CT Angiography of the Renal Arteries: Comparison of Lower-Tube-Voltage CTA With Moderate-Concentration Iodinated Contrast Material and Conventional CTA

Validation of computed tomography angiography as a complementary test in the assessment of renal artery stenosis: a comparison with digital subtraction angiography

BACKGROUND

Renal artery stenosis is an important cause of hypertension in children, accounting for 5-10% of cases. When suspected, noninvasive imaging options include ultrasound (US), computed tomography (CT) angiography and magnetic resonance (MR) angiography. However, digital subtraction angiography (DSA) remains the gold standard.

OBJECTIVE

To investigate the accuracy and inter-reader reliability of CT angiography in children with suspected renal artery stenosis.

MATERIALS AND METHODS

This is a retrospective study of patients suspected of having renal artery stenosis evaluated by both CT angiography and DSA between 2008 and 2019 at a tertiary pediatric hospital. Only children who underwent CT angiography within 6 months before DSA were included. CT angiography studies were individually reviewed by two pediatric radiologists, blinded to clinical data, other studies and each other's evaluation, to determine the presence of stenosis at the main renal artery and 2nd- and 3rd-order branches. The sensitivity, specificity and accuracy were calculated using DSA as the reference. The effective radiation dose for CT angiography and DSA was also calculated. Kappa statistics were used to assess inter-reader agreement.

RESULTS

Seventy-four renal units were evaluated (18 girls, 19 boys). The patients' median age was 8 years (range: 1-21 years). Overall, CT angiography was effective in detecting renal artery stenosis with a sensitivity of 85.7%, specificity of 91.5% and accuracy of 88.9%. There was moderate inter-reader agreement at the main renal artery level (k=0.73) and almost perfect inter-reader agreement at the 2nd/3rd order (k=0.98). However, the sensitivity at the 2nd- and 3rd-order level was lower (14.3%). CT angiography provided excellent negative predictive value for evaluating renal artery stenosis at the main renal artery level (90.1%) and at the 2nd- or 3rd-order branches (82.7%). The median effective dose of CT angiography studies was 2.2 mSv (range: 0.6-6.3) while the effective dose of DSA was 13.7 mSv.

CONCLUSION

CT angiography has high sensitivity and specificity at the main renal artery level with a lower radiation dose than previously assumed. Therefore, it can be used as a diagnostic tool in patients with low to medium risk of renal artery stenosis, and as a screening and treatment planning tool in patients at high risk.

Visualization of the renal artery in kidney transplant patients using time-resolved computed tomography angiography

Background

Transplant renal artery stenosis (TRAS) is a post-operative complication which most often occurs between 3 months and 2 years after transplantation. TRAS is associated with kidney failure and hypertension and, thereby, with an increased risk of cardiovascular events.

Purpose

The purpose of this retrospective study was to report our experience of perfusion computed tomography angiography (P-CTA) to identify a 50% lumen reduction (as compared to digital subtraction angiography, DSA), assess its subjective image quality and evaluate if contrast-induced acute kidney injury (CI-AKI) occurred.

Material and Methods

All 13 patients who had undergone P-CTA for suspected TRAS at our institution were retrospectively evaluated. At P-CTA, eight or 12 g of iodine were administered intravenously, and five to seven scan sequences were merged into time-resolved images after motion correction. Eight patients underwent subsequent DSA.

Results

The average patient weight was 76 kg (range 55-97 kg). Image quality was rated as good or excellent for all patients, and pathological changes were shown in 10 of 13 patients undergoing P-CTA. Two patients had a serum creatinine increase of >26 μmol/L during the first 3 days, but serum creatinine was significantly lower in all patients 1 month after P-CTA (165+/-69 μmol/L versus 232+/-66 μmol/L, P < .01). The diagnosis at P-CTA was verified in all eight patients who underwent DSA. However, in two cases with suspected stenosis, renal function was restored without angioplasty.

Conclusion

Anatomy and blood flow of the transplant renal artery can be visualized using less than a third of the standard contrast media dose by using P-CTA technique.

