A Cerebral and Ocular Tumor of Reticular Tissue in a Horse

An intracerebral and intraocular neoplasm occurred in a 15-year-old horse. The horse presented with signs of a cerebral space-occupying lesion, blindness, and opacity of the vitreous body. There were a number of cell types within the well-defined tumor, some of which were multinucleate, and some apparently exhibited phagocytosis. The tumor was productive of reticulin fibres. The tumor was diagnosed as a microglioma, an unusual human tumor and one not previously reported in the horse. The intraocular metastasis of the tumor is unique.

Cardiovascular MRI with ferumoxytol

The practice of contrast-enhanced magnetic resonance angiography (CEMRA) has changed significantly in the span of a decade. Concerns regarding gadolinium (Gd)-associated nephrogenic systemic fibrosis in those with severely impaired renal function spurred developments in low-dose CEMRA and non-contrast MRA as well as efforts to seek alternative MR contrast agents. Originally developed for MR imaging use, ferumoxytol (an ultra-small superparamagnetic iron oxide nanoparticle), is currently approved by the US Food and Drug Administration for the treatment of iron deficiency anaemia in adults with renal disease. Since its clinical availability in 2009, there has been rising interest in the scientific and clinical use of ferumoxytol as an MR contrast agent. The unique physicochemical and pharmacokinetic properties of ferumoxytol, including its long intravascular half-life and high r1 relaxivity, support a spectrum of MRI applications beyond the scope of Gd-based contrast agents. Moreover, whereas Gd is not found in biological systems, iron is essential for normal metabolism, and nutritional iron deficiency poses major public health challenges worldwide. Once the carbohydrate shell of ferumoxytol is degraded, the elemental iron at its core is incorporated into the reticuloendothelial system. These considerations position ferumoxytol as a potential game changer in the field of CEMRA and MRI. In this paper, we aim to summarise our experience with the cardiovascular applications of ferumoxytol and provide a brief synopsis of ongoing investigations on ferumoxytol-enhanced MR applications.

3D high-spatial-resolution cerebral MR venography at 3T: a contrast-dose-reduction study

BACKGROUND AND PURPOSE

The effect of various contrast-dose regimens for cerebral MR venography (MRV) has not been previously evaluated at 3T, to our knowledge. Our purpose was to evaluate and compare the diagnostic image quality resulting from half-versus-full-dose contrast regimens for high-spatial-resolution 3D cerebral MRV at 3T.

MATERIALS AND METHODS

Forty consecutive patients with known or suggested cerebrovascular disease underwent 3D high-spatial-resolution (0.7 x 0.6 x 0.9 mm(3)) cerebral contrast-enhanced MRV (CE-MRV) at 3T, by using an identical acquisition protocol. Patients were assigned to 1 of 2 groups: 1) full-dose (approximately 0.1 mmol/kg), and 2) half-dose (approximately 0.05 mmol/kg). Two readers evaluated the resulting images for overall image quality, venous structure definition, and arterial contamination. Signal intensity-to-noise-ratio (SNR) and contrast-to-noise-ratio (CNR) were evaluated in 8 consistent sites. Statistical analysis was performed by using Mann-Whitney U, Wilcoxon signed rank, and t tests and a kappa coefficient.

RESULTS

Both readers scored venous-structure definition as excellent or sufficient for diagnosis in approximately 90% of segments for the full-dose group (kappa = 0.87) and in approximately 80% of segments for the half-dose group (kappa = 0.85). Delineation grades were significantly lower for small venous segments, including the middle cerebral, septal, superior cerebellar, inferior vermian, posterior tonsillar, and thalamostriate veins in the half-dose group (P < .01). No significant difference existed for arterial contamination grades between the 2 groups (P > .05). SNR and CNR values were lower in the half-dose group (P < .01).

CONCLUSIONS

At 3T, high-spatial-resolution cerebral MRV can be performed with contrast doses as low as 7.5 mL, without compromising image quality as compared with full-dose protocols, except in the smallest veins, and without compromise of acquisition speed or spatial resolution.

High-resolution 3T MR angiography of the carotid arteries: comparison of manual and semiautomated quantification of stenosis

BACKGROUND AND PURPOSE

High-resolution contrast-enhanced MR angiography (CE-MRA) acquired at 3T exquisitely depict carotid artery (CA) stenosis. In this study, we examined the agreement of different vessel-analysis tools with manual quantitative measurement by 2 readers using CE-MRA data.

MATERIALS AND METHODS

Three vessel tools determining the trajectory of the vessel of interest and, subsequently, the vessel dimensions were tested against manual measurements. Diameter and area stenoses were calculated. CE-MRA data of 32 patients with CA stenosis were evaluated. The agreement between different measurements was assessed with kappa statistics after categorizing stenosis (<25%, 25%-49%, 50%-69%, 70%-99%, and 100%).

RESULTS

The mean grades of stenosis based on diameter measurements were 59% (readers) and 60%/56%/59% based on the analysis with tools A/B/C (P = 0.2-0.7). kappa values for agreement between readers and the vessel tools were 0.73/0.77/0.77 (tools A/B/C for all CAs) and 0.66/0.74/0.75 (for the symptomatic side). The mean grades of stenoses based on area measurements for tools A/B/C were 68%/63%/69% versus 58% for readers. Values from readers differed significantly from those for tools A and C (P < 0.01). kappa values for agreement between readers and the vessel tools were 0.66/0.55/0.64 (for all CAs) and 0.53/0.44/0.57 (for the symptomatic side).

CONCLUSIONS

The automated approach allows accurate assessment of vessel dimensions in MRA images at least for diameter measurements according to the North American Symptomatic Carotid Endarterectomy Trial criteria.

Assessment of craniospinal arteriovenous malformations at 3T with highly temporally and highly spatially resolved contrast-enhanced MR angiography

BACKGROUND AND PURPOSE

Patients with arteriovenous malformation (AVM) are known to have an elevated risk of complications with conventional catheter angiography (CCA) but nonetheless require monitoring of hemodynamics. Thus, we aimed to evaluate both anatomy and hemodynamics in patients with AVM noninvasively by using contrast-enhanced MR angiography (CE-MRA) at 3T and to compare the results with CCA.

MATERIALS AND METHODS

Institutional review board approval and informed consent were obtained for this Health Insurance Portability and Accountability Act-compliant study. Twenty control subjects without vascular malformation (6 men, 18-70 years of age) and 10 patients with AVMs (6 men, 20-74 years of age) underwent supra-aortic time-resolved and high-spatial-resolution CE-MRA at 3T. Large-field-of-view coronal acquisitions extending from the root of the aorta to the cranial vertex were obtained for both MRA techniques. Image quality was assessed by 2 specialized radiologists by using a 4-point scale. AVM characteristics and nidus size were evaluated by using both CE-MRA and CCA in all patients.

RESULTS

In patients, 96.6% (319/330) of arterial segments on high-spatial-resolution MRA and 87.7% (272/310) of arterial segments on time-resolved MRA were graded excellent/good. MRA showed 100% specificity for detecting feeding arteries and venous drainage (n = 8) and complete obliteration of the AVM in 2 cases (concordance with CCA). Nidus diameters measured by both MRA and CCA resulted in a very strong correlation (r = 0.99) with a mild overestimation by MRA (0.10 cm by using the Bland-Altman plot).

