Comparison of standard- and low-tube voltage MDCT angiography in patients with peripheral arterial disease

Image quality, contrast enhancement and radiation dose of electrocardiograph- versus non-electrocardiograph-triggered computed tomography angiography of the aorta

INTRODUCTION

Computed tomography angiography of the aorta (CTAA) is the modality of choice for investigating aortic disease. Our aim was to evaluate the image quality, contrast enhancement and radiation dose of electrocardiograph (ECG)-triggered and non-ECG-triggered CTAA on a 256-slice single-source CT scanner. This allows the requesting clinician and the radiologist to balance radiation risk and image quality.

METHODS

We retrospectively assessed the data of 126 patients who had undergone CTAA on a single-source CT scanner using ECG-triggered (group 1, n = 77) or non-ECG-triggered (group 2, n = 49) protocols. Radiation doses were compared. Qualitative (4-point scale) and quantitative image quality assessments were performed.

RESULTS

The mean volume CT dose index, dose length product and effective dose in group 1 were 12.4 ± 1.9 mGy, 765.8 ± 112.4 mGy cm and 13.0 ± 1.9 mSv, respectively. These were significantly higher compared to group 2 values (9.1 ± 2.6 mGy, 624.1 ± 174.8 mGy cm and 10.6 ± 3.0 mSv, respectively) ( P < 0.001). Qualitative assessment showed the image quality at the aortic root-proximal ascending aorta was significantly higher in group 1 (median 3) than in group 2 (median 2, P < 0.001). Quantitative assessment showed significantly better mean arterial attenuation, signal-to-noise ratio and contrast-to-noise ratio in ECG-triggered CTAA compared to non-ECG-triggered CTAA.

CONCLUSION

ECG-triggered CTAA in a single-source scanner has superior image quality and vessel attenuation of aortic root/ascending aorta, but a higher radiation dose of approximately 23%. Its use should be considered specifically when assessing aortic root/ascending aorta pathology.

[A Review of Current Knowledge for X-ray Energy in CT: Practical Guide for CT Technologist]

In computed tomography (CT) systems, the optimal X-ray energy in imaging depends on the material composition and the subject size. Among the parameters related to the X-ray energy, we can arbitrarily change only the tube voltage. For years, the tube voltage has often been set at 120 kVp. However, since about 2000, there has been an increasing interest in reducing radiation dose, and it has led to the publication of various reports on low tube voltage. Furthermore, with the spread of dual-energy CT, virtual monochromatic X-ray images are widely used since the contrast can be adjusted by selecting the optional energy. Therefore, because of the renewed interest in X-ray energy in CT imaging, the issue of energy and imaging needs to be summarized. In this article, we describe the basics of physical characteristics of X-ray attenuation with materials and its influence on the process of CT imaging. Moreover, the relationship between X-ray energy and CT imaging is discussed for clinical applications.

Image quality in abdominal CT using an iodine contrast reduction algorithm employing patient size and weight and low kV CT technique

BACKGROUND

Low tube potential-high tube current computed tomography (CT) imaging allows reduction in iodine-based contrast dose and may extend the benefit of routine contrast-enhanced CT exams to patients at risk of nephrotoxicity.

PURPOSE

To determine the ability of an iodine contrast reduction algorithm to maintain diagnostic image quality for contrast-enhanced abdominal CT.

MATERIAL AND METHODS

CT exams with iodine contrast reduction were prescribed for patients at risk for renal dysfunction. The iodine contrast reduction algorithm combines weight-based contrast volume reduction with patient width-based low tube potential selection and bolus-tracking. Control exams with routine iodine dose were selected based on weight, width, and scan protocol. Three radiologists evaluated image quality and diagnostic confidence using a 4-point scale (<2 acceptable). Another radiologist assessed contrast reduction indications and measured portal vein and liver contrast-to-noise ratios.

RESULTS

Forty-six contrast reduction algorithm and control exams were compared (mean creatinine 1.6 vs. 1.2 mg/dL, P ≤ 0.0001). Thirty-nine contrast reduction patients had an eGFR <60 mL/min/1.73m² and 15 had single or transplanted kidney. Mean iodine contrast dose was lower in the contrast reduction group (20.9 vs. 39.4 g/mL, P < 0.0001). Diagnostic confidence was rated as acceptable in 95% (131/138) of contrast reduction and 100% of control exams (1.18-1.28 vs. 1.02-1.13, respectively; P > 0.06). Liver attenuation and contrast-to-noise ratio (CNR) were similar (P = 0.08), but portal vein attenuation and CNR were lower with contrast-reduction (mean 176 vs. 198 HU, P = 0.02; 13 vs. 16, P = 0.0002).

CONCLUSION

This size-based contrast reduction algorithm using low kV and bolus tracking reduced iodine contrast dose by 50%, while achieving acceptable image quality in 95% of exams.

Updates in Vascular Computed Tomography

Computed tomography angiography (CTA) has become a mainstay for the imaging of vascular diseases, because of high accuracy, availability, and rapid turnaround time. High-quality CTA images can now be routinely obtained with high isotropic spatial resolution and temporal resolution. Advances in CTA have focused on improving the image quality, increasing the acquisition speed, eliminating artifacts, and reducing the doses of radiation and iodinated contrast media. Dual-energy computed tomography provides material composition capabilities that can be used for characterizing lesions, optimizing contrast, decreasing artifact, and reducing radiation dose. Deep learning techniques can be used for classification, segmentation, quantification, and image enhancement.

