressing smooth muscle Ca2+ channel alpha 1C subunits. Farnesol dose-dependently and voltage-independently inhibited Ba2+ currents in both A7r5 and CHOC9 cells, with similar half-maximal inhibitions at 2.6 and 4.3 micromol/L, [corrected] respectively (P=NS). In both cell lines, current inhibition by farnesol was prominent over the whole voltage range without changes in the current-voltage relationship peaks. Neither intracellular infusion of the stable GDP analogue guanosine-5'-O-(2-thiodiphosphate) (100 micromol/L) [corrected] via the patch pipette nor strong conditioning membrane depolarization prevented the inhibitory effect of farnesol, which indicates G protein-independent inhibition of Ca2+ channels. In an analysis of the steady-state inactivation curve for voltage dependence, farnesol induced a significant, negative shift ( approximately 10 mV) of the potential causing 50% channel inactivation in both cell lines (P<0. 001). In contrast, the steepness factor characterizing the voltage sensitivity of the channels was unaffected. Unlike pharmacological Ca2+ channel blockers, farnesol blocked Ca2+ currents in the resting state: initial block was 63+/-8% in A7r5 cells and 50+/-9% in CHOC9 cells at a holding potential of -80 mV. We then gave 500 mg/kg body weight farnesol by gavage to Sabra hypertensive and normotensive rats and found that farnesol reduced blood pressure significantly in the hypertensive strain for at least 48 hours. We conclude that farnesol may represent an endogenous smooth muscle L-type Ca2+ channel antagonist. Because farnesol is active in cells expressing only the pore-forming alpha1 subunit, the data further suggest that this subunit represents the molecular target for farnesol binding and principal action. Finally, farnesol has a blood pressure-lowering action that may be relevant in vivo.

Role of chromosome X in the Sabra rat model of salt-sensitive hypertension

We carried out a total genome screen in the Sabra rat model of hypertension to detect salt-susceptibility genes. We previously reported in male animals the presence of 2 major quantitative trait loci (QTLs) on chromosome 1 that together accounted for most of the difference in the blood pressure (BP) response to salt loading between Sabra hypertension-prone rats (SBH/y) and Sabra hypertension-resistant rats (SBN/y). In females, we reported on 2 major QTLs on chromosomes 1 and 17 that together accounted for only two thirds of the difference in the BP response between the strains. On the basis of phenotypic patterns of inheritance in reciprocal F2 crosses, we proposed a role of the X chromosome. We therefore continued the search for the missing QTL in females that would account for the remaining difference in the BP response between the 2 strains using newly developed microsatellite markers and focusing on chromosome X. We screened an F2 cross, consisting of 371 females and 336 males, using 19 polymorphic chromosome X microsatellite markers. We analyzed the averages of BP by genotype using ANOVA and the individual data using MAPMAKER/QTL. In female F2 progeny, we identified a segment on chromosome X that spans over 33.4 cM and shows significant cosegregation (P<0.001) of 14 microsatellite markers (demarcated by DXRat4 and DXMgh10) with systolic BP after salt loading. This segment has 2 apparent peaks at DXRat4 and DXRat13, with a BP effect of 14 mm Hg for each. Multipoint linkage analysis with a free model detected 3 peaks (logarithm of the odds ratio [LOD] score >4.3) within the same chromosomal segment: One between DXMgh9 and DXMit4 (LOD 4.9; 6.1% of variance), a second between DXMgh12 and DXRat8 (LOD 5.2; 7.2% of variance), and a third between DXRat2 and DXRat4 (LOD 5.8; 7.5% of variance). On the basis of these findings and until congenic strains become available, our working assumption is that within chromosome X, 1 to 3 genetic loci contribute importantly to the BP response of female Sabra rats to salt. In male F2 progeny, we detected no significant cosegregation of any region on chromosome X with the BP response to salt loading. We conclude that in the female rat, salt susceptibility is mediated by 3 to 5 gene loci on chromosomes 1, 17, and X, whereas in the male rat, the X chromosome does not affect the BP response to salt.