The Renal Vasculature: What the Radiologist Needs to Know

The physiologic role of the kidneys is dependent on the normal structure and functioning of the renal vasculature. Knowledge and understanding of the embryologic basis of the renal vasculature are necessary for the radiologist. Common anatomic variants involving the renal artery (supernumerary arteries and prehilar branching) and renal vein (supernumerary veins, delayed venous confluence, retroaortic or circumaortic vein) may affect procedures like renal transplantation, percutaneous biopsy, and aortic aneurysm repair. Venous compression syndromes (anterior and posterior nutcracker syndrome) can be symptomatic and can be diagnosed with a combination of radiologic features. Renal artery stenosis is commonly atherosclerotic and is diagnosed with Doppler US, CT angiography, or MR angiography. Fibromuscular dysplasia, the second most common cause of renal artery narrowing, has a characteristic string-of-beads appearance resulting from multifocal stenoses and dilatations. Manifestations of renal vasculitis differ depending on whether the affected vessels are large, medium, or small. Renal vascular injury is graded according to the American Association for the Surgery of Trauma (AAST) renal injury scale, which defines vascular injury and active bleeding in renal injuries. Both renal arteries and veins are affected by primary neoplasms or secondarily by neoplasms from adjacent structures. Differentiation between bland thrombus and tumor thrombus and the extent of involvement dictate management in malignancies, especially renal cell carcinoma. Aneurysms, pseudoaneurysms, arteriovenous malformations, and arteriovenous fistulas can affect renal vessels and can be diagnosed with specific imaging features. The radiologist has a critical role in identification of specific imaging characteristics and establishing the diagnosis in the varied pathologic conditions affecting the renal vasculature, which is critical for directing management. Thus, the renal vasculature should be an integral part of radiologists' checklist. ^©RSNA, 2021.

K-edge Subtraction Computed Tomography with a Compact Synchrotron X-ray Source

In clinical diagnosis, X-ray computed tomography (CT) is one of the most important imaging techniques. Yet, this method lacks the ability to differentiate similarly absorbing substances like commonly used iodine contrast agent and calcium which is typically seen in calcifications, kidney stones and bones. K-edge subtraction (KES) imaging can help distinguish these materials by subtracting two CT scans recorded at different X-ray energies. So far, this method mostly relies on monochromatic X-rays produced at large synchrotron facilities. Here, we present the first proof-of-principle experiment of a filter-based KES CT method performed at a compact synchrotron X-ray source based on inverse-Compton scattering, the Munich Compact Light Source (MuCLS). It is shown that iodine contrast agent and calcium can be clearly separated to provide CT volumes only showing one of the two materials. These results demonstrate that KES CT at a compact synchrotron source can become an important tool in pre-clinical research.

An augmented patient-specific approach to administration of contrast agent for CT renal angiography

Purpose

This hybrid retrospective and prospective study performed on 200 consecutive patients undergoing renal CTA, investigates the opacification of renal vasculature, radiation dose, and reader confidence.

Materials and Methods

100 patients were assigned retrospectively to protocol A and the other 100 were allocated prospectively to protocol B. Both protocols implemented a contrast material and saline flow rate of 4.5 mL/sec. Protocol A utilized a 100 mL of low-osmolar nonionic IV contrast material (Ioversol 350 mg I/mL) while protocol B employed a patient-tailored contrast media formula using iso-osmolar non-ionic (Iodixanol 320 mg I/mL).

Results

Arterial opacification in the abdominal aorta and in the bilateral main proximal renal arteries demonstrated no statistical significance (p>0.05). Only the main distal renal artery of the left kidney in protocol B was statistically significant (p<0.046). In the venous circulation, the IVC demonstrated a significant reduction in opacification in protocol B (59.39 HU ± 19.39) compared to A (87.74 HU ± 34.06) (p<0.001). Mean CNR for protocol A (22.68 HU ± 13.72) was significantly higher than that of protocol B (14.75 HU ± 5.76 p< 0.0001). Effective dose was significantly reduced in protocol B (2.46 ± 0.74 mSv) compared to A (3.07 ± 0.68 mSv) (p<0.001). Mean contrast media volume was reduced in protocol B (44.56 ± 14.32 mL) with lower iodine concentration. ROC analysis demonstrated significantly higher area under the ROC curve for protocol B (p< 0.0001), with inter-reader agreement increasing from moderate to excellent in renal arterial visualization.