COMPARISON OF RADIATION DOSE AND IMAGE QUALITY IN CTA OF THE PERIPHERAL ARTERIES

The aim of this study is to investigate the possibility of replacing the standard CTA protocol for peripheral arteries with a low dose CTA protocol without affecting the diagnostic image quality. Therefore a single centre retrospective study was conducted involving 200 exams of patients undergoing lower limb angiography. All exams were performed on a 64-row detector CT and the vascular density, muscle density, noise and radiation dose of each image were assessed. The subjective image quality was evaluated additionally by an experienced radiologist. Significant differences were observed in radiation dose and image quality between the standard CTA protocol and the lower dose CTA protocol. No differences were found between objective and subjective image quality. Using 80kVp instead of 120kVp as the tube voltage for lower limb CTA reduces the radiation dose without affecting the diagnostic image quality.

Basic Concepts of Contrast Injection Protocols for Coronary Computed Tomography Angiography

BACKGROUND

Coronary Computed Tomography Angiography (CTA) has become one of the most important diagnostic imaging modalities for the evaluation of coronary artery diseases. During coronary computed CTA, sufficient vascular enhancement is essential for the accurate detection and evaluation of lesions in the coronary arteries. To obtain optimal contrast enhancement and perform appropriate clinical coronary CTA, physicians, radiologists, and radiology technologists should acquire a basic knowledge of contrast injection protocols.

CONCLUSION

This review article summarizes the basic concepts of contrast injection protocols for coronary CTA.

CT Angiography in the Lower Extremity Peripheral Artery Disease Feasibility of an Ultra-Low Volume Contrast Media Protocol

Purpose

The ALARA principle is not only relevant for effective dose (ED) reduction, but also applicable for contrast media (CM) management. Therefore, the aim was to evaluate the feasibility of an ultra-low CM protocol in the assessment of peripheral artery disease (PAD).

Materials and methods

Fifty PAD patients were scanned on third-generation dual-source computed tomography, from diaphragm to the forefoot, as follows: tube voltage: 70 kV, reference effective tube current: 90 mAs, collimation: 192 × 2 × 0.6 mm, with individualized acquisition timing. The protocol ED (mSv) was quantified with dedicated software. CM protocol consisted of 15 ml test bolus and 30 ml main bolus (300 mgI/ml) injected at 5 ml/s, followed by a 40 ml saline chaser at the same flow rate. Aorto-popliteal bolus transit time was used to calculate the overall acquisition time and delay. Objective (hounsfield units—HU; contrast-to-noise ratio—CNR) and subjective image quality (four-point Likert score) were assessed at different anatomical regions from the aorta down to the forefoot.

Results

Mean attenuation values were exceeding 250 HU from aorta down to the anterior tibial artery with CNR < 13. However, decline in attenuation was observed in more distal region with mean values of 165 and 199 HU, in left and right dorsalis pedis artery, respectively. Mode subjective image quality from the level of aorta down to the popliteal segment was excellent; below the knee mode score was good. The mean ED per protocol was 1.1 ± 0.5 mSv.

Conclusion

Use of an ultra-low CM volume protocol at 70 kV is feasible in the evaluation of PAD, resulting in good to excellent image quality with mean ED of 1.1 ± 0.5 mSv.

Level of evidence

Level 3, Local non-random sample

Low-Tube Voltage Computed Tomography During Hepatic Arterial Phase: The Effect of Body Habitus on Image Quality

PURPOSE

This study aimed to evaluate the impact of body habitus factors on image quality of low-tube voltage computed tomography (CT) during the hepatic arterial phase.

MATERIALS AND METHODS

Ninety-seven patients (66 men, 31 women; age range, 26-78 years) who underwent clinically indicated liver dynamic CT examination were enrolled in the study. Analysis with 80-kVp CT and intermediate tube current (277-337 mA) was performed in the late hepatic arterial phase using a 320-detector row scanner with adaptive iterative dose reduction 3-dimensional reconstruction. Patient body habitus was measured using body weight (BW), body mass index (BMI), lateral width (LW) of the abdomen, and muscle volume (MV) of the abdominal wall. On hepatic arterial phase, the mean image noise and contrast-to-noise ratio (CNR) for the aorta and liver were assessed. The correlations between body habitus factors and image quality parameters were evaluated.

RESULTS

In all patients, MV showed the strongest correlation with image noise, followed by BW and LW (r = 0.684, 0.570, and 0.555, respectively). The BMI showed the fourth strongest correlation with image noise among all body habitus factors (r = 0.377). With respect to CNR of the aorta, MV and BW showed the strongest inverse correlation (r = -0.590 and -0.600, respectively), followed by LW and BMI (r = -0.557 and -0.423, respectively). Regarding the CNR of the liver, MV showed the strongest inverse correlation (r = -0.279), although the correlation efficiency was weak compared with other correlations.

CONCLUSIONS

Among various body habitus factors, MV showed the strongest association with image noise and CNR in the hepatic arterial phase using 80-kVp CT.