Does the Sabra hypertension-prone rat represent a model of salt or mineralocorticoid sensitivity?

OBJECTIVES

Since the Sabra experimental model of hypertension was developed, it has been known as a model of salt-susceptible hypertension. Because the hypertensive response of the Sabra hypertension-prone strain (SBH/y) is classically elicited by salt loading with a combination of deoxycorticosterone acetate (DOCA) and salt, doubt has now been cast on whether the hypertensive response is due to sensitivity to salt or to mineralocorticoids. The present study was designed to resolve this question.

MATERIALS AND METHODS

We studied the blood pressure response of SBH/y to various modes of salt loading. Animals were salt-loaded by administration of: 1% NaCl in drinking water and subcutaneous implantation of a 25 mg DOCA pellet (DOCA-salt); DOCA alone; 1% NaCl in drinking water alone; or 8% NaCl in chow alone. Blood pressure was determined by the tail-cuff method in awake and undisturbed animals.

RESULTS

Within 4 weeks, the DOCA-salt treatment elicited the full hypertensive response previously reported in the SBH/y strain. Salt loading with 8% NaCl in chow reproduced the full hypertensive response observed with DOCA-salt, except that it occurred only after 7 weeks of treatment. Salt loading with DOCA alone raised blood pressure moderately and to a maximal level within 3 weeks; the magnitude of the blood pressure response was, however, significantly smaller than that observed with DOCA-salt or 8% NaCl in chow. Administration of 1% NaCl in water alone elicited no hypertensive response.

CONCLUSIONS

The hypertensive response to salt loading in the Sabra experimental model of hypertension is an expression primarily of salt sensitivity, as it can be fully reproduced with salt alone, but not with DOCA alone. The use of the DOCA-salt mode of salt loading in this model, as opposed to salt loading with 8% salt in chow, is a useful way of accelerating the development of salt-sensitive hypertension in SBH/y, which shortens, and therefore facilitates, phenotyping.

Genetic basis of salt-susceptibility in the Sabra rat model of hypertension

The Sabra salt-sensitive SBH/y and salt-resistant SBN/y rats constitute a unique experimental model of hypertension in which salt-susceptibility is genetically determined and expressed only after salt-loading, without the development of spontaneous hypertension. To determine the genetic basis of salt-susceptibility in the Sabra rats, the candidate gene and total genome screen approaches were adopted. The likely candidate genes in this model incorporate salt-related physiological mechanisms such as the nitric oxide system, the arginine vasopressin axis and the epithelial sodium channel. In the random genome search scheme for culprit genes, SBH/y and SBN/y were cross-bred. A highly unusual and composite mode of transmission of salt-susceptibility was found in this cross, emphasizing the complexity of the genetic basis of salt-susceptibility. Linkage analysis of the entire rat genome with a large number of widely distributed microsatellite markers identified three putative gene loci on chromosomes 1 and 17 that contribute importantly to salt-sensitivity and/or resistance, and uncovered sex specificity in the role that salt-susceptibility genes fulfill in the development of hypertension.

Salt susceptibility maps to chromosomes 1 and 17 with sex specificity in the Sabra rat model of hypertension