Conclusion

Employing a patient-tailored contrast media injection protocol shows a significant refinement in the visualization of renal vasculature and reader confidence during renal CTA.

Reduced Contrast Volume and Radiation Dose During Computed Tomography of the Pancreas: Timing-Specific Contrast Media Protocol

RATIONALE AND OBJECTIVE

To investigate the opacification of the pancreatic vasculature and parenchyma during computed tomography utilizing a patient-specific contrast formula.

MATERIALS AND METHODS

This hybrid prospective and retrospective study was approved by the institution review board. In 220 consecutive patients, pancreatic CT was performed with one of two protocols: protocol A, 100mL of contrast material injected via timed bolus triggering technique; or protocol B, employing a patient-specific contrast media protocol specifically timed at the gastroduodenal artery; both protocols employed 4.5 mL/s contrast media and 100mL saline chaser. Attenuation of pancreatic parenchymal, arterial, and venous vasculature supplying the pancreas was measured. Effective dose was calculated. Data were compared to the independent two-sample t test. Receiver operating characteristic, visual grading characteristic, and Cohens' kappa analyses were performed.

RESULTS

Mean pancreatic density measurements in each of the pancreatic segments during the arterial and venous phase were significantly higher in Protocol B (mean ± standard deviation, art: 96.59 HU ± 27.37; venous: 91.28 HU ± 20.88) compared to A (art: 77.86 HU ± 21.14; venous: 73.99 HU ± 14.75) (p < 0.0001). Mean arterial opacification was significantly higher in protocol B compared to A with the abdominal aorta (p < 0.007), superior mesenteric (p < 0.0002), gastroduodenal (proximal segment only p < 0.014), and splenic arteries (p < 0.036). In the venous circulation, the inferior vena cava, superior mesenteric, portal and splenic veins (all segments) demonstrated significant reduction in vascular opacification protocol B compared to A (p < 0.001). The contrast media volume in protocol B (57.60 ± 12.25 mL) was significantly lower than in protocol A (100 ± 1 mL) (p < 0.001). Effective dose was significantly reduced in protocol B (2.75 ± 0.63 mSv) compared to A (4.015 ± 0.89 mSv) (p < 0.001). Receiver operating characteristic and visual grading characteristic analysis demonstrated significantly higher area under the curve for protocol B (p < 0.0001) (p < 0.034) respectively, with inter-reader agreement increasing from good to excellent in pancreatic lesion detection.

CONCLUSION

Timing-specific contrast media protocol enhances image quality at reduced contrast volume and radiation dose during computed tomography of the pancreas.

Low-Tube-Voltage CT Urography Using Low-Concentration-Iodine Contrast Media and Iterative Reconstruction: A Multi-Institutional Randomized Controlled Trial for Comparison with Conventional CT Urography

OBJECTIVE

To compare the image quality of low-tube-voltage and low-iodine-concentration-contrast-medium (LVLC) computed tomography urography (CTU) with iterative reconstruction (IR) with that of conventional CTU.

MATERIALS AND METHODS

This prospective, multi-institutional, randomized controlled trial was performed at 16 hospitals using CT scanners from various vendors. Patients were randomly assigned to the following groups: 1) the LVLC-CTU (80 kVp and 240 mgI/mL) with IR group and 2) the conventional CTU (120 kVp and 350 mgI/mL) with filtered-back projection group. The overall diagnostic acceptability, sharpness, and noise were assessed. Additionally, the mean attenuation, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and figure of merit (FOM) in the urinary tract were evaluated.

RESULTS

The study included 299 patients (LVLC-CTU group: 150 patients; conventional CTU group: 149 patients). The LVLC-CTU group had a significantly lower effective radiation dose (5.73 ± 4.04 vs. 8.43 ± 4.38 mSv) compared to the conventional CTU group. LVLC-CTU showed at least standard diagnostic acceptability (score ≥ 3), but it was non-inferior when compared to conventional CTU. The mean attenuation value, mean SNR, CNR, and FOM in all pre-defined segments of the urinary tract were significantly higher in the LVLC-CTU group than in the conventional CTU group.

CONCLUSION

The diagnostic acceptability and quantitative image quality of LVLC-CTU with IR are not inferior to those of conventional CTU. Additionally, LVLC-CTU with IR is beneficial because both radiation exposure and total iodine load are reduced.