CONCLUSION

By combining highly temporally resolved and highly spatially resolved MRA at 3T as complementary studies, one can assess vascular anatomy and hemodynamics noninvasively in patients with AVM.

Low-dose, time-resolved, contrast-enhanced 3D MR angiography in cardiac and vascular diseases: correlation to high spatial resolution 3D contrast-enhanced MRA

AIM

To evaluate the effectiveness of low-dose, contrast-enhanced, time-resolved, three-dimensional (3D) magnetic resonance (MR) angiography (TR-MRA) in the assessment of various cardiac and vascular diseases, and to compare the results with high-resolution contrast-enhanced MRA (CE-MRA).

MATERIALS AND METHODS

Thirty consecutive patients underwent contrast-enhanced 3D TR-MRA and high spatial resolution 3D CE-MRA for evaluation of cardiac and thoracic vascular diseases at 1.5 T, and neurovascular, abdominal and peripheral vascular diseases at 3T. Gadolinium-based contrast medium was administered at a constant dose of 5 ml for TR-MRA, and 20 ml (lower extremity 30 ml) for CE-MRA. Two readers evaluated image quality using a four-point scale (from 0=excellent to 3=non-diagnostic), artefacts and findings on both datasets. Interobserver variability was tested with kappa coefficient.

RESULTS

The overall image quality for TR-MRA was in the diagnostic range (median 0, range 0-1; k=0.74). Readers demonstrated important additional dynamic information on TR-MRA in 28 of 30 patients (k=0.84). Confident evaluation of organ perfusion (n=23), arteriovenous malformation/fistula flow patterns (n=7), exclusion of intra-cardiac shunts (n=6), and assessment of stent and conduit patency (n=5) were performed by both readers using TR-MRA. Readers demonstrated fine vascular details with higher confidence in 10 patients on CE-MRA. Using CE-MRA, Reader 1 and 2 depicted anatomical details in 6 and 5 patients, respectively, only on CE-MRA.

CONCLUSION

Low-dose TR-MRA yields rapid and important functional and anatomical information in patients with cardiac and vascular diseases. Due to limited spatial resolution, TR-MRA is inferior to CE-MRA in demonstrating fine vascular details.

Contrast-enhanced MR angiography at 3T in the evaluation of intracranial aneurysms: a comparison with time-of-flight MR angiography

The combination of 3T and parallel-acquisition techniques holds promise for improved performance of contrast-enhanced MR angiography (MRA), in terms of speed, spatial resolution, and coverage. We present a comparison of 2 MRA techniques, including time-of-flight (TOF) and contrast-enhanced MRA, for detection and evaluation of intracranial aneurysms. Our results show that contrast-enhanced MRA with highly accelerated parallel acquisition at 3T does not have the known drawbacks of TOF-MRA techniques, including prolonged acquisition time, spin saturation, and flow-related artifacts, with comparable aneurysm characterization.

[Cardiac MR tagging: optimization of sequence parameters and comparison at 1.5 T and 3.0 T in a volunteer study]

PURPOSE

The aim of this study was the optimization of a gradient echo (GRE) MR tagging sequence at 3.0 T in comparison to 1.5 T in order to obtain the best image contrast between the myocardium, tag lines and blood signal. Theoretically expected improvements of signal-to-noise (SNR) and contrast-to-noise ratios (CNR) were also calculated.

MATERIALS AND METHODS

14 healthy volunteers (8 male, 6 female; mean age 43.4 +/- 10.3 years) were scanned using a 3.0 T as well as a 1.5 T whole-body system. A GRE flash-2 D tagging sequence was evaluated (midventricular short axis view) by varying the flip angle (8 - 16 degrees ), slice thickness (4 - 8 mm; fixed flip angle 1.5/3.0 T: 12 degrees /8 degrees , tag size 8 mm) and tag size (4 - 8 mm, fixed flip angle 1.5/3.0 T: 12 degrees /8 degrees , slice thickness 6 mm). The field of view, acquisition time and temporal resolution (45 ms) were kept constant. Qualitative and quantitative image analysis was performed by calculating the SNR, CNR (tag) as well as the relative contrast between the myocardium and tag lines (RCMT).

RESULTS

Based on individual comparison, the best imaging protocol was found at a slice thickness of 6 mm, tag size of 8 mm, optimized flip angle of 8 degrees (3.0 T) and 12 degrees (1.5 T), respectively. Compared to 1.5 T, a significantly higher overall image score was determined (mean +/- sd; 3.2 +/- 0.2 vs. 2.7 +/- 0.4) and a strong correlation between the CNR (tag) and RCMT for flip angle alpha and the slice thickness was found. A higher field strength resulted in an 80 % increase in the CNR (tag) compared to 1.5 T (mean 10.7/6.1). Furthermore, the SNR was improved by 35 % (mean 20.6/15.3) and the RCMT by 35 % (mean 0.47/0.35).

CONCLUSION

Myocardial tagging at 3.0 T has shown superior image quality in comparison to 1.5 T due to a higher baseline SNR and an improved CNR as well as RCMT. The suppressed fading of the tags enables the accessibility to the diastolic phase of the cardiac cycle.

The Feasibility of Spatial High-Resolution Magnetic Resonance Angiography (MRA) of the Renal Arteries at 3.0 T

PURPOSE

To evaluate the feasibility of high-spatial resolution magnetic resonance angiography (MRA) of the renal arteries at 3.0 T.

MATERIAL AND METHODS

Twelve healthy volunteers (mean age, 38.8 years) underwent renal MRA at 3.0 T. The application of parallel imaging with an acceleration factor of 3 allowed obtaining MR angiographic data with a voxel size of 0.9 x 0.8 x 0.9 mm in scan time of only 16 s. A dose of 0.2 mmol/kg body weight of 0.5-molar gadodiamide was administered at a flow rate of 2 ml/s. For image analysis, image quality, presence of artifacts, venous contamination and level of noise were rated by two radiologists in consensus.

RESULTS

All examinations were of diagnostic quality. The image quality was rated good or very good in 91 % (11/12) of cases. Due to the high parallel imaging factor the level of noise was slightly increased without diagnostic impairment. Mild venous enhancement was found in 75 % (9/12) of the examinations.

CONCLUSION

Renal MRA at 3.0 T is feasible with high spatial resolution and a short acquisition time.

Usefulness of segmented trueFISP cardiac pulse sequence in evaluation of congenital and acquired adult cardiac abnormalities

OBJECTIVE

The purpose of this study is to compare ultrashort TR, segmented trueFISP (fast imaging with steady-state precession) cine MR imaging with segmented FLASH (fast low-angle shot) cine MR imaging for the detection and characterization of congenital and acquired adult cardiac abnormalities.