Random genome screening was initiated in the Sabra rat model of hypertension in search of genes that account for salt sensitivity or salt resistance in terms of the development of hypertension. Female salt-sensitive Sabra hypertension-prone (SBH/y) rats were crossed with male salt-resistant Sabra hypertension-resistant (SBN/y) rats, resulting in an F2 cohort consisting of 100 males and 132 females. Systolic blood pressure (BP) was measured in rats at 6 weeks of age under basal conditions and after 4 weeks of salt loading. Genotypes for 24 polymorphic microsatellite markers localized to chromosome 1 and for 8 markers localized to chromosome 17 were determined in F2 and cosegregation with BP was evaluated by ANOVA and multipoint linkage analysis. Basal BP did not cosegregate with any locus on chromosomes 1 or 17. In contrast, BP after salt loading showed significant cosegregation with three QTLs, two on chromosome 1 and one on chromosome 17, designated SS1a, SS1b, and SS17, respectively; the maximal logarithm of the odds (LOD) scores were 4.71, 4.91, and 3.43, respectively. Further analysis revealed sexual dimorphism. In male F2, BP response to salt loading cosegregated with one QTL (LOD score 4.52) and a second QTL (LOD score 2.98), both on chromosome 1 and coinciding with SS1a and SS1b, respectively. In female rats, BP response cosegregated with one QTL on chromosome 1 (LOD score 3.08) coinciding with SS1b, and with a second QTL on chromosome 17 (LOD score 3.66) coinciding with SS17. In males, the additive effects of the two QTLs on chromosome 1 accounted for most of the BP variance to salt loading, whereas in females the additive effects of the QTLs on chromosomes 1 and 17 accounted for over two thirds of the variance. These results identify three putative gene loci on chromosomes 1 and 17 that contribute importantly to salt sensitivity and/or resistance and uncover sex specificity in the role that salt susceptibility genes fulfill in the development of hypertension.

Glomerular basement membrane polyanionic sites and nitric oxide in genetically salt-sensitive and resistant hypertensive rats

Cationic colloid gold, a polycationic histochemical probe, was used to analyze the distribution of glomerular basement membrane (GBM) polyanions, including heparan sulfate protoglycan in genetic salt-sensitive (SBH/Y) and resistant (SBN/Y) hypertensive rats, with or without high dietary salt intake. GBM morphology, renal function and nitric oxide, as measured by plasma and urine nitrite (NO2) and nitrate (NO3) were also determined. In the salt-sensitive rats the high-salt dietary intake resulted in severe hypertension, proteinuria and decreased glomerular filtration rate. After 1 month of high-salt intake, the average width of the GBM of salt-sensitive rats was higher by 27% than that of salt-resistant rats. The number of GBM anionic sites (lamina rata externa and interna) was much lower in both salt-sensitive and salt-resistant groups after 1 month of salt loading, 8.04+/-0.36 and 7.8+/-0.25 counts/cm, respectively, compared to the respective values of non-salt-loaded animals, 20.58+/-1.08 counts/cm in the SBH/Y (p < 0.001) and 21+/-1.86 counts/cm in the SBN/Y (p < 0.001). A decreased nitric oxide production was found in the salt-sensitive rats before and after salt loading compared with the salt-resistant group. No correlation was found between the nitric oxide changes and the GBM modifications. It is concluded that high-salt intake may be deleterious to the permselectivity of the GBM. It is suggested that salt restriction in hypertension may have a beneficial effect in preventing GBM permselectivity changes and proteinuria.

Nitric oxide synthase and renin-angiotensin system gene expression in salt-sensitive and salt-resistant Sabra rats

The molecular mechanisms of salt sensitivity and the contribution of the kidney to salt-induced hypertension in Sabra rats are imperfectly defined. We investigated the expression of the nitric oxide (NO) system (endothelial, inducible, and neural NO synthases) and renin-angiotensin system (renin, angiotensinogen, and angiotensin II type 1A receptor) gene components in the kidneys of SBN/y (salt-resistant) and SBH/y (salt-sensitive) Sabra rat substrains, with and without deoxycorticosterone acetate (DOCA)-salt treatment. We also looked for immunocytochemical evidence of angiotensin II, the effector peptide of the renin-angiotensin system. Inducible and neural NO synthase gene expression values were lower in SBH/y than in SBN/y before and after DOCA-salt treatment. The gene expression level of endothelial NO synthase was not different in SBH/y and SBN/y, either with or without DOCA salt. Renin gene expression was significantly higher in kidneys of SBN/y than in kidneys of SBH/y rats, whereas angiotensinogen gene expression was significantly lower in SBN/y. After DOCA-salt treatment, renin gene expression was strongly suppressed in both strains but more so in SBH/y. Angiotensinogen gene expression, on the other hand, was increased by DOCA salt in SBN/y rats so that the two strains were no longer different. Angiotensin II immunoreactivity was significantly higher in SBN/y than in SBH/y; however, after DOCA salt, immunoreactivity in both strains was no longer detectable. Angiotensin II type 1A receptor gene expression was not different between the two strains, either before or after DOCA-salt administration. We conclude that DOCA salt induced a decrease in the activity of the renin-angiotensin system but did not change NO synthase gene expression in SBH/y and SBN/y. Inducible and neural NO synthase gene expression values were less in SBH/y than in SBN/y, independent of DOCA-salt administration. Thus, the NO system could explain, at least in part, the salt resistance of SBN/y.