Split-bolus contrast injection protocol enhances the visualization of the thoracic vasculature and reduced radiation dose during chest CT

OBJECTIVE

To investigate the visualization of mediastinal lymph nodes during thoracic CT employing a multiphasic contrast media (CM) protocol.

METHODS

Institutional review board approved retrospective study consisting of 300 patients with known chest malignancy. Patients were allocated to one of two CM protocols: Protocol A, consisted of dual bolus (Phase 1:100 ml CM followed by 100 ml saline chaser) i.v. injected at 2.5 ml s^-1; Protocol B employed 100 ml of CM using a multiphasic injection protocol (Phase 1 and 2:60 ml contrast and saline, followed by Phase 3 and 4:40 ml contrast and saline injected at 2.5 ml s^-1) with a fixed scan delay of 70 s for each acquisition. Attenuation profiles of the thoracic arteries and veins were calculated as well as the arterio-venous contrast ratios (AVCR). Receiver operating characteristic (ROC), visual grading characteristic (VGC), and Cohen's kappa analysis were assessed.

RESULTS

Arterial opacification was up to 24% (p < 0.032) higher in protocol B than A, whereas, in the veins it was significantly lower in protocol B than A, with a maximum reduction of up to 84% (p < 0.0001). There was no statistical significance between the central and peripheral pulmonary arteries [>263 Hounsfield units (HU)] in each protocol. Protocol B, demonstrated significant improvement in AVCR at various anatomical sites (p < 0.002). Radiation dose was significantly reduced in protocol B compared to A (p < 0.004). Both ROC and VGC demonstrated significantly higher Az score for protocol B compared to A (p < 0.0001) with an increased inter reader agreement from poor to excellent.

CONCLUSION

Employing a multiphasic CM protocol significantly improves opacification of the thoracic vasculature and visualization of mediastinal lymph nodes during thoracic CT.

ADVANCES IN KNOWLEDGE

Uniform opacification between thoracic arteries and veins increases the delineation between vasculature and lymph nodes, reduces radiation dose when employing a multiphase contrast media injection protocol.

Low radiation dose in computed tomography: the role of iodine

Recent approaches to reducing radiation exposure during CT examinations typically utilize automated dose modulation strategies on the basis of lower tube voltage combined with iterative reconstruction and other dose-saving techniques. Less clearly appreciated is the potentially substantial role that iodinated contrast media (CM) can play in low-radiation-dose CT examinations. Herein we discuss the role of iodinated CM in low-radiation-dose examinations and describe approaches for the optimization of CM administration protocols to further reduce radiation dose and/or CM dose while maintaining image quality for accurate diagnosis. Similar to the higher iodine attenuation obtained at low-tube-voltage settings, high-iodine-signal protocols may permit radiation dose reduction by permitting a lowering of mAs while maintaining the signal-to-noise ratio. This is particularly feasible in first pass examinations where high iodine signal can be achieved by injecting iodine more rapidly. The combination of low kV and IR can also be used to reduce the iodine dose. Here, in optimum contrast injection protocols, the volume of CM administered rather than the iodine concentration should be reduced, since with high-iodine-concentration CM further reductions of iodine dose are achievable for modern first pass examinations. Moreover, higher concentrations of CM more readily allow reductions of both flow rate and volume, thereby improving the tolerability of contrast administration.

Renal Artery Stenosis: When to Revascularize in 2017

Atherosclerotic renal artery stenosis is the leading cause of secondary hypertension; it can also cause progressive renal insufficiency and cardiovascular complications such as refractory heart failure and flash pulmonary edema. Medical therapy including risk factor modification, renin-angiotensin-aldosterone system antagonists, lipid lowering agents, and antiplatelet therapy is the first line of treatment in all patients. Patients with uncontrolled renovascular hypertension despite optimal medical therapy, ischemic nephropathy, and cardiac destabilization syndromes who have severe renal artery stenosis are likely to benefit from renal artery revascularization. Screening for renal artery stenosis can be done with Doppler ultrasonography, computed tomographic angiography and magnetic resonance angiography. Invasive physiologic measurements are useful to confirm the severity of renal hypoperfusion and therefore improve the selection patients likely to respond to renal artery revascularization. Primary patency exceeds 80% at 5 years and surveillance for in-stent restenosis can be done with periodic clinical, laboratory, and imaging follow-up.