SUBJECTS AND METHODS

Twenty-five patients with known or clinically suspected cardiac abnormalities were imaged on a 1.5-T scanner. Valve plane movies were obtained in patients with suspected valve morphology or function abnormalities or whose horizontal long-axis images showed jets. For each patient, three radiologists independently compared corresponding matched cine FLASH and trueFISP movies for image quality in evaluating anatomy and function of the great vessels and heart. Image quality was rated on a five-point scale, and data were analyzed using both a Wilcoxon's signed rank test and a repeated-measures analysis of variance.

RESULTS

Image quality ratings of trueFISP and FLASH showed a statistically significant difference (F = 58.67; df = 1, 72; p < 0.0001), with the average rating for the trueFISP images being significantly higher (mean rating, 4.1 +/- 0.92) than that for the FLASH images (mean, 3.0 +/- 1.0). However, valve architecture in the aortic valves appeared to be better visualized and was more easily measured in valve plane images with FLASH. No statistically significant differences among the ratings of the interpreters (F = 0.018; df = 2, 72; p = 0.9821) were evident, and, therefore, no suggestion of bias was indicated (F = 0.775; df = 1, 2; p = 0.4645). TrueFISP yielded the correct diagnosis prospectively in 13 (100%) of 13 patients, whereas FLASH yielded the correct diagnosis in 12 (92%) of 13 patients.

CONCLUSION

TrueFISP images depict morphologic and functional abnormalities with greater clarity and provide greater diagnostic confidence than FLASH images-and in a fraction of the time. A specific exception is in the assessment of valve leaflet architecture and cross-sectional area calculation (i.e., bicuspid aortic valves); in these evaluations, FLASH maintains a complementary diagnostic imaging role.

Three-dimensional MR pulmonary perfusion imaging and angiography with an injection of a new blood pool contrast agent B-22956/1

Initial evaluation of a new blood pool agent, B-22956/1, for pulmonary imaging was performed in five domestic pigs with artificial embolism. Pre-embolism 3D pulmonary perfusion images were first acquired by injecting an extravascular agent, gadoteridol. The pulmonary arteries of the pigs were then occluded by the artificial emboli. Post-embolism perfusion scans were subsequently performed by injecting B-22956/1. Additional post-embolism high-spatial-resolution angiograms were also acquired. Parenchyma perfusion deficits were well depicted in the post-embolism perfusion maps. The post-embolism angiography clearly revealed the location and extent of the filling defects in the pulmonary vessels. Signal intensities of perfusion maps on the normal parenchyma were significantly improved (30%) by using B-22956/1, in comparison with perfusion images using gadoteridol (P < 0.01). Many pulmonary angiograms with approximately equal contrast could be obtained even at 22 minutes after the injection of B-22956/1. Our initial results indicate that blood pool agent B-22956/1 may provide opportunities for whole-lung-coverage perfusion mapping and additional high-resolution target angiograms after a single injection.

Contrast-enhanced magnetic resonance angiography of the carotid circulation

Contrast-enhanced MR angiography (CE MR angiography) is rapidly becoming the investigation of first choice for evaluating disease of the vascular system. It is particularly applicable to the carotid circulation and has replaced more traditional time-of-flight imaging because of shorter acquisition times and fewer artifacts. With recent advances in gradient hardware, shorter repetition times allow high spatial resolution imaging of the entire carotid circulation form the aortic arch to the circle of Willis in less than 20 seconds. Additional acquisitions can be utilized as part of the same study to accurately time the arrival of contrast in the arterial system and overcome the problem of early venous enhancement. A number of techniques have been developed recently that allow CE MR angiography to be implemented with high temporal resolution. Both atherosclerotic and nonatherosclerotic carotid artery disease can be comprehensively assessed with CE MR angiography, preventing the need for conventional diagnostic angiography.

Contrast-enhanced coronary MR angiography: relationship between coronary artery delineation and blood T1

Contrast-enhanced coronary angiography has become an important technique for magnetic resonance (MR) coronary artery imaging. However, the relationship between the quality of the coronary artery images and blood T1 has not yet been fully explored. In this paper, we assessed this relationship in an animal model by using a prototypical blood pool agent. With accumulated injections of this agent, the blood T1 would be maintained at different levels. The measured blood T1 values in vivo were 147 +/- 3, 82 +/- 6, 48 +/- 4, 40 +/- 3, and 30 +/- 8 msec (N = 7). Fixed and variable flip angle schemes were used in coronary artery imaging. The signal to noise ratios (SNR) of coronary arteries were measured and the image quality was assessed. It was found that blood T1 less than 80 msec might be desired. No statistically significant difference was observed between two flip angle schemes. There was better vessel definition using variable flip angle at blood T1 lower than 50 msec. Understanding this relationship may be beneficial to optimizing image protocol and/or design of blood pool contrast agents for contrast-enhanced coronary angiography.

3D magnetization-prepared true-FISP: a new technique for imaging coronary arteries

The purpose of this work was to develop an ECG-triggered, segmented 3D true-FISP (fast imaging with steady-state precession) technique to improve the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of breath-hold coronary artery imaging. The major task was to optimize an appropriate magnetization preparation scheme to permit saturation of the epicardial fat signal. An alpha/2 preparation pulse was used to speed up the approach to steady-state following a frequency-selective fat-saturation pulse in each heartbeat. The application of dummy cycles was found to reduce the oscillation of the magnetization during data acquisition. The fat saturation and magnetization preparation scheme was validated with simulations and phantom studies. Volunteer studies demonstrated substantially increased SNR (55%) and CNR (178%) for coronary arteries compared to FLASH (fast low-angle shot) with the same imaging time. In conclusion, true-FISP is a promising technique for coronary artery imaging.

Assessment of regional differences in myocardial blood flow using T2-weighted 3D BOLD imaging

The feasibility of detecting regional differences in myocardial blood flow based on the blood oxygen level-dependent (BOLD) effect was evaluated in vivo in dogs (N = 9) using a 3D T2-prepared segmented gradient-echo sequence at 1.5 T. Regional differences in myocardial blood flow were created by administering adenosine through a catheter placed in the left circumflex coronary artery (LCX). The difference in the R2 (1/T2) relaxation rate between the left ventricular myocardial region supplied by the LCX and regions supplied by the left anterior descending coronary artery (LAD) or septal artery during adenosine administration was correlated to the corresponding regional myocardial blood flow difference determined using fluorescent microspheres. A correlation coefficient of 0.80 was found between the MR BOLD measurements and the myocardial flow assessment. Our results show that the sequence used in this study allows fast 3D BOLD imaging of the heart, and is a promising technique for detecting regional myocardial perfusion differences.