Pressure natriuresis in salt-sensitive and salt-resistant Sabra rats

Salt-resistant (SBN/y) and salt-sensitive (SBH/y) Sabra rats are a useful model of salt-sensitive hypertension with incompletely explored renal mechanisms. We investigated their pressure-natriuresis curves, with and without deoxycorticosterone acetate (DOCA)-salt treatment. To differentiate between extrinsic neural and hormonal mechanisms and intrinsic renal influences, we performed experiments with neural denervation, adrenalectomy, and infusions of vasopressin, norepinephrine, 17-hydroxycorticosterone, and aldosterone as well as without these maneuvers. In untreated SBN/y without controlled neural and circulating hormonal factors, urine flow and sodium excretion increased from 32 to 95 microL/min per gram kidney weight (gkwt) and from 4 to 17 mumol/min per gkwt, respectively, as renal perfusion pressure was increased from 85 to 146 mm Hg. Renal blood flow and glomerular filtration rate were autoregulated and averaged 7.5 and 1.2 mL/min per gkwt. In untreated SBN/y with controlled neural and circulating factors, pressure-diuresis and -natriuresis curves were shifted toward the right, and renal blood flow and glomerular filtration rate ranged between 4.2 and 9.1 or 1 and 1.3 mL/min per gkwt as perfusion pressure was increased from 99 to 164 mm Hg. In both protocols, values in SBH/y did not differ. DOCA-salt increased blood pressure in SBH/y. In SBH/y without controlled neural and hormonal factors, pressure-diuresis and -natriuresis curves were shifted approximately 20 mm Hg toward the right. Fractional sodium and water excretion curves, renal blood flow, and glomerular filtration rate were shifted rightward in parallel. On the other hand, SBH/y with DOCA-salt and controlled neural and hormonal factors had lower sodium and water excretion rates only at the renal perfusion pressure of 150 mm Hg as well as decreased renal blood flow and glomerular filtration rate compared with DOCA-salt SBN/y. These data suggest that both extrinsic and intrinsic factors are responsible for reduced sodium and water excretory capacity in DOCA-salt SBH/y; however, the extrinsic factors may be more important.

Polymorphisms in the carboxy-terminus of the epithelial sodium channel in rat models for hypertension

OBJECTIVE

To investigate whether mutations in the C-terminus of the three subunits of the rat epithelial sodium channel (alphabetagamma-rENaC) contribute to the hypertensive phenotype in five rat models for essential hypertension.

DESIGN

We sequenced the C-terminal regions of alpha-, beta- and gamma-rENaC genes in five different hypertensive rat strains [spontaneously hypertensive rats (SHR), Dahl salt-sensitive (SS/Jr) rats, Milan hypertensive (MHS) rats, Sabra hypertensive (SBH) rats and Lyon hypertensive rats (LHR)] and their normotensive controls [Wistar-Kyoto (WKY) rats, Dahl salt-resistant (SR/Jr) rats, Milan normotensive (MNS) rats, Sabra normotensive (SBN) rats and Lyon normotensive rats (LNR)]. Identified polymorphisms were tested for cosegregation with blood pressure as well as for increased epithelial sodium channel (ENaC) activity.