Indirect CT Venography at 80 kVp with Sinogram-Affirmed Iterative Reconstruction Compared to 120 kVp with Filtered Back Projection: Assessment of Image Quality and Radiation Dose

Objective

To evaluate the image quality and radiation dose of indirect computed tomographic venography (CTV) using 80 kVp with sinogram-affirmed iterative reconstruction (SAFIRE) and 120 kVp with filtered back projection (FBP).

Materials and Methods

This retrospective study was approved by our institution and informed consent was waived. Sixty-one consecutive patients (M: F = 27: 34, mean age 60 ± 16, mean BMI 23.6 ± 3.6 kg/m²) underwent pelvic and lower extremity CTVs [group A (n = 31, 120 kVp, reconstructed with FBP) vs. group B (n = 30, 80 kVp, reconstructed with SAFIRE)]. The vascular enhancement, image noise, contrast-to-noise ratio (CNR), and signal-to-noise ratio (SNR) were compared. Subjective image analysis for image quality and noise was performed by two radiologists. Radiation dose was compared between the two groups.

Results

Compared with group A, higher mean vascular enhancement was observed in the group B (group A vs. B, 118.8 ± 15.7 HU vs. 178.6 ± 39.6 HU, p < 0.001), as well as image noise (12.0 ± 3.8 HU vs. 17.9 ± 6.1 HU, p < 0.001) and CNR (5.1 ± 1.9 vs. 7.6 ± 3.0, p < 0.001). The SNRs were not significantly different in both groups (11.2 ± 4.8 vs. 10.8 ± 3.7, p = 0.617). There was no significant difference in subjective image quality between the two groups (all p > 0.05). The subjective image noise was higher in the group B (p = 0.036 in reader 1, p = 0.005 in reader 2). The inter-observer reliability for assessing subjective image quality was good (ICC 0.746~0.784, p < 0.001). The mean CT dose index volume (CTDIvol) and mean dose length product (DLP) were significantly lower in group B than group A [CTDIvol, 6.4 ± 1.3 vs. 2.2 ± 2.2 mGy (p < 0.001); DLP, 499.1 ± 116.0 vs. 133.1 ± 45.7 mGy × cm (p < 0.001)].

Conclusions

CTV using 80 kVp combined with SAFIRE provides lower radiation dose and improved CNR compared to CTV using 120 kVp with FBP.

Advances in axial imaging of peripheral vascular disease

Peripheral artery disease (PAD) has become increasingly common in the US patient population and can be a highly symptomatic and significant source of morbidity. When PAD is suspected, the first-line screening study that is obtained is typically a noninvasive evaluation that includes the ankle brachial index (ABI). Following a positive screening study, invasive catheter digital subtraction angiography (DSA) has been historically used to image the peripheral artery system and still remains the gold standard. However, newer developments in axial imaging including computed tomography angiography (CTA) and magnetic resonance angiography (MRA) have in large part supplanted DSA for imaging the peripheral artery system in clinical practice. Benefits of CTA include rapid noninvasive acquisition, wide availability, high spatial resolution, and the ability to generate isotropic datasets on 64-detector row and higher CT scanners, thereby allowing for multiplanar 3D reformatting. Drawbacks of CTA include the exposure to both iodinated contrast and ionizing radiation, although the radiation dose exposure is lower than for DSA, and newer techniques such as using low tube voltage and rapid acquisition times allow for lower contrast doses. The presence of vascular calcification also limits the evaluation of small distal arteries using CTA, although the development of dual-energy CT techniques has significantly addressed this issue. Benefits of MRA include the avoidance of exposure to ionizing radiation and high diagnostic accuracy, while drawbacks include limited availability and increased cost along with the risk of nephrogenic systemic fibrosis that is associated with gadolinium-based contrast agents, although the latter can be mitigated by using newer non-contrast MR angiography techniques. Future technical advances in CT and MR hardware and software and MR pulse sequences will likely lead to the broader applicability and increased accuracy of noninvasive axial imaging in the evaluation of patients with peripheral artery disease.

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.

Using 80 kVp on a 320-row scanner for hepatic multiphasic CT reduces the contrast dose by 50 % in patients at risk for contrast-induced nephropathy

OBJECTIVES

We evaluated the effects of a low contrast material (CM) dose protocol using 80-kVp on the image quality of hepatic multiphasic CT scans acquired on a 320-row CT scanner.

METHODS

We scanned 30 patients with renal insufficiency (eGFR < 45 mL/min/1.73 m²) using 80-kVp and a CM dose of 300mgI/kg. Another 30 patients without renal insufficiency (eGFR > 60 mL/min/1.73 m²) were scanned with the conventional 120-kVp protocol and the standard CM dose of 600mgI/kg. Quantitative image quality parameters, i.e. CT attenuation, image noise, and the contrast-to-noise ratio (CNR) were compared and the visual image quality was scored on a four-point scale. The volume CT dose index (CTDI_vol) and the size-specific dose estimate (SSDE) recorded with the 80- and the 120-kVp protocols were also compared.

RESULTS

Image noise and contrast enhancement were equivalent for the two protocols. There was no significant difference in the CNR of all anatomic sites and in the visual scores for overall image quality. The CTDI_vol and SSDE were approximately 25-30 % lower under the 80-kVp protocol.

CONCLUSION

Hepatic multiphase CT using 80-kVp on a 320-row CT scanner allowed for a decrease in the CM dose and a reduction in the radiation dose without image quality degradation in patients with renal insufficiency.