Prospective Comparison of Reduced-Iodine-Dose Virtual Monochromatic Imaging Dataset From Dual-Energy CT Angiography With Standard-Iodine-Dose Single-Energy CT Angiography for Abdominal Aortic Aneurysm

OBJECTIVE

The purpose of this study was to compare the image quality of reduced-iodine-dose single-source dual-energy CT angiography (CTA) with that of standard-iodine-dose single-energy CTA in examinations of patients with abdominal aortic aneurysm and to assess the effect of the concentration of iodinated contrast medium on intravascular enhancement and image quality of reduced-iodine-dose CTA.

SUBJECTS AND METHODS

In a prospective randomized clinical trial, 66 consecutively registered patients with abdominal aortic aneurysm who had previously undergone single-energy CTA (30-37 g I) underwent follow-up CTA at a reduced dose (21-27 g I) of iodinated contrast medium of either 270 mg I/mL (n = 33) or 320 mg I/mL (n = 33). Two readers independently evaluated virtual monochromatic imaging datasets (40-140 keV) and single-energy CTA images for image quality and noise and their preference for optimal energy virtual monochromatic imaging dataset. A value of p < 0.05 was considered statistically significant.

RESULTS

All 66 dual-energy CTA examinations were rated diagnostic with mean image quality and image noise scores of 4.8 and 4.5 for reader 1 and 3.8 and 3.4 for reader 2 compared with single-energy CTA results of 4.5 and 4.2 for reader 1 and 4.5 and 4.1 for reader 2. Low-energy virtual monochromatic images (40-60 keV) from reduced-iodine-dose (28%) dual-energy CTA had significantly higher intravascular aortic attenuation (26-185%) and contrast-to-noise ratio (CNR) (20-25%) than standard-iodine-dose single-energy CTA images (p < 0.0001). No significant difference was found between patients who received 270 and those who received 320 mg I/mL with respect to intravascular aortic attenuation (p = 0.6331) or CNR (p = 0.9775).

CONCLUSION

Low-energy virtual monochromatic imaging datasets from reduced-iodine (24 g I) single-source dual-energy CTA of the abdomen provide up to 185% higher attenuation and 25% higher CNR than standard-iodine-dose (33.3 g I) single-energy CTA while offering a wide range of energy settings irrespective of the concentration of IV contrast medium used.

Did low tube voltage CT combined with low contrast media burden protocols accomplish the goal of "double low" for patients? An overview of applications in vessels and abdominal parenchymal organs over the past 5 years

BACKGROUND

Imaging communities have already reached a consensus that the radiation dose of computed tomography (CT) should be reduced as much as reasonably achievable to lower population risks. Increasing attention is being paid to iodinated contrast media (CM) induced nephrotoxicity (CIN); a decrease in the intake of iodinated CM is required by increasingly more radiologists. Theoretically, the radiation dose varies with the tube current time and square of the tube voltage, with higher iodine contrast at low photon energies (Huda et al. [2000] Radiology, 21 7, 430-435).The use of low tube voltage is a promising strategy to reduce both the radiation dose and CM burden. The term 'double low' has been coined to describe scanning protocols that reduce radiation dose and iodine intake synchronously. These protocols are becoming increasingly popular in the clinical setting.

PURPOSE

The aim of this review was to describe all original studies using the 'double low' strategy in the last 5 years.

METHODS

We searched an online electronic database (PubMed) from January 2011 to December 2015 for original studies published on the relationship of low tube voltage with low radiation dose and low iodine contrast media burden in patients undergoing CT scans. Studies that failed to reduce radiation dose or iodine CM burden were excluded in this study.

RESULTS

Thirty-seven studies aimed at reducing radiation dose using low tube voltage combined with iodine CM reduced protocols were included in this study. Most studies evaluated conditions associated with arteries. Four were cerebral and neck computed tomography angiography (CTA) studies, 15 were pulmonary CTA (pCTA) and coronary CTA (cCTA) studies, one concerned myocardial perfusion, five studies focused on the thoracic and abdominal aorta, and one investigated renal arteries. Three studies consisted of CT venography (CTV) of the pelvis and lower extremities. Six publications examined the liver, and two focused on the kidney.