Cep-1347 (KT7515), a semisynthetic inhibitor of the mixed lineage kinase family

CEP-1347 (KT7515) promotes neuronal survival at dosages that inhibit activation of the c-Jun amino-terminal kinases (JNKs) in primary embryonic cultures and differentiated PC12 cells after trophic withdrawal and in mice treated with 1-methyl-4-phenyl tetrahydropyridine. In an effort to identify molecular target(s) of CEP-1347 in the JNK cascade, JNK1 and known upstream regulators of JNK1 were co-expressed in Cos-7 cells to determine whether CEP-1347 could modulate JNK1 activation. CEP-1347 blocked JNK1 activation induced by members of the mixed lineage kinase (MLK) family (MLK3, MLK2, MLK1, dual leucine zipper kinase, and leucine zipper kinase). The response was selective because CEP-1347 did not inhibit JNK1 activation in cells induced by kinases independent of the MLK cascade. CEP-1347 inhibition of recombinant MLK members in vitro was competitive with ATP, resulting in IC(50) values ranging from 23 to 51 nm, comparable to inhibitory potencies observed in intact cells. In addition, overexpression of MLK3 led to death in Chinese hamster ovary cells, and CEP-1347 blocked this death at doses comparable to those that inhibited MLK3 kinase activity. These results identify MLKs as targets of CEP-1347 in the JNK signaling cascade and demonstrate that CEP-1347 can block MLK-induced cell death.

An improved MR imaging technique for the visualization of myocardial infarction

PURPOSE

To design a segmented inversion-recovery turbo fast low-angle shot (turboFLASH) magnetic resonance (MR) imaging pulse sequence for the visualization of myocardial infarction, compare this technique with other MR imaging approaches in a canine model of ischemic injury, and evaluate its utility in patients with coronary artery disease.

MATERIALS AND METHODS

Six dogs and 18 patients were examined. In dogs, infarction was produced and images were acquired by using 10 different pulse sequences. In patients, the segmented turboFLASH technique was used to acquire contrast material-enhanced images 19 days +/- 7 (SD) after myocardial infarction.

RESULTS

Myocardial regions of increased signal intensity were observed in all animals and patients at imaging. With the postcontrast segmented turboFLASH sequence, the signal intensity of the infarcted myocardium was 1,080% +/- 214 higher than that of the normal myocardium in dogs-nearly twice that of the next best sequence tested and approximately 10-fold greater than that in previous reports. All 18 patients with myocardial infarction demonstrated high signal intensity at imaging. On average, the signal intensity of the high-signal-intensity regions in patients was 485% +/- 43 higher than that of the normal myocardium.

CONCLUSION

The segmented inversion-recovery turboFLASH sequence produced the greatest differences in regional myocardial signal intensity in animals. Application of this technique in patients with infarction substantially improved differentiation between injured and normal regions.

Cine MR Angiography of the Heart with Segmented True Fast Imaging with Steady-State Precession

In five healthy subjects and 18 patients, cine magnetic resonance (MR) imaging of the heart was performed with a true fast imaging with steady-state precession (FISP) sequence. Results were compared both quantitatively and qualitatively with those at cine fast low-angle shot (FLASH) MR imaging. The blood-myocardial contrast-to-noise ratio (CNR) was 2.0 times higher and the normalized (for measurement time and pixel size) blood-myocardial CNR was 4.0 times higher for true FISP compared with FLASH MR imaging. Qualitative scores for image quality were significantly higher with true FISP MR imaging. Segmented cine true FISP MR imaging generated high-contrast MR images of the heart in healthy subjects and in patients with heart disease and produced image quality superior to that with cine FLASH MR imaging.

Coronary arteries: magnetization-prepared contrast-enhanced three-dimensional volume-targeted breath-hold MR angiography

A volume-targeted contrast agent-enhanced breath-hold coronary magnetic resonance angiographic technique was optimized and evaluated in 16 volunteers. Substantial increases in coronary signal-to-noise ratio, contrast-to-noise ratio, lengths of depiction, and vessel sharpness were observed on enhanced images. The imaging approach with two 20-mL injections of contrast agent covers the left and right coronary arteries in two breath holds and is a promising method for coronary imaging.

Effect of creatine supplementation on metabolism and performance in humans during intermittent sprint cycling

This double blind study investigated the effect of oral creatine supplementation (CrS) on 4 x 20 s of maximal sprinting on an air-braked cycle ergometer. Each sprint was separated by 20 s of recovery. A group of 16 triathletes [mean age 26.6 (SD 5.1) years. mean body mass 77.0 (SD 5.8) kg, mean body fat 12.9 (SD 4.6)%, maximal oxygen uptake 4.86 (SD 0.7) l.min-1] performed an initial 4 x 20 s trial after a muscle biopsy sample had been taken at rest. The subjects were then matched on their total intramuscular creatine content (TCr) before being randomly assigned to groups to take by mouth either a creatine supplement (CRE) or a placebo (CON) before a second 4 x 20 s trial. A muscle biopsy sample was also taken immediately before this second trial. The CrS of 100 g comprised 4 x 5 g for 5 days. The initial mean TCr were 112.5 (SD 8.7) and 112.5 (SD 10.7) mmol.kg-1 dry mass for CRE and CON, respectively. After creatine loading and placebo ingestion respectively, CRE [128.7 (SD 11.8) mmol.kg-1 dry mass] had a greater (P = 0.01) TCr than CON [112.0 (SD 10.0) mmol.kg-1 dry mass]. While the increase in free creatine for CRE was statistically significant (P = 0.034), this was not so for the changes in phosphocreatine content [trial 1: 75.7 (SD 6.9), trial 2: 84.7 (SD 11.0) mmol.kg-1 dry mass, P = 0.091]. There were no significant differences between CRE and CON for citrate synthase activity (P = 0.163). There was a tendency towards improved performance in terms of 1 s peak power (in watts P = 0.07; in watts per kilogram P = 0.05), 5 s peak power (in watts P = 0.08) and fatigue index (P = 0.08) after CrS for sprint 1 of the second trial. However, there was no improvement for mean power (in watts P = 0.15; in watts per kilogram P = 0.1) in sprint 1 or for any performance values in subsequent sprints. Our results suggest that, while CrS elevates the intramuscular stores of free creatine, this does not have an ergogenic effect on 4 x 20 s all-out cycle sprints with intervening 20-s rest periods.

Coronary artery imaging: 3D segmented k-space data acquisition with multiple breath-holds and real-time slab following

The purpose of this work was to develop a multiple-breath-hold (BH) imaging method for coronary arteries in which a segment of k-space is acquired in each BH. The goal was to increase the resolution, or the signal-to-noise ratio (SNR) and coverage, of three-dimensional-(3D)-BH volume-targeted scanning (VCATS). To correct for slab position differences, a real-time slab following technique using navigator echoes for motion detection was used. Sixteen normal volunteers were imaged to compare the method with a single-BH scan. Results showed that higher resolution, or larger coverage and higher SNR, were achieved by the multiple-BH method without respiratory motion artifacts. In conclusion, 3D segmented k-space data acquisition with multiple-BHs and real-time slab following is a promising approach for extending the capabilities of VCATS further.

An improved MR imaging technique for the visualization of myocardial infarction

PURPOSE

To design a segmented inversion-recovery turbo fast low-angle shot (turboFLASH) magnetic resonance (MR) imaging pulse sequence for the visualization of myocardial infarction, compare this technique with other MR imaging approaches in a canine model of ischemic injury, and evaluate its utility in patients with coronary artery disease.