METHODS

Genomic DNA extracted from hypertensive and normotensive rat strains was amplified by the polymerase chain reaction and polymerase chain reaction fragments were sequenced. Cosegregation analysis was performed to test for correlations between blood pressure and different genotypes. The effects of a polymorphism on ENaC activity were assessed by functional expression in Xenopus laevis oocytes. The chromosomal location of the gene for gamma-ENaC was determined by linkage analysis in an F2 (MHS x MNS) population.

RESULTS

We found no polymorphisms at the C-terminus of alpha- and beta-rENaC in the five rat models tested. We identified two polymorphisms at the C-terminus of the gamma-subunit, one leading to an amino acid change. Milan strains (MNS and MHS) were polymorphic for this mutation. By cosegregation analysis we could exclude the possibility that there was a correlation between blood pressure and this polymorphism. Functional expression of the polymorphism caused no increase in ENaC activity assessed by measurement of the amiloride-sensitive sodium current in Xenopus oocytes. The gene for the gamma-ENAC was located on rat chromosome 1.

CONCLUSIONS

No polymorphisms at the C-terminus of the three subunits of the epithelial sodium channel cosegregating with blood pressure were detected in five different genetic rat models for hypertension. If an altered ENaC activity contributes to the pathogenesis of hypertension in these rats, it must thus arise from mutations in other parts of the protein, from mutations outside the coding region impairing the proper regulation of one of the subunits or from mutations in an ENaC-associated protein.

Proposed therapeutic algorithm for the treatment of anemia of chronic renal failure in pre-dialysis patients with low dose once weekly subcutaneous r-HuEPO. Multicenter Study Group, Israel

Anemia of chronic renal failure (CRF) prior to initiation of dialysis is an important cause of morbidity and requires early therapeutic intervention. The current study was designed to investigate the efficacy and tolerability of a therapeutic algorithm for anemia of CRF in pre-dialysis patients which is based on low dose once-a-week subcutaneous (s.c.) administration of recombinant human erythropoietin (r-HuEPO). Thirty-one patients participated in a prospective open-label multicenter study. At baseline, hemoglobin was 8.8+/-0.1 g/dl, transferrin saturation 27+/-2%, ferritin 207+/-28 ng/ml and serum creatinine 4.7+/-0.2 mg/dl. Treatment with r-HuEPO was started at a fixed s.c. dose of 4,000 units once weekly, irrespective of body weight, and titrated upwards or downwards according to a predetermined algorithm. Hemoglobin rose to levels >10 g/dl within 8 weeks and remained stable throughout the remaining period of the study. By week 24, most patients required <or =4,000 units/week as maintenance dose. Transferrin saturation and ferritin concentration tended to fall during the course of r-HuEPO treatment, despite iron supplementation. There was no change in white blood cell or platelet count. Eight patients required an increase in antihypertensive therapy, but blood pressure remained well-controlled. Twelve patients failed to complete the full length of the study, 7 of them because dialysis had to be initiated. The rate of decline in kidney function, however, was not altered by r-HuEPO. We conclude that the proposed therapeutic algorithm is practical, efficacious, safe, and cost-effective.

Development, genotype and phenotype of a new colony of the Sabra hypertension prone (SBH/y) and resistant (SBN/y) rat model of slat sensitivity and resistance

OBJECTIVES

Variations in the blood pressure response to salt-loading, the lack of quality control measures, and the need to prepare the strains for genetic studies led to renewed secondary inbreeding of the original colony of Sabra hypertension prone (SBH) and resistant (SBN) rats in order to regain genotypic and phenotypic homogeneity of the substrains.

METHODS

Animals from the original breeding colony were selectively inbred for basal normotension and for susceptibility or resistance to the development of hypertension following salt-loading with deoxycorticosterone acetate (DOCA)-salt. Efficacy of inbreeding was tested by genome screening with 416 microsatellite primer sets. Phenotyping was based on measurements of systolic blood pressure by the tail-cuff methodology in awake, undisturbed animals maintained on standard diet and after salt-loading with DOCA-salt. Telemetric measurements of blood pressure were performed in a small number of animals to validate tail-cuff measurements.