CONCLUSION

Overall, this review demonstrates that the low tube voltage CT protocol is a powerful tool to reduce the radiation dose in CTA, especially with pCTA and cCTA.

Double-low protocol for hepatic dynamic CT scan: Effect of low tube voltage and low-dose iodine contrast agent on image quality

The radiation-induced carcinogenesis from computed tomography (CT) and iodine contrast agent induced nephropathy has attracted international attention. The reduction of the radiation dose and iodine intake in CT scan is always a direction for researchers to strive. The purpose of this study was to evaluate the feasibility of a "double-low" (i.e., low tube voltage and low-dose iodine contrast agent) scanning protocol for dynamic hepatic CT with the adaptive statistical iterative reconstruction (ASIR) in patients with a body mass index (BMI) of 18.5 to 27.9 kg/m.A total of 128 consecutive patients with a BMI between 18.5 and 27.9 kg/m were randomly assigned into 3 groups according to tube voltage, iodine contrast agent, and reconstruction algorithms. Group A (the "double-low" protocol): 100 kVp tube voltage with 40% ASIR, iodixanol at 270 mg I/mL, group B: 120 kVp tube voltage with filtered back projection (FBP), iodixanol at 270 mg I/ mL, and group C: 120 kVp tube voltage with FBP, ioversol at 350 mg I/ mL.The volume CT dose index (CTDIvol) and effective dose (ED) in group A were lower than those in group B and C (all P < 0.01). The iodine intake in group A was decreased by approximately 26.5% than group C, whereas no statistical difference was observed between group A and B (P > 0.05). There was no significant difference of the CT values between group A and C (P > 0.05), which both showed higher CT values than that in group B (P < 0.001). However, no statistic difference was observed in the contrast-to-noise ratio (CNR), the signal-to-noise ratio (SNR), and image-quality scores among the 3 groups (all P > 0.05). Near-perfect consistency of the evaluation for group A, B, and C (Kenall's W = 0.921, 0.874, and 0.949, respectively) was obtained by the 4 readers with respect to the overall image quality.These results suggested that the "double-low" protocol with ASIR algorithm for multi-phase hepatic CT scan can dramatically decrease radiation dose and iodine intake with adequate image quality in patients with BMI of 18.5 to 27.9 kg/m.

Contrast medium administration and image acquisition parameters in renal CT angiography: what radiologists need to know

Over the last decade, exponential advances in computed tomography (CT) technology have resulted in improved spatial and temporal resolution. Faster image acquisition enabled renal CT angiography to become a viable and effective noninvasive alternative in diagnosing renal vascular pathologies. However, with these advances, new challenges in contrast media administration have emerged. Poor synchronization between scanner and contrast media administration have reduced the consistency in image quality with poor spatial and contrast resolution. Comprehensive understanding of contrast media dynamics is essential in the design and implementation of contrast administration and image acquisition protocols. This review includes an overview of the parameters affecting renal artery opacification and current protocol strategies to achieve optimal image quality during renal CT angiography with iodinated contrast media, with current safety issues highlighted.

Low tube voltage computed tomography urography using low-concentration contrast media: Comparison of image quality in conventional computed tomography urography

PURPOSE

The aim of the present study was to investigate the feasibility and image quality of excretory CT urography performed using low iodine-concentration contrast media and low tube voltage.

MATERIALS AND METHODS

This prospective study enrolled 63 patients who undergoing CT urography. The subjects were randomized into two groups of an excretory phase CT urography protocol and received either 240 mg I/mL of contrast media and 80 kVp of tube voltage (low-concentration protocol, n=32) or 350 mg I/mL and 120 kVp (conventional protocol, n=31). Two readers qualitatively evaluated images for sharpness of the urinary tract, image noise, streak artifact and overall diagnostic acceptability. The mean attenuation, signal-to-noise ratio, contrast-to-noise ratio and figure of merit were measured in the urinary tract. The non-inferiority test assessed the diagnostic acceptability between the two protocol groups.