MATERIALS AND METHODS

Six dogs and 18 patients were examined. In dogs, infarction was produced and images were acquired by using 10 different pulse sequences. In patients, the segmented turboFLASH technique was used to acquire contrast material-enhanced images 19 days +/- 7 (SD) after myocardial infarction.

RESULTS

Myocardial regions of increased signal intensity were observed in all animals and patients at imaging. With the postcontrast segmented turboFLASH sequence, the signal intensity of the infarcted myocardium was 1,080% +/- 214 higher than that of the normal myocardium in dogs-nearly twice that of the next best sequence tested and approximately 10-fold greater than that in previous reports. All 18 patients with myocardial infarction demonstrated high signal intensity at imaging. On average, the signal intensity of the high-signal-intensity regions in patients was 485% +/- 43 higher than that of the normal myocardium.

CONCLUSION

The segmented inversion-recovery turboFLASH sequence produced the greatest differences in regional myocardial signal intensity in animals. Application of this technique in patients with infarction substantially improved differentiation between injured and normal regions.

Air-braked cycle ergometers: validity of the correction factor for barometric pressure

Barometric pressure exerts by far the greatest influence of the three environmental factors (barometric pressure, temperature and humidity) on power outputs from air-braked ergometers. The barometric pressure correction factor for power outputs from air-braked ergometers is in widespread use but apparently has never been empirically validated. Our experiment validated this correction factor by calibrating two air-braked cycle ergometers in a hypobaric chamber using a dynamic calibration rig. The results showed that if the power output correction for changes in air resistance at barometric pressures corresponding to altitudes of 38, 600, 1,200 and 1,800 m above mean sea level were applied, then the coefficients of variation were 0.8-1.9% over the range of 160-1,597 W. The overall mean error was 3.0 % but this included up to 0.73 % for the propagated error that was associated with errors in the measurement of: a) temperature b) relative humidity c) barometric pressure d) force, distance and angular velocity by the dynamic calibration rig. The overall mean error therefore approximated the +/- 2.0% of true load that was specified by the Laboratory Standards Assistance Scheme of the Australian Sports Commission. The validity of the correction factor for barometric pressure on power output was therefore demonstrated over the altitude range of 38-1,800 m.

A carcinogenicity study of sucralose in the CD-1 mouse

The potential carcinogenicity of sucralose was evaluated by feeding groups of 52 male and 52 female CD-1 mice a diet containing sucralose at 0.3% (3000 ppm), 1.0% (10,000 ppm) or 3.0% (30,000 ppm) for 104 weeks. A group of 72 male and 72 female mice received diet without sucralose and served as controls. Week 1 achieved doses ranging from 543 to 5870mg/kg body weight/day in the low-dose males and high-dose females, respectively. Sucralose had no adverse effect on survival. No significant changes attributable to sucralose were found in the clinical condition or behaviour of the mice. Organ weights and the gross appearance of tissues were unaffected by treatment. The mean erythrocyte counts of females receiving the highest dietary concentration were slightly, but statistically significantly, lower than those of the controls after 104 weeks of treatment. Group mean body weight gain at the highest dietary concentration of sucralose was significantly less than that of the control in mice of both sexes. Food consumption, after correction for sucralose content, was lower for female mice, but not statistically significant. Water consumption for male mice receiving the highest dietary concentration was approximately 9% higher than that of the controls. There were statistically significant increases in the incidence of several non-neoplastic findings, but these were not considered to be related to sucralose administration. Treatment with sucralose did not increase the incidence of any tumour or influence the types of tumours observed. It was concluded that sucralose is not carcinogenic in CD-1 mice. The body weight gain and erythrocyte observations at the 3.0% dietary level were of limited biological significance as they were not accompanied by any histopathologic finding and had no impact on survival. The remaining dose levels were judged to have no effects.

A combined chronic toxicity/carcinogenicity study of sucralose in Sprague-Dawley rats

The chronic toxicity and potential carcinogenicity of sucralose was evaluated by exposing Sprague-Dawley rats to dietary concentrations of this low-calorie sweetener both in utero and for up to 104 weeks following parturition. The rats assigned to the toxicity phase of this investigation were administered diets containing either 0% (control), 0.3% (3000 ppm), 1.0% (10,000 ppm) or 3.0% (30,000 ppm) sucralose. Each treatment group comprised 30 male and 30 female rats, of which 15 males and 15 females were sacrificed after 52 weeks of treatment. The surviving rats were killed following 78 weeks of sucralose administration. In the carcinogenicity phase of this investigation, groups of 50 male and 50 female rats were administered dietary sucralose at concentrations of 0% (control 1), 0% (control 2), 0.3%, 1.0% or 3.0% for 104 weeks. Evaluation of the data obtained from the two phases of this study showed that sucralose was not carcinogenic. Sucralose did not adversely affect the survival or clinical condition of the rats, and there were no toxicologically significant findings. Group mean body weight gain and food consumption were significantly decreased in a dose-dependent manner in sucralose-treated rats throughout the treatment period as compared to the controls. The primary effect of sucralose on food consumption, and secondarily on body weight gain, was established in later studies to be due to the fact that diets containing high concentrations of sucralose are unpalatable to rats. These subsequent studies established that the reduction of body weight gain seen in previous rat studies using sucralose in the diet at concentrations of 1% and below resulted from reduced food intake as a direct consequence of the unpalatable nature of sucralose. Similarly, at concentrations of 3% in the diet, it was shown that approximately 95% of the effect on body weight gain could be attributed to the reduction in food intake due to the reduced palatability of the diet, the remainder apparently due to a physiologic response to the high concentrations of non-digestible sucralose in the rats' diet. Complete toxicological evaluations of gavage studies with histopathological evaluations demonstrated that even at the 3% dietary level, toxicity was not responsible for the small body weight gain decrement. Gross and histopathologic examinations revealed that the administration of sucralose affected neither the types nor incidence of the tumours observed. The incidences of some non-neoplastic findings were statistically significantly increased in the sucralose treated groups relative to the controls. These included: renal pelvic epithelial hyperplasia in all female treatment groups, renal pelvic mineralization in females administered the intermediate or highest dietary concentrations of sucralose, adrenal cortical haemorrhagic degeneration in high-dose group female rats, and the histopathologic incidence of cataracts at necropsy in high-dose group male rats. The non-neoplastic findings that occurred were of no toxicological significance since they were either spontaneous findings commonly observed in aged rats of this strain or the physiological response to high dietary levels of a poorly absorbed compound.

Neurotoxicity studies on sucralose and its hydrolysis products with special reference to histopathologic and ultrastructural changes

Comparative neuropathological studies of 1,6-dichloro-1, 6-dideoxy-beta-D-fructofuranosyl-4-chloro-4-deoxy-alpha-D-galactopyra noside (sucralose), an equimolar mixture of 1,6-dichloro-1, 6-dideoxyfructose (1,6-DCF) and 4-chloro-4-deoxygalactose (4-CG), the hydrolysis products of sucralose, and 6-chloro-6-deoxyglucose (6-CG) were conducted in male and female mice and male marmoset monkeys, focusing on morphological changes in the central nervous system. 6-Chloro-6-deoxyglucose, previously reported to produce neurotoxic effects, served as the positive control and was administered by gavage at a daily dose of 500mg/kg. Sucralose and the sucralose hydrolysis products (sucralose-HP) were similarly administered to mice and marmosets at doses of up to 1000mg/kg for 21 and 28 days, respectively. No changes were detected in the central nervous system by light or electron microscopy in either of the species that received sucralose or its hydrolysis products. 6-Chloro-6-deoxyglucose, in contrast, induced symmetrical lesions in the deep nuclei of the cerebellum, brain stem and spinal cord with definitive neurological signs of CNS involvement.