RESULTS

Animals from the new colony were designated SBH/y and SBN/y to differentiate from the original colony. Fourteen generations have been inbred over the past 4 years. Of the 402 microsatellites that amplified, 183 (45.5%) were polymorphic between the two substrains, and not a single locus was found to be heterozygous in either substrain. Phenotypic characteristics are provided for SBH/ y and SBN/y rats with respect to tail-cuff systolic blood pressure. The values obtained, which were validated by telemetry, demonstrate classical features of salt sensitivity or resistance, respectively.

CONCLUSIONS

The genetic homogeneity found in SBH/y and SBN/y, the phenotype demonstrating salt-sensitivity or salt-resistance in terms of development of hypertension, and the relatively high frequency of informative genetic markers identify this Sabra rat model as highly suited for studies concerning the molecular genetics of gene-environment interactions affecting blood pressure regulation.

Disparate expression of the AVP gene in Sabra hypertension-prone and hypertension-resistant rats

We recently re-inbred the original colony of SBH-SBN rats, a model of salt-induced hypertension. In the course of phenotyping the new colony, SBH/y were found to excrete a lower urine flow with a higher urine osmolality than SBN/y. Thus disparate water handling between the substrains, a phenotype characteristic of the original colony, was retained throughout the selection procedure and transmitted down the generations to the new colony. As water handling is directly linked to arginine vasopressin (AVP) and in view of potential linkage of this phenotype to salt sensitivity or resistance in terms of the development of hypertension, the AVP axis was further investigated in the new substrains. Basal plasma AVP levels were higher in SBH/y (2.86 +/- 0.22 pg/ml; n = 10) than in SBN/y (1.98 +/- 0.11 pg/ml; n = 10, P < 0.05). Water deprivation for 48 h increased plasma AVP levels severalfold in both substrains to similar levels. Niravoline, a kappa receptor agonist that inhibits central release of AVP, produced at 0.6 and 0.9 mg/kg a more profound diuretic effect in SBN/y than in SBH/y, suggesting greater pituitary release of AVP into the circulation of SBH/y. AVP mRNA contents were compared in SBH/y and SBN/y rats in whole hypothalamic extracts and in the supraoptic (SON) and paraventricular (PVN) nuclei by RNA protection assay. Under basal conditions, AVP mRNA content (in ng) in the hypothalamus of SBH/y was 4.48 +/- 0.52 (n = 29) and of SBN/y was 3.13 +/- 0.35 (n = 30), P < 0.05; in the SON of SBH/y, AVP mRNA content was 3.62 +/- 0.44 (n = 11) and of SBN/y was 2.21 +/- 0.54 (n = 10), P < 0.05; in the PVN of SBH/y, AVP mRNA content was 0.78 +/- 0.16 (n = 9) and of SBN/y was 0.77 +/- 0.13 (n = 11, not significant). Thus the differences in hypothalamic AVP mRNA were primarily in the SON. Water deprivation as well as salt loading (8% NaCl) induced a significant elevation in AVP mRNA content in SBN/y but a blunted response in SBH/y. These data suggest that there is genetically transmitted enhanced hypothalamic expression of the AVP gene in SBH/y compared with SBN/y which results, under basal conditions, in greater pituitary release of AVP, in higher plasma AVP levels, and in increased renal concentrating activity. As AVP has been implicated in various forms of hypertension, these findings render AVP a candidate gene for salt sensitivity or resistance in the Sabra rat model of hypertension.