KEY POINTS

• The 80-kVp CT protocol enabled reduction of contrast dose by 50 % • The 80-kVp CT protocol reduced the radiation dose by 25-33 % • There was no degradation in the image quality of the 80-kVp protocol.

Lowering radiation dose during dedicated colorectal cancer MDCT: comparison of low tube voltage and sinogram-affirmed iterative reconstruction at 80 kVp versus blended dual-energy images in a population of patients with low body mass index

PURPOSE

To assess the diagnostic accuracy, cancer staging, image quality, and radiation dose of 80-kVp computed tomography (CT) images for patients with colorectal cancers (CRCs) using sinogram-affirmed iterative reconstruction (SAFIRE).

METHODS

Sixty-four consecutive patients (mean weight 62.5  ±  11.3 kg, mean BMI 24.1  ±  3.3 kg/m(2)) with known CRC underwent dual-energy CT. Data were reconstructed as a weighted average (WA) 120-kVp dataset. Both filtered back projection (FBP) and SAFIRE were applied to reconstruct the WA 120-Kvp (Protocol A, B) and 80-kVp (Protocol C, D) image sets. The image noise, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) of the cancers, the normal reference tissues, and the effective dose for each protocol were assessed. The cancer detection, staging, and image quality were evaluated. Analysis of variance was used for statistical analysis.

RESULTS

Compared with the FBP datasets at WA 120-kVp (Protocol A) and 80-kVp (Protocol C), the SAFIRE-reconstructed images (Protocols B, D) demonstrated significantly lower image noise (P  <  0.0083). Protocol D yielded significantly higher CNRs and SNRs for the CRCs and normal reference tissues than did Protocols A and C (P  <  0.0083). Protocol D also exhibited a significantly higher CNR for the CRC and some normal reference tissues than did Protocol B (P  <  0.0083). For hypovascular liver metastases (n  =  10), Protocol D yielded better SNRs and significantly higher CNRs than did Protocol A (P  <  0.0083). Overall, accuracy for tumor staging and liver metastasis was 95.3% (61/64) and 100%, respectively, in all of the 4 protocols. The mean effective dose decreased 41% from the WA 120-kVp to the 80-kVp protocols (6.23 vs. 3.68 mSv).

CONCLUSIONS

The 80-kVp technique with SAFIRE provided high SNR, high CNR, and good accuracy for staging in nonobese patients with CRC. Our study results should be extrapolated to patient populations with a high BMI with caution. Further studies of high BMI patients are therefore warranted.

80-kVp CT angiography for endovascular aneurysm repair follow-up with halved contrast medium dose and preserved diagnostic quality

BACKGROUND

Follow-up of endovascular aneurysm repair (EVAR) with life-long computed tomography angiography (CTA) surveillance exposes patients with impaired renal function to repeated risks of contrast medium-induced nephropathy (CIN).

PURPOSE

To retrospectively compare vascular attenuation, image noise, contrast-to-noise ratio (CNR), subjective image quality and effective radiation dose (mSv) for CTA with a 16-multirow detector CT (MDCT) equipment at 80 kVp after EVAR using a contrast medium (CM) dose that is half of that used at 120 kVp.

MATERIAL AND METHODS

Forty patients with estimated glomerular filtration rate (eGFR) <45 mL/min underwent 80-kVp CTA with 160 mg I/kg, and 40 patients with eGFR ≥45 mL/min 120-kVp CTA with 320 mg I/kg (maximum dose weight, 80 kg). Arterial phase analysis included vascular attenuation, image noise and CNR, and calculated effective dose. Subjective image quality was assessed on a 4-point scale by two blinded readers at three different levels as well as overall.

RESULTS

Median values in the 80/120 kVp cohorts were: age, 74-75 years; body weight, 77/80 kg; BMI 24/27 kg/m(2); CM dose, 13/25 gram-iodine; gram-iodine/GFR ratio, 0.35/0.38; mean aortic attenuation, 313/326 HU; image noise, 26/32 HU; CNR 10-11; subjective image quality score, 3.0-3.5 (Reader 1) and 3.0-3.3 (Reader 2); number of non-diagnostic examinations, 0/1; and effective dose, 4.5/5.1 mSv. There was no statistically significant difference in aortic CNR and effective dose between the 80 and 120 kVp cohorts.

CONCLUSION

80 kVp 16-MDCT with halved CM dose tailored to body weight for CTA follow-up of EVAR may provide satisfactory diagnostic results compared to common standards and be beneficial for patients at risk of CIN, though the present CT equipment may limit the use of the method to patients below 90 kg or with a BMI below 35 kg/m(2).

Low-Voltage, High-Pitch Computerized Tomography Angiography of the Infrarenal Aorta and Lower Extremity Vessels: Assessment of Radiation Dose, Image Quality With Hybrid Iterative Reconstruction, and Efficacy of Test Injection Using a Monitoring Scan at Knee Level

OBJECTIVES

Our aim was to assess image quality and radiation dose of low-voltage high-pitch computed tomography angiography of the infrarenal aorta and lower extremities and evaluate the efficacy of test injection technique using a monitoring scan at knee level.