RESULTS

The low-concentration protocol showed a significantly lower effective radiation dose (3.44 vs. 5.70 mSv, P<.001). The diagnostic acceptability was significantly lower in the low-concentration protocol with iterative reconstruction algorithm than in the conventional protocol (4.06±0.45 vs. 4.50±0.37, P<.001), however, all subjects showed at least more than standard diagnostic acceptability and the difference resided in the predefined non-inferiority margin. The signal-to-noise ratio, contrast-to-noise ratio and figure of merit were significantly higher in the low-concentration protocol along the entire urinary tract (P<.001).

CONCLUSION

CT urography using 240 mg I/mL iodine contrast media, 80 kVp tube voltage and an iterative reconstruction algorithm is beneficial to reduce radiation dose and iodine load, and its objective image quality and subjective diagnostic acceptability is not inferior to that of conventional CT urography.

Role of low dose CT angiography in the follow-up after endovascular aneurysm repair of abdominal aorta

BACKGROUND

Computed tomography angiography (CTA) is the most employed modality in the follow-up after endovascular aneurysm repair (EVAR) of abdominal aorta (AA); repeated standard controls expose patients to a high cumulative radiation dose (RD).

PURPOSE

To compare image quality and RD between 100 kV and 120 kV protocols in the same group of patients, previously treated with EVAR.

MATERIAL AND METHODS

Thirty patients, who had performed a previous CTA at 120 kV, underwent a low dose CTA with the same 64-detector machine. Images were evaluated qualitatively and quantitatively. The influence of body mass index (BMI), considering three groups of patients (normal weight, overweight, and obese) was also assessed. RD values (volume CT dose index and effective dose) were calculated.

RESULTS

The mean qualitative score at 100 kV was worse than that at 120 kV, but the difference was not statistically significant and in all cases the image quality was satisfactory. At 100 kV the vessels mean attenuation value was significantly higher; signal-to-noise ratio significantly lower; contrast-to-noise ratio lower, but the difference was not significant. Regarding BMI, the difference in the qualitative score was significant in the obese group, but not in the other two groups; of the quantitative parameters only the signal-to-noise ratio presented a significant difference in the obese group. The average CTDIvol was reduced by 22% and the mean effective dose by 36% with the 100 kV protocol compared to the 120 kV protocol. Both differences were significant.

CONCLUSION

The 100 kV protocol allowed a consistent RD reduction, maintaining a satisfactory image quality in all patients.

CT angiography in potential living kidney donors: 80 kVp versus 120 kVp

OBJECTIVE

The purpose of this article is to retrospectively investigate the diagnostic accuracy, image quality, and radiation dose of renal artery CT angiography (CTA), at 80 kVp compared with 120 kVp, in adult kidney donors.

MATERIALS AND METHODS

CTA examinations of 258 consecutive potential kidney donors were retrospectively evaluated; 189 patients were scanned using 64-MDCT scanners (higher maximal tube current), and 69 patients were scanned using 16-MDCT scanners (lower maximal tube current). On the basis of the tube potential and scanners, the study population was divided into four groups. Qualitative and quantitative analysis include vascular attenuation measurements, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR). Volume CT dose index (CTDIvol) was recorded, and size-specific dose estimate was also estimated.

RESULTS

Using 80 kVp for the 16-MDCT scanner, there was a 64.9% reduction in size-specific dose estimate (66.1% reduction in CTDIvol), increased noise, and tube current saturation in all cases. Axial image quality was significantly lower compared with that obtained at 120 kVp (p = 0.02), but image quality and visibility of renal artery branch order were comparable. Using 80 kVp for the 64-MDCT scanner, there was a 40.5% reduction in size-specific dose estimate (43.6% reduction in CTDIvol) and increased SNR and CNR (p < 0.001). No significant differences in 3D image quality and branch order visibility were observed. Tube current saturation was reached in 31% of cases. One hundred fifty-one patients (86 imaged at 80 kVp and 65 imaged at 120 kVp) underwent donor nephrectomy; CTA diagnostic accuracy was 100%.

CONCLUSION

Renal artery CTA using 80 kVp combined with limiting the tube current results in a significant reduction in radiation dose and improved SNR and CNR, without deterioration of image quality.