Aldosterone induction and epithelial distribution of CHIF

CHIF is a recently cloned, corticosteroid-induced gene which evokes K+ channel activity in oocytes (B. Attali, H. Latter, N. Rachamim, and H. Garty. Proc. Natl. Acad. Sci. USA 92: 6092-6096, 1995). To further characterize the possible role of this gene in epithelial ion transport, we have studied its epithelial distribution and hormonal induction. Northern hybridizations indicate that the zonal distribution of CHIF mRNA in kidney is: papilla >>medulla>> cortex. High levels of CHIF were also detected in a primary culture from inner medullary collecting duct (IMCD). Perfusing rats with < 20 nM aldosterone through osmotic minipumps evoked a 22.4 +/- 1.9-fold increase in colonic CHIF. A significant increase was observed 3 h after administrating the corticosteroid, but maximal response was detected only after a 72-h incubation. This response appears to be mineralocorticoid specific; perfusing or injecting rats with maximal doses of dexamethasone did not evoke a further increase in CHIF mRNA. In contrast, high levels of CHIF are expressed in kidney papilla and IMCD primary culture, irrespective of corticosteroid treatment. Thus, like the apical Na+ channel and the H(+)-K(+)-adenosinetriphosphatase, CHIF is mineralocorticoid induced in the colon but constitutively expressed in kidney.

The use of standard imaging techniques and their diagnostic value in the workup of renal colic in the setting of intractable flank pain

OBJECTIVES

This study reviews the rate at which diagnostic imaging techniques are used in patients with intractable flank pain attributed to renal colic who are admitted to the hospital through the emergency room and determines the diagnostic values of plain film of the abdomen {kidney, ureter, bladder [KUB]} and of ultrasonography (US) of the urinary tract, using intravenous urography (IVU) as the gold standard for establishing the presence of a calculus.

METHODS

We reviewed the medical records of 288 patients who were admitted to our medical center over a period of 5 consecutive years for intractable flank pain, the admission and working diagnosis in all cases being that of renal colic, and we retrieved all data pertaining to their diagnostic evaluation.

RESULTS

A total of 265 patients (92%) were subjected to KUB, 158 (55%) to IVU, and 135 (45%) to US of the renal-urinary tract. Two diagnostic imaging techniques were used in the same patient in the following combinations: KUB and IVU in 146 patients (51%), KUB and US in 110 (38%), and IVU and US in 60 (21%). Three imaging techniques (IVU, KUB, and US) were utilized in 54 patients (19%). The sensitivity and specificity of KUB alone were 95% and 65%, respectively, and the positive and negative predictive values were 82% and 88%. The sensitivity of US alone was 93%, its specificity 83%, the positive predictive value 93%, and the negative predictive value 83%. The sensitivity of combined KUB and US (requiring both tests to be positive for diagnosing the presence of a calculus) was 89%, the specificity 100%, the positive predictive value 100%, and the negative predictive value 81%.

CONCLUSIONS

Our data indicate that combining US with KUB provides the best diagnostic algorithm that approaches the yield of IVU in excluding the presence of a calculus in the renal-urinary tract in patients who present with intractable flank pain.

22-Oxacalcitriol does not interfere with parathyroid hormone-induced phosphaturia or cyclic-AMP excretion

The vitamin D analogue, 22-oxacalcitriol [22-oxa-1,25(OH)2 vitamin D3], has pleiotropic effects similar to or greater than calcitriol but has markedly fewer calcemic and phosphatemic effects. To test the hypothesis that the lesser phosphatemic effect of 22-oxacalcitriol is due, at least in part, to a lack of interference with the phosphaturic effect of parathyroid hormone, acute clearance experiments were performed in parathyroidectomized rats receiving continuous 1-34 parathyroid hormone (PTH) infusion together with 22-oxacalcitriol (200 pmol.100 g body weight-1.min-1) or vehicle. In contrast to the previously reported inhibitory effect of calcitriol on PTH-induced phosphaturia, fractional excretion of phosphorus increased similarly in both groups, from 0.05 +/- 0.01 to 0.26 +/- 0.02 (p < 0.01) in the vehicle-infused animals and from 0.04 +/- 0.01 to 0.24 +/- 0.02 (p < 0.01) in the 22-oxacalcitriol-treated rats (p between groups not significant [n.s.]). Urinary cyclic AMP excretion also increased similarly, from 45.5 +/- 5.2 to 101.6 +/- 21.6 (p < 0.01) and from 45.4 +/- 5.6 to 102.6 +/- 16.7 pmol/min (p < 0.01), respectively (p between groups n.s.). In search for a nongenomic mechanism that might account for the disparate effects of 22-oxacalcitriol and calcitriol, OK cells, which are reminiscent of the mammalian proximal tubule cell, were stimulated with calcitriol and 22-oxacalcitriol and free intracellular calcium concentration was determined. At high concentrations, calcitriol caused a dose-dependent increase in [Ca2+]i; 22-oxacalcitriol had no effect on [Ca2+]i at any concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