Relationship of MRI delayed contrast enhancement to irreversible injury, infarct age, and contractile function

BACKGROUND

Contrast MRI enhancement patterns in several pathophysiologies resulting from ischemic myocardial injury are controversial or have not been investigated. We compared contrast enhancement in acute infarction (AI), after severe but reversible ischemic injury (RII), and in chronic infarction.

METHODS AND RESULTS

In dogs, a large coronary artery was occluded to study AI and/or chronic infarction (n = 18), and a second coronary artery was chronically instrumented with a reversible hydraulic occluder and Doppler flowmeter to study RII (n = 8). At 3 days after surgery, cine MRI revealed reduced wall thickening in AI (5+/-6% versus 33+/-6% in normal, P<0.001). In RII, wall thickening before, during, and after inflation of the occluder for 15 minutes was 35+/-5%, 1+/-8%, and 21+/-10% and Doppler flow was 19.8+/-5.3, 0.2+/-0.5, and 56.3+/-17.7 (peak hyperemia) cm/s, respectively, confirming occlusion, transient ischemia, and reperfusion. Gd-DTPA-enhanced MR images acquired 30 minutes after contrast revealed hyperenhancement of AI (294+/-96% of normal, P<0.001) but not of RII (98+/-6% of normal, P = NS). Eight weeks later, the chronically infarcted region again hyperenhanced (253+/-54% of normal, n = 8, P<0.001). High-resolution (0.5 x 0.5 x 0.5 mm) ex vivo MRI demonstrated that the spatial extent of hyperenhancement was the same as the spatial extent of myocyte necrosis with and without reperfusion at 1 day (R = 0.99, P<0.001) and 3 days (R = 0.99, P<0.001) and collagenous scar at 8 weeks (R = 0.97, P<0.001).

CONCLUSIONS

In the pathophysiologies investigated, contrast MRI distinguishes between reversible and irreversible ischemic injury independent of wall motion and infarct age.

CEP-1347 (KT7515), an inhibitor of JNK activation, rescues sympathetic neurons and neuronally differentiated PC12 cells from death evoked by three distinct insults

The c-Jun N-terminal kinase signaling cascade appears to play a role in some cases of cell death, including neuronal apoptosis. CEP-1347 (KT7515), an indolocarbazole of the K252a family, blocks this stress signaling cascade and promotes survival. Here, we used CEP-1347 to probe whether neuronal death pathways activated by distinct insults also possess elements in common. Cultured rat sympathetic neurons and neuronally differentiated PC12 cells were induced to die by withdrawal of nerve growth factor, exposure to ultraviolet irradiation, or subjection to oxidative stress. In each case, death was prevented by 100-200 nM CEP-1347. Moreover, in each of these death paradigms, c-Jun N-terminal kinase 1 activity in neuronally differentiated PC12 cells was elevated by two- or threefold, and this increase was totally blocked by CEP-1347 at concentrations that promoted survival. In contrast, 200 nM CEP-1347 did not block death due to serum withdrawal from undifferentiated PC12 cells or to activation of Fas in Jurkat T cell cultures, even though in each case c-Jun N-terminal kinase 1 activation occurred and was inhibited by CEP-1347. These observations suggest that some but not all death pathways triggered by different insults can include a common mechanistic component, a likely candidate for which is activation of the c-Jun N-terminal kinase signaling cascade.

Immunolocalization of the mitogen-activated protein kinases p42MAPK and JNK1, and their regulatory kinases MEK1 and MEK4, in adult rat central nervous system

Cell survival, death, and stress signals are transduced from the cell surface to the cytoplasm and nucleus via a cascade of phosphorylation events involving the mitogen-activated protein kinase (MAPK) family. We compared the distribution of p42 mitogen-activated protein kinase (p42MAPK) and its activator MAPK or ERK kinase (MEK1; involved in transduction of growth and differentiation signals), with c-Jun N-terminal kinase (JNK1) and its activator MEK4 (involved in transduction of stress and death signals) in the adult rat central nervous system. All four kinases were present in the cytoplasm, dendrites, and axons of neurons. The presence of p42MAPK and JNK1 in dendrites and axons, as well as in cell bodies, suggests a role for these kinases in phosphorylation and regulation of cytoplasmic targets. A high degree of correspondence was found between the regional distribution of MEK1 and p42MAPK. Immunostaining for MEK1 and p42MAPK was intense in olfactory structures, neocortex, hippocampus, striatum, midline, and interlaminar thalamic nuclei, hypothalamus, brainstem, Purkinje cells, and spinal cord. In addition to neurons, p42MAPK was also present in oligodendrocytes. Whereas MEK4 was ubiquitously distributed, JNK1 was more selective. Immunostaining for MEK4 and JNK1 was intense in the olfactory bulb, lower cortical layers, the cholinergic basal forebrain, most nuclei of the thalamus, medial habenula, and cranial motor nuclei. The distribution of MEK1 and p42MAPK proteins only partially overlapped with that of MEK4 and JNK1. This suggests that the growth/differentiation and death/stress pathways affected by these kinases may not necessarily act to counterbalance each other in response to extracellular stimuli. The differential distribution of these kinases may control the specificity of neuronal function to extracellular signals.

Multiple residues contribute independently to differences in ligand recognition between vesicular monoamine transporters 1 and 2

The two closely related vesicular monoamine transporters (VMATs) 1 and 2 differ substantially in ligand recognition. The neuronal VMAT2 exhibits a higher affinity for monoamine substrates and in particular for histamine as well as a greater sensitivity to the inhibitor tetrabenazine than the nonneuronal VMAT1. The analysis of chimeric transport proteins has previously shown that two major domains, one spanning transmembrane domains (TMDs) 5-8 (TMD5-8) and the other, TMDs 9-12 (TMD9-12), are required for the high affinity interactions characteristic of VMAT2. Using site-directed mutagenesis to replace residues in TMD5-8 of VMAT2 with the equivalent residues from VMAT1, we now show that the sensitivity of VMAT2 to tetrabenazine requires Ala-315, and this interaction occurs independently of the interaction with residues in TMD9-12. The ability to recognize histamine as a substrate depends on Pro-237, and the contribution of TMD9-12 to histamine recognition appears to involve a common mechanism. In contrast, the replacement of many residues in TMD5-8 of VMAT2 with equivalent residues from VMAT1 improves the recognition of both serotonin and tryptamine, and these mutations show a dominant effect on the recognition of both tryptamine and serotonin over mutations in TMD9-12. The results indicate that different ligands interact through distinct mechanisms with the VMATs and that the recognition of each ligand involves multiple, independent interactions with the transport protein.