METHODS

A total of 60 patients with suspected peripheral arterial disease were divided into 2 groups: group 1 (30 patients, 80 kVp, high pitch [3.2], and hybrid iterative reconstruction [sinogram-affirmed iterative reconstruction]) and group 2 (30 patients, 120 kVp, low pitch [1.0], and filtered back projection reconstruction). The test injection technique at knee level was used to determine the scan delay time in group 1. The image quality and radiation exposure were compared.

RESULTS

There were significant differences between the 2 groups in mean (SD) arterial attenuation (80 vs 120 kVp: 507.78 [103.01] vs 317.54 [62.03] Hounsfield units, P < 0.001), mean (SD) signal-to-noise ratio (51.04 [20.29] vs 34.66 [9.94], P < 0.001), and contrast-to-noise ratio (44.83 [17.93] vs 28.26 [9.60], P < 0.001). No difference in subjective image quality was found between the 2 groups (all P > 0.05). The imaging time was significantly shorter in group 1 (2.70 [0.11] vs 14.65 [0.90s], P < 0.001). The mean (SD) effective dose was significantly lower in the 80 kVp group (0.76 [0.06] vs 4.29 [0.63] mSv, P < 0.001).

CONCLUSIONS

The 80-kVp high-pitch computed tomography angiography of the lower limbs using sinogram-affirmed iterative reconstruction yields reduction of radiation exposure as well as obtains acceptable image quality if acquisition protocols are used in conjunction with the test injection technique using monitoring scan at knee level to determine the delay time.

[Study of CT Automatic Exposure Control System (CT-AEC) Optimization in CT Angiography of Lower Extremity Artery by Considering Contrast-to-Noise Ratio]

PURPOSE

To evaluate the image quality and effect of radiation dose reduction by setting for computed tomography automatic exposure control system (CT-AEC) in computed tomographic angiography (CTA) of lower extremity artery.

METHODS

Two methods of setting were compared for CT-AEC [conventional and contrast-to-noise ratio (CNR) methods]. Conventional method was set noise index (NI): 14and tube current threshold: 10-750 mA. CNR method was set NI: 18, minimum tube current: (X+Y)/2 mA (X, Y: maximum X (Y)-axis tube current value of leg in NI: 14), and maximum tube current: 750 mA. The image quality was evaluated by CNR, and radiation dose reduction was evaluated by dose-length-product (DLP).

RESULTS

In conventional method, mean CNRs for pelvis, femur, and leg were 19.9±4.8, 20.4±5.4, and 16.2±4.3, respectively. There was a significant difference between the CNRs of pelvis and leg (P<0.001), and between femur and leg (P<0.001). In CNR method, mean CNRs for pelvis, femur, and leg were 15.2±3.3, 15.3±3.2, and 15.3±3.1, respectively; no significant difference between pelvis, femur, and leg (P=0.973) in CNR method was observed. Mean DLPs were 1457±434 mGy⋅cm in conventional method, and 1049±434 mGy·cm in CNR method. There was a significant difference in the DLPs of conventional method and CNR method (P<0.001).

CONCLUSION

CNR method gave equal CNRs for pelvis, femur, and leg, and was beneficial for radiation dose reduction in CTA of lower extremity artery.

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.

Dual Energy CT Angiography of Peripheral Arterial Disease: Feasibility of Using Lower Contrast Medium Volume

OBJECTIVE

One of the main drawbacks associated with Dual Energy Computed Tomography Angiography (DECTA) is the risk of developing contrast medium-induced nephropathy (CIN). The aim of the present study was firstly, to design an optimal CT imaging protocol by determining the feasibility of using a reduced contrast medium volume in peripheral arterial DECTA, and secondly, to compare the results with those obtained from using routine contrast medium volume.

METHODS

Thirty four patients underwent DECTA for the diagnosis of peripheral arterial disease. They were randomly divided into two groups: Group 1 (routine contrast volume group) with n = 17, injection rate 4-5 ml/s, and 1.5 ml/kg of contrast medium, and Group 2 ((low contrast volume group), with n = 17, injection rate 4-5ml/s, and contrast medium volume 0.75 ml/kg. A fast kilovoltage-switching 64-slice CT scanner in the dual-energy mode was employed for the study. A total of 6 datasets of monochromatic images at 50, 55, 60, 65, 70 and 75 keV levels were reconstructed with adaptive statistical iterative reconstruction (ASIR) at 50%. A 4-point scale was the tool for qualitative analysis of results. The two groups were compared and assessed quantitatively for image quality on the basis of signal-to-noise ratio (SNR) and contrast-to-noise-ratio (CNR). Radiation and contrast medium doses were also compared.

RESULTS

The overall mean CT attenuation and mean noise for all lower extremity body parts was significantly lower for the low volume contrast group (p<0.001), and varied significantly between groups (p = 0.001), body parts (p<0.001) and keVs (p<0.001). The interaction between group body parts was significant with CT attenuation and CNR (p = 0.002 and 0.003 respectively), and marginally significant with SNR (p = 0.047), with minimal changes noticed between the two groups. Group 2 (low contrast volume group) displayed the lowest image noise between 65 and 70 keV, recorded the highest SNR and CNR at 65 keV, and produced significantly lower results with respect to contrast medium volume and duration of contrast injection (p<0.001). The effect of radiation dose was not statistically significant between the two groups.