The hypotensive effect of an oral adenosine analog with selectivity for the A2 receptor in the spontaneously hypertensive rat

Adenosine is a potent arterial vasodilator that, because of a short duration of action and acid lability, is ineffective in the oral treatment of hypertension. Y-341 is a synthetic adenosine analog that is acid stable and has a prolonged duration of action. It is highly selective for the A2 receptor, which is prevalent in the vascular smooth muscle and mediates vasodilation. To determine the efficacy of Y-341 as an antihypertensive agent, the effect of Y-341 on arterial pressure was studied in spontaneously hypertensive rats (SHR) in the awake state, 3 to 4 days after arterial cannulation. Y-341 (3 mg/kg) was dissolved in 5% DMSO and administered by gavage. Blood pressure and heart rate were monitored continuously at predetermined intervals. Fifteen minutes after administration, Y-341 reduced MAP from 180 +/- 4 to 126 +/- 2 mm Hg (n = 9, P < .001). There was no significant change in heart rate. The hypotensive effect was sustained over 8 h. Vehicle (n = 5) had no effect on blood pressure. The hypotensive effect was dose dependent when the dose of Y-341 was increased from 3 to 6 and 12 mg/kg. When Y-341 was administered at 3 mg/kg/day in a single dose for 5 consecutive days, there was no significant change in the magnitude of the hypotensive response over time.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of CS-905, a novel dihydropyridine calcium channel blocker, on arterial pressure, renal excretory function, and inner medullary blood flow in the rat

CS-905 is a dihydropyridine calcium channel antagonist which stands out for its prolonged hypotensive effect, and which is currently under investigation for the treatment of hypertension. The aim of the current series of studies was to investigate the effects of CS-905 on renal function in relation to its effects on arterial pressure. In anesthetized spontaneously hypertensive rats (SHR), intravenous bolus injection of CS-905 reduced mean arterial pressure (MAP) in a dose-dependent fashion. In parallel, there was a dose-related increase in urine flow (V), sodium excretion (UNaV), renal plasma flow (RPF), and glomerular filtration rate (GFR). In chronically cannulated unanesthetized SHR, single-dose CS-905 by gavage produced a sustained reduction in MAP, a significant increase in V and UNaV, no effect on RPF, and an increase in GFR. Continuous intrarenal infusion of CS-905 in anesthetized normotensive Munich Wistar rats at doses that did not affect MAP caused a marked diuresis and natriuresis, without affecting RPF or GFR. To determine whether the diuretic and natriuretic effects of CS-905 were mediated by changes in inner medullary blood flow, the effect of CS-905 on vasa recta blood flow (Qvr) was studied by fluorescent videomicroscopy in anesthetized normotensive Munich Wistar rats during continuous intrarenal infusion. At low infusion rates, CS-905 was diuretic and natriuretic while increasing Qvr. With a high infusion rate, although the diuretic and natriuretic effects of CS-905 were maximal, Qvr decreased. These findings suggest that the diuretic and natriuretic effects of CS-905 are dissociated from and cannot be accounted for by changes in RPF, GRF, or Qvr, and are most likely secondary to a direct action of CS-905 on renal tubule handling of sodium and water.