Region-specific targets of p42/p44MAPK signaling in rat brain

In vitro studies indicate that p42/p44MAPK phosphorylate both nuclear and cytoplasmic proteins. However, the functional targets of p42/p44MAPK activation in vivo remain unclear. To address this question, we localized activated p42/p44MAPK in hippocampus and cortex and determined their signaling effects after electroconvulsive shock treatment (ECT) in rats. Phosphorylated p42/p44MAPK content increased in the cytoplasm of hippocampal neurons in response to ECT. Consistent with this cytoplasmic localization, inhibition of ECT-induced p42/p44MAPK activation by the extracellular signal-regulated kinase kinase inhibitor PD098059 blocked phosphorylation of the cytoplasmic protein microtubule-associated protein 2c (MAP2c), but failed to inhibit the induction of the nuclear protein c-Fos in response to ECT. In contrast to hippocampal neurons, cortical neurons exhibited an increase in amount of phosphorylated p42/p44MAPK in both the nucleus and cytoplasm after ECT. Accordingly, PD098059 blocked the induction of Fos-like immunoreactivity in the nuclei of cortical neurons as well as MAP2c phosphorylation in the cytoplasm. Our data indicate that both nuclear and cytoplasmic substrates can be activated by p42/p44MAPK in vivo. However, the functional targets of p42/p44MAPK signaling depend on the precise location of p42/p44MAPK within different subcellular compartments of brain regions. These results indicate unique functional pathways of p42/p44MAPK-mediated signal transduction within different brain regions in vivo.

Motoneuron apoptosis is blocked by CEP-1347 (KT 7515), a novel inhibitor of the JNK signaling pathway

Neurons undergoing apoptosis can be rescued by trophic factors that simultaneously increase the activity of extracellular signal-regulated kinase (ERK) and decrease c-Jun N-terminal kinase (JNK) and p38. We identified a molecule, CEP-1347 (KT7515), that rescues motoneurons undergoing apoptosis and investigated its effect on ERK1 and JNK1 activity. Cultured rat embryonic motoneurons, in the absence of trophic factor, began to die 24-48 hr after plating. During the first 24 hr ERK1 activity was unchanged, whereas JNK1 activity increased fourfold. CEP-1347 completely rescued motoneurons for at least 72 hr with an EC50 of 20 +/- 2 nM. CEP-1347 did not alter ERK1 activity but rapidly inhibited JNK1 activation. The IC50 of CEP-1347 for JNK1 activation was the same as the EC50 for motoneuron survival. Inhibition of JNK1 activation by CEP-1347 was not selective to motoneurons. CEP-1347 also inhibited JNK1 activity in Cos7 cells under conditions of ultraviolet irradiation, osmotic shock, and inhibition of glycosylation. Inhibition by CEP-1347 of the JNK1 signaling pathway appeared to be selective, because CEP-1347 did not inhibit p38-regulated mitogen-activated protein kinase-activated protein kinase-2 (MAPKAP2) activity in Cos7 cells subjected to osmotic shock. The direct molecular target of CEP-1347 was not JNK1, because CEP-1347 did not inhibit JNK1 activity in Cos7 cells cotransfected with MEKK1 and JNK1 cDNA constructs. This is the first demonstration of a small organic molecule that promotes motoneuron survival and that simultaneously inhibits the JNK1 signaling cascade.

Individual residues contribute to multiple differences in ligand recognition between vesicular monoamine transporters 1 and 2

Molecular cloning has identified two vesicular monoamine transporters (VMATs), one expressed in non-neural cells of the periphery (VMAT1) and the other by multiple monoamine cell populations in the brain (VMAT2). Functional analysis has previously shown that VMAT2 has a higher affinity than VMAT1 for monoamine neurotransmitters as well as the inhibitor tetrabenazine. The analysis of chimeric transporters has also identified two major regions required for the high affinity interactions of VMAT2 with these ligands. We have now used site-directed mutagenesis to identify the individual residues responsible for these differences. Focusing on the region that spans transmembrane domains 9 through 12, we have replaced VMAT2 residues with the corresponding residues from VMAT1. Many residues in this region had no effect on the recognition of these ligands, but substitution of Tyr-434 with Phe and Asp-461 with Asn reduced the affinity for tetrabenazine, histamine, and serotonin. Although the ability to affect recognition of multiple ligands suggests a general structural role for these residues, the mutations did not affect dopamine recognition, indicating a more specific role, possibly in recognition of the ring nitrogen that occurs in tetrabenazine, histamine, and serotonin but not dopamine. The mutation K446Q reduced the affinity of VMAT2 for tetrabenazine and serotonin but not histamine, whereas F464Y reduced serotonin affinity and perhaps histamine recognition but not tetrabenazine sensitivity, providing more evidence for specificity. Interestingly, the Vmax of both VMATs for dopamine exceeded that for serotonin by 3-5-fold, indicating a difference in the speed of packaging of these two neurotransmitters. We also found that VMAT1 has a higher affinity for tryptamine than VMAT2. This mutually exclusive interaction with serotonin and tryptamine also suggests a physiological rationale for the existence of two VMATs. Surprisingly, the residue responsible for this difference, Tyr-434, also accounts for the higher affinity interaction of VMAT2 with tetrabenazine, histamine, and serotonin. Interestingly, replacement of Tyr-434 with alanine increases the affinity of VMAT2 for both serotonin and dopamine and reduces the rate of dopamine transport.

Effect of muscle glycogen availability on maximal exercise performance

This investigation determined the influence of pre-exercise muscle glycogen availability on performance during high intensity exercise. Nine trained male cyclists were studied during 75 s of all-out exercise on an air-braked cycle ergometer following muscle glycogen-lowering exercise and consumption of diets (energy content approximately 14 MJ) that were either high (HCHO(80% CHO) or low (LCHO-25% CHO) in carbohydrate content. The exercise-diet regimen was successful in producing differences in pre-exercise muscle glycogen contents [HCHO: 578(SEM 55) mmol x kg(-1) dry mass; LCHO: 364 (SEM 58) P < 0.05 mmol x kg(-1) dry mass]. Despite this difference in muscle glycogen availability, there were no between trial differences for peak power [HCHO 1185 (SEM 50)W, LCHO 1179 (SEM 48)W], mean power [HCHO 547 (SEM 5)W, LCHO 554 (SEM 8)W] and maximal accumulated oxygen deficit [HCHO 54.4 (SEM 2.3) ml x kg(-1), LCHO 54.6 (SEM 2.0) ml x kg(-1)]. Postexercise muscle lactate contents (HCHO 95.9 (SEM 4.6) mmol x kg(-1) dry mass, LCHO 82.7 (SEM 12.3) mmol x kg(-1) dry mass, n = 8] were no different between the two trials, nor were venous blood lactate concentrations immediately after and during recovery from exercise. These results would indicate that increased muscle glycogen availability has no direct effect on performance during all-out high intensity exercise.