CONCLUSIONS

DECTA images created at 65 keV and 50% ASIR with low contrast medium volume protocol, yielded results that were comparable to routine contrast medium volume, with acceptable diagnostic images produced during the evaluation of peripheral arteries.

Surveillance Imaging Following Endovascular Aneurysm Repair

There is a significant risk of complication following endovascular abdominal repair (EVAR), including endoleak, graft translocation, thrombosis, and infection. Surveillance imaging is important for detecting EVAR complication. Surveillance modalities include conventional X-ray, computed tomography, magnetic resonance imaging, ultrasound, and conventional angiography, with inherent advantages and drawbacks to each modality. The authors present common complications following EVAR, and recent advances in the key modalities for surveillance.

Low-volume contrast medium protocol for comprehensive cardiac and aortoiliac CT assessment in the context of transcatheter aortic valve replacement

RATIONALE AND OBJECTIVES

To investigate the diagnostic performance of a comprehensive computed tomography (CT) protocol for both cardiac and aortoiliac evaluation of patients considered for transcatheter aortic valve replacement (TAVR) using a single, low-volume contrast medium (CM) injection.

MATERIALS AND METHODS

Forty-four TAVR candidates were retrospectively analyzed. All underwent retrospectively electrocardiogram-gated cardiac CT followed by high-pitch CT angiography of the aortoiliac vasculature using one of two single injection protocols of 320 mgI/mL iodine CM: group A (n = 22), iodine delivery rate-based (1.28 gI/s), 60-mL CM volume, 4.0 mL/s flow rate; group B (n = 22), clinical routine protocol, 100-mL CM volume, 4.0 mL/s flow rate. Mean arterial attenuation, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) were calculated. Subjective image quality was assessed.

RESULTS

Aortic root and iliofemoral dimensions could be analyzed in all cases. Patient characteristics showed no significant differences. Mean attenuation at the levels of the aortic root (285.8 ± 83.0 HU vs 327.5 ± 70.8 HU, P = .080) and the iliofemoral access route (256.8 ± 88.5 HU vs 307.5 ± 93.2 HU, P = .071), as well as SNR and CNR were nonsignificantly lower in group A compared to group B. Subjective image quality was equivalent.

CONCLUSIONS

In multimorbid TAVR patients, the performance of a combined CT protocol using a single low-volume CM bolus is feasible with maintained image quality compared to a standard protocol.

Low contrast dose protocol involving a 100 kVp tube voltage for hypervascular hepatocellular carcinoma in patients with renal dysfunction

PURPOSE

To evaluate the feasibility of a 20 % reduced contrast dose hepatic arterial phase (HAP) CT for hypervascular hepatocellular carcinoma (HCC) with 100 kVp.

MATERIALS AND METHODS

The study included 97 patients with hypervascular HCC who underwent dynamic CT, including HAP scanning. The 54 patients had an estimated glomerular filtration rate (eGFR) of ≥60 were scanned with our conventional 120 kVp protocol. The other 43 patients (eGFR < 60) underwent scans using a tube voltage of 100 kVp and a 20 % reduced contrast dose. We compared the estimated effective dose, image noise, tumor-liver contrast (TLC), and contrast-to-noise ratio (CNR) in the hepatic arterial phase between the two groups using the Student's t test.

RESULTS

Estimated effective dose and image noise were not significantly different between these groups (p = 0.67 and p = 0.20, respectively). The TLC and CNR were significantly higher for the 100 kVp protocol than for the 120 kVp protocol (52.2 HU ± 17.4 vs 40.8 HU ± 18.6, p < 0.01 and 6.8 ± 2.6 vs 5.5 ± 2.4, p = 0.01, respectively).

CONCLUSION

For hepatic arterial phase CT of hypervascular HCC, 100 kVp scan allows a 20 % reduction in the contrast dose without reduction in image quality compared with a standard 120 kVp CT protocol.

Image quality and radiation dose of lower extremity CT angiography at 70 kVp on an integrated circuit detector dual-source computed tomography

BACKGROUND

Despite the well-established requirement for radiation dose reduction there are few studies examining the potential for lower extremity CT angiography (CTA) at 70 kVp.

PURPOSE

To compare the image quality and radiation dose of lower extremity CTA at 70 kVp using a dual-source CT system with an integrated circuit detector to similar studies at 120 kVp.

MATERIAL AND METHODS

A total of 62 patients underwent lower extremity CTA. Thirty-one patients were examined at 70 kVp using a second generation dual-source CT with an integrated circuit detector (70 kVp group) and 31 patients were evaluated at 120 kVp using a first generation dual-source CT (120 kVp group). The attenuation and image noise were measured and signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. Two radiologists assessed image quality. Radiation dose was compared.

RESULTS

The mean attenuation of the 70 kVp group was higher than the 120 kVp group (575 ± 149 Hounsfield units [HU] vs. 258 ± 38 HU, respectively, P < 0.001) as was SNR (44.0 ± 22.0 vs 32.7 ± 13.3, respectively, P = 0.017), CNR (39.7 ± 20.6 vs 26.6 ± 11.7, respectively, P = 0.003) and the mean image quality score (3.7 ± 0.1 vs. 3.2 ± 0.3, respectively, P < 0.001). The inter-observer agreement was good for the 70 kVp group and moderate for the 120 kVp group. The dose-length product was lower in the 70 kVp group (264.5 ± 63.1 mGy × cm vs. 412.4 ± 81.5 mGy × cm, P < 0.001).