Effects of different tube potentials and iodine concentrations on image enhancement, contrast-to-noise ratio and noise in micro-CT images: a phantom study

The study aimed to investigate the effects of different tube potentials and concentrations of iodinated contrast media (CM) on the image enhancement, contrast-to-noise ratio (CNR) and noise in micro-computed tomography (µCT) images. A phantom containing of five polyethylene tube was filled with 2 mL of deionized water and iodinated CM (Omnipaque 300 mgI/mL) at four different concentrations: 5, 10, 15, and 20 mol/L, respectively. The phantom was scanned with a µCT machine (SkyScan 1176) using various tube potentials: 40, 50, 60, 70, 80, and 90 kVp, a fixed tube current; 100 µA, and filtration of 0.2 mm aluminum (Al). The percentage difference of image enhancement, CNR and noise of all images, acquired at different kVps and concentrations, were calculated. The image enhancement, CNR and noise curves with respect to tube potential and concentration were plotted and analysed. The highest image enhancement was found at the lowest tube potential of 40 kVp. At this kVp setting, the percentage difference of image enhancement [Hounsfield Unit (HU) of 20 mol/L iodine concentration over HU of deionized water] was 43%. By increasing the tube potential, it resulted with the reduction of HU, where only 17.5% different were noticed for 90 kVp. Across all iodine concentrations (5-20 M), CNR peaked at 80 kVp and then these values showed a slight decreasing pattern, which might be due insufficient tube current compensation. The percentage difference of image noise obtained at 40 and 90 kVp was 72.4%. Lower tube potential setting results in higher image enhancement (HU) in conjunction with increasing concentration of iodinated CM. Overall, the tube potential increment will substantially improve CNR and reduce image noise.

Perihilar branching patterns of renal artery and extrarenal length of arterial branches and tumour-feeding arteries on multidetector CT angiography

OBJECTIVE

The purpose of our study was to assess the extrarenal length of renal arterial branches and tumour-feeding arteries on multidetector CT (MDCT) angiography, in addition to the perihilar branching patterns, with relevance to segmental artery clamping.

METHODS

MDCT angiograms of 64 patients with renal masses <4 cm were retrospectively reviewed by 2 radiologists. The perihilar branching patterns of the single main renal artery were assessed according to the number of pre-segmental and segmental arteries. The extrarenal lengths of segmental plus pre-segmental arteries and the tumour-feeding arteries, measured on volume-rendered images, were compared according to the vascular segmentation and the tumour location, respectively.

RESULTS

In the 116 kidneys, 1 pre-segmental plus 5 segmental arteries (n=48) was the most common branching pattern. The mean extrarenal length of the inferior segmental plus pre-segmental arteries (33.05 mm) and the posterior segmental plus pre-segmental arteries (32.30 mm) was longer than any of the other segmental plus pre-segmental arteries (apical, 23.87 mm; superior, 26.80 mm; middle, 29.23 mm) (p<0.05). The mean extrarenal length of the lower pole tumour-feeding arteries (35.94 mm) was longer than those of the upper and mid-pole tumour-feeding arteries (24.95 mm, 29.62 mm), with significant difference between the lower and the upper pole tumour-feeding arteries (p<0.05).

CONCLUSION

Tumours in the lower pole, supplied by the inferior or posterior segmental artery, may be more amenable to segmental artery clamping.

ADVANCES IN KNOWLEDGE

MDCT angiography with volume rendering can demonstrate the extrarenal length of tumour-feeding arteries and may help in determining the accessibility for segmental artery clamping.

The role of CT angiography in the evaluation of pediatric renovascular hypertension

Historically, the evaluation of renovascular hypertension has been accomplished by US, renal scintigraphy and digital subtraction angiography. Based on its high accuracy reported in adults renal CT angiography (CTA) with pediatric-appropriate low radiation dose techniques has become an important tool in the workup of renovascular hypertension in children. Renal CTA has several advantages over more conventional imaging modalities, including rapid and non-invasive acquisition, high resolution and easy reproducibility. Additionally, in our experience high-quality renal CTA can be performed using low-dose radiation exposures and can be acquired without sedation in most instances. This article illustrates by examples the usefulness of renal CTA for diagnosis of childhood renovascular hypertension and provides an overview of renal CTA findings in the most common childhood renovascular diseases.