Magnetic resonance angiography demonstration of congenital heart disease in adults

OBJECTIVE

There are limitations when using spin-echo MR imaging to evaluate congenital heart disease (CHD). These include limited ability to detect small shunts, long acquisition times, in-plane or slow flow signal and limited ability to represent complicated three-dimensional (3D) anatomy. However, MR angiography can image flow direction and disturbances, assess function and easily represents 3D anatomy. This may be valuable when evaluating adults with CHD.

PATIENTS AND METHODS

Fifty consecutive adult patients were referred for MR evaluation of possible or known CHD using time-of-flight MR angiography. Cine, breathhold and presaturation cine MR angiography were acquired as appropriate, with 3D (MIP) reconstruction of all extracardiac anomalies.

RESULTS

Forty-nine patients had a diagnostic examination (one was unsatisfactory because of arrhythmia). Correlation with alternative imaging (TTE = 36, TOE = 13, cardiac catheter = 16) or surgery was available in 39 patients (MR angiography correct in 36 patients). MRA demonstrated or excluded all confirmed congenital valve (12/12), aortic (9/9), and venous (7/7) anomalies. Thirty-five patients were evaluated for shunts. MR angiography detected 31/33 confirmed shunts (shunts present in 26 patients, sensitivity 94%, specificity 95%). Although not used in all cases, spin-echo was unreliable in demonstrating shunts as signal loss in the region of the secundum septum frequently mimicked atrial septal defects (reducing accuracy for excluding intracardiac shunts, specificity 58%).

CONCLUSION

MR angiography accurately defines intra- and extra-cardiac anatomy and is superior to spin-echo in detecting or excluding shunts. MR angiography safely and accurately demonstrates many aspects of CHD in adults.

First-pass evaluation of myocardial output during dipyridamole stress using turbo-FLASH magnetic resonance imaging

RATIONALE AND OBJECTIVES

This study evaluated the value of dynamically enhanced fast low-angle shot (FLASH) magnetic resonance (MR) imaging in measuring cardiac output with and without dipyridamole pharmacological stress.

METHODS

Ten subjects underwent rest and stress MR imaging. Rest images were acquired using electrocardiogram gated MR (turbo-FLASH: repetition time = 6 mseconds; echo time = 12 mseconds; flip angle = 12 degrees, inversion time = 100) 10 to 45 seconds after intravenous bolus of 0.04 mmol/kg gadolinium (Gd)-DTPA using a Siemens 1.0-tesla Magnetom SP. Stress was induced within the MR imaging scanner with 0.56 mg/kg dipyridamole over 4 minutes with stress MR images obtained after a second bolus of Gd-DTPA in exactly the same position and time intervals. Cardiac output was calculated with a least squares error analysis before and after dipyridamole stress for the left and right ventricles in all 10 patients, and comparison was made with cardiac output by Fick dilution technique during cardiac catheterization in seven patients.

RESULTS

This MR analysis methodology shows reasonable correlation (r = 0.953) between left ventricular and right ventricular cardiac output with no effect on cardiac output during immediate dipyridamole stress. Fick dilution studies demonstrated a correlation of 0.96.

CONCLUSIONS

Turbo-FLASH MR can demonstrate time-activity curves and cardiac output calculations consistent with theoretical predictions.

A macro-driven Excel template for determining the anaerobic capacity using an air-braked ergometer

This paper describes a microcomputer system for automating the process of data collection, calculation and display of anaerobic capacity tests on an air-braked ergometer. The use of the spreadsheet Excel and associated 'Dalog' program represents an advance on current software which estimates the anaerobic capacity from work performed alone. Numerous calculations are required when air-braked, rather than friction-braked erogometers are used. Each 1 s power output collected during an all-out sprint on the ergometer is corrected against the criterion of a dynamic calibration rig and adjusted for differences in barometric pressure, ambient temperature and humidity. The Excel template features a series of macros invoked by buttons imbedded in the spreadsheet. Their selection displays various dialogue boxes which request input related to the calculation of oxygen deficit and related variables. Selecting the final macro prints a summary table and charts which include: power output, fatigue index, mechanical work performed, % aerobic contribution to work, oxygen demand, oxygen consumption and anaerobic capacity as determined by the maximal accumulated oxygen deficit.

Liver masses: replacement of conventional T2-weighted spin-echo MR imaging with breath-hold MR imaging

PURPOSE

To evaluate breath-hold magnetic resonance (MR) imaging with single-shot and multishot T2-weighted fast spin-echo (SE) and inversion-recovery (IR) SE echo-planar (EP) SE (IR-SE-EP) sequences compared with conventional T2-weighted SE imaging for detection of liver masses.

MATERIALS AND METHODS

Imaging with all sequences was performed in 32 patients on a 1.5-T whole-body system. Images were compared on the basis of lesion-to-liver contrast-to-noise ratio (C/N), lesion conspicuity, and image quality. Image analysis was performed by two experienced radiologists in consensus.

RESULTS

Lesion-to-liver C/Ns were highest on fat-suppressed-half-Fourier-single-shot-fast-SE images. For solid lesions, the lesion-to-liver C/Ns were highest with IR-fast-SE, which was significantly better (P < .05) than IR-SE-EP and conventional SE techniques and also produced the best image quality. Sensitivity with IR-fast-SE was 96%; with fat-suppressed-half-Fourier-single-shot-fast-SE, 92%; with fat-suppressed-fast-SE, 89%; with IR-SE-EP, 83%; and with conventional SE, 78%.

CONCLUSION

T2-weighted breath-hold imaging, particularly IR-fast-SE imaging, was more sensitive for hepatic masses than conventional SE imaging, with a substantial reduction in acquisition time. Half-Fourier-single-shot-fast-SE imaging was especially useful in patients who were unable to hold their breath.

MR perfusion imaging of the kidney pre- and post-dipyridamole stress

Animal studies have demonstrated that renal MR contrast enhancement depends on the timing of image acquisition. Limited human studies have demonstrated effects of dipyridamole (DP) on total renal perfusion. This study assessed the effect of DP on total and regional renal perfusion using gated perfusion MRI for patients undergoing DP stress. Five subjects with no evidence of renal ischemia were examined at rest and after DP stress. Rest MRI images in the left kidney were acquired using electrocardiogram (ECG)-gated MR: turbo fast low-angle shot (FLASH); echo time (TE) = 12, repetition time (TR) = 6, flip angle = 12, inversion time (TI) = 100) 10 to 45 seconds after injection of gadopentetate dimeglumine. Stress was induced in the MRI scanner (DP, .56 mg/kg over 4 minutes) followed by stress MRI after a second bolus of gadopentetate dimeglumine in the same position and identical time intervals. MR signal in the whole left kidney and renal medulla and cortex pre- and post-DP demonstrated a 70% depression of total renal perfusion with relative preservation of cortical perfusion at the expense of medullary perfusion. Post-DP MR images demonstrated a decrease in cortical perfusion with an additional 29% depression of medullary perfusion (P < .001) with respect to cortical perfusion. Turbo FLASH MRI can provide adequate time and spatial resolution to demonstrate changes in renal perfusion. Depression of renal medullary perfusion after DP appears to be caused by the intrarenal effect of DP and may have clinical impact.