CONCLUSION

Lower extremity CTA at 70 kVp allows for lower radiation dose with higher SNR, CNR, and image quality when compared with standard 120 kVp.

Contrast agent and radiation dose reduction in abdominal CT by a combination of low tube voltage and advanced image reconstruction algorithms

OBJECTIVES

To assess image quality in abdominal CT at low tube voltage combined with two types of iterative reconstruction (IR) at four reduced contrast agent dose levels.

METHODS

Minipigs were scanned with standard 320 mg I/mL contrast concentration at 120 kVp, and with reduced formulations of 120, 170, 220 and 270 mg I/mL at 80 kVp with IR. Image quality was assessed by CT value, dose normalized contrast and signal to noise ratio (CNRD and SNRD) in the arterial and venous phases. Qualitative analysis was included by expert reading.

RESULTS

Protocols with 170 mg I/mL or higher showed equal or superior CT values: aorta (278-468 HU versus 314 HU); portal vein (205-273 HU versus 208 HU); liver parenchyma (122-146 HU versus 115 HU). In the aorta, all 170 mg I/mL protocols or higher yielded equal or superior CNRD (15.0-28.0 versus 13.7). In liver parenchyma, all study protocols resulted in higher SNRDs. Radiation dose could be reduced from standard CTDIvol = 7.8 mGy (6.2 mSv) to 7.6 mGy (5.2 mSv) with 170 mg I/mL.

CONCLUSION

Combining 80 kVp with IR allows at least a 47 % contrast agent dose reduction and 16 % radiation dose reduction for images of comparable quality.

KEY POINTS

• There is a balance between image quality, contrast dose and radiation dose. • Iterative reconstruction has a major, positive impact on this balance. • Both contrast dose and radiation dose can be reduced in abdominal CT. • The trade-off can be quantitatively described by a 3D model. • Contrast and radiation dose can be tailored according to specific safety concerns.

Reduced radiation dose and improved image quality at cardiovascular CT angiography by automated attenuation-based tube voltage selection: intra-individual comparison

OBJECTIVES

To evaluate the effect of automated tube voltage selection on radiation dose and image quality at cardiovascular CT angiography (CTA).

METHODS

We retrospectively analysed paired studies in 72 patients (41 male, 60.5 ± 16.5 years), who had undergone CTA acquisitions of the heart or aorta both before and after the implementation of an automated x-ray tube voltage selection algorithm (ATVS). All other parameters were kept identical between the two acquisitions. Subjective image quality (IQ) was rated and objective IQ was measured by image noise, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and figure of merit (FOM). Image quality parameters and effective dose were compared between acquisitions.

RESULTS

Overall subjective image quality improved with the percentage of cases scored as adequate or higher increasing from 79 % to 92 % after implementation of ATVS (P = 0.03). SNR (14.1 ± 5.9, 15.7 ± 6.1, P = 0.009), CNR (11.6 ± 5.3, 13.2 ± 5.6, P = 0.011), and FOM (19.9 ± 23.3, 43.8 ± 51.1, P < 0.001) were significantly higher after implementation of ATVS. Mean image noise (24.1 ± 8.4 HU, 22.7 ± 7.1 HU, P = 0.048) and mean effective dose (10.6 ± 5.9 mSv, 8.8 ± 5.0 mSv, P = 0.003) were significantly lower after implementation of ATVS.

CONCLUSIONS

Automated tube voltage selection can operator-independently optimize cardiovascular CTA image acquisition parameters with improved image quality at reduced dose.

KEY POINTS

• Automatic tube voltage selection optimizes tube voltage for each individual patient. • In this population, overall radiation dose decreased while image quality improved. • This tool may become valuable for improving dose/quality ratio.

Image quality and radiation dose of lower extremity CT angiography using 70 kVp, high pitch acquisition and sinogram-affirmed iterative reconstruction

Objectives

The purpose of this study was to assess image quality and radiation dose of lower extremity CT angiography (CTA) with 70 kVp, high pitch acquisition and sinogram-affirmed iterative reconstruction (SAFIRE).

Methods

Lower extremity CTAs were performed on 44 patients: 22 patients were examined using protocol A (120 kVp, pitch of 0.85 and 120 ml of contrast agent on a first-generation dual-source CT) (120 kVp group) and 22 patients were evaluated with protocol B (70 kVp, pitch of 2.2 and 80 ml of contrast agent on a second-generation dual-source CT) (70 kVp group). Images from the 120 kVp group were reconstructed with filtered back projection (FBP) and images from the 70 kVp group with SAFIRE. The attenuation, image noise, signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. Two radiologists subjectively assessed image quality of lower extremity arteries, plantar arterial enhancement and venous contamination of all patients. Radiation dose was compared between the two groups.

Results

Higher mean intravascular attenuation was obtained in the 70 kVp group (70 vs. 120 kVp group, 555.4±83.4 HU vs. 300.9±81.4 HU, P<0.001), as well as image noise (20.0±2.8 HU vs. 17.5±3.2 HU, P = 0.010), SNR (32.0±7.0 vs. 19.1±6.9, P<0.001) and CNR (28.1±6.6 vs 15.9±6.3, P<0.001). No difference in subjective image quality and plantar arterial enhancement was found between 120 kVp group and 70 kVp group (all P>0.05). The venous contamination score was 1.5±0.8 for 120 kVp group while no venous contamination was found in 70 kVp group. The inter-observer agreement was moderate to good for both groups (0.515∼1, P<0.001). The effective dose was lower in 70 kVp group (0.3±0.1 mSv) than in 120 kVp group (1.6±0.7 mSv)(P<0.001).

Conclusions

Lower extremity CTA using 70 kVp, high pitch acquisition and SAFIRE, except increasing imaging noise, allows for lower radiation dose and contrast material volume without compromising image quality.

Effects of High-concentration contrast material and low-voltage CT on contrast for multiphasic CT of the upper abdomen: comparison using the simulation with virtual monochromatic imaging obtained by fast-switch kVp dual-energy CT

Objective

The purpose of this study was to compare the effects of high-concentration contrast material and low-voltage CT simulated by virtual monochromatic (VM) imaging on contrast enhancement at multiphasic CT of the upper abdomen.

Methods

This study included 72 patients who underwent CT during early arterial (EAP), late arterial and portal venous phases after 300-mgI/ml (Group A; 34 patients) or 350-mg/ml (Group B; 38 patients) contrast-material injection at the same volumetric rate (0.067 mL/sec/kg). VM images were generated at 50 and 65 keV. Contrast-to-noise ratios (CNRs) of aorta, portal vein, and liver parenchyma were calculated and statistically compared.

Results

Mean CNRs for 50-keV VM images were significantly higher than 65-keV VM images of each organ at any phases (p < 0.05), except for hepatic parenchyma in EAP. Aortic CNRs in EAP on 65- and 50-keV images of Group B were significantly higher than Group A (p <0.05, respectively). Aortic CNR on 50-keV images of Group A and on 65-keV images of Group B were 11% and 21% higher than 65-keV images of Group A, respectively.

Conclusions

Low-voltage CT simulated by VM image improved contrast enhancement through any phases, while high-concentration contrast material increased only arterial contrast in EAP more effectively.

Diagnostic efficiency of low-dose CT angiography compared with conventional angiography in peripheral arterial occlusions

OBJECTIVE

The purpose of this study was to assess the diagnostic efficiency and radiation dose of peripheral arterial CT angiography (CTA) performed at a low tube voltage of 70 kV in comparison with conventional angiography.

SUBJECTS AND METHODS

Thirty consecutive patients (body mass index ≤ 25 kg/m(2)) with known or suspected peripheral arterial occlusion diseases underwent both CTA at a low tube voltage of 70 kV and conventional angiography. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy of peripheral arterial CTA were evaluated. The radiation dose was recorded.

RESULTS

Diagnostic CTA images were obtained in all patients. CTA allowed accurate identification, characterization, and measurement of all peripheral arterial occlusive diseases. In conventional angiography, 360 diseased segments were found among the 810 segments evaluated. The sensitivity, specificity, PPV, NPV, and accuracy of CTA were 100% (95% CI, 98.81-100%), 93.5% (90.96-95.36%), 90.86% (87.38-93.45%), 100% (99.17-100%), and 96.05% (94.48-97.19%), respectively, with a kappa value of 0.92 (excellent agreement). The mean CT dose index was 3.71 ± 0.8 mGy, and the dose-length product was 446.6 ± 35.7 mGy × cm. The effective dose was 1.94 ± 0.21 mSv for CTA and 4.41 ± 0.64 mSv for conventional angiography.

CONCLUSION

CTA of peripheral arteries with a low tube voltage of 70 kV provides reliable information and serves as a rapidly performed and easily available "one-stop-shop" imaging modality in the diagnosis of peripheral arterial occlusion diseases.

Low contrast volume run-off CT angiography with optimized scan time based on double-level test bolus technique--feasibility study

PURPOSE

To verify the technical feasibility of low contrast volume (40 mL) run-off CT angiography (run-off CTA) with the individual scan time optimization based on double-level test bolus technique.

MATERIALS AND METHODS

A prospective study of 92 consecutive patients who underwent run-off CTA performed with 40 mL of contrast medium (injection rate of 6 mL/s) and optimized scan times on a second generation of dual-source CT. Individual optimized scan times were calculated from aortopopliteal transit times obtained on the basis of double-level test bolus technique--the single injection of 10 mL test bolus and dynamic acquisitions in two levels (abdominal aorta and popliteal arteries). Intraluminal attenuation (HU) was measured in 6 levels (aorta, iliac, femoral and popliteal arteries, middle and distal lower-legs) and subjective quality (3-point score) was assessed. Relations of image quality, test bolus parameters and arterial circulation involvement were analyzed.

RESULTS

High mean attenuation (HU) values (468; 437; 442; 440; 342; 274) and quality score in all monitored levels was achieved. In 91 patients (0.99) the sufficient diagnostic quality (score 1-2) in aorta, iliac and femoral arteries was determined. A total of 6 patients (0.07) were not evaluable in distal lower-legs. Only the weak indirect correlation of image quality and test-bolus parameters was proved in iliac, femoral and popliteal levels (r values: -0.263, -0.298 and -0.254). The statistically significant difference of the test-bolus parameters and image quality was proved in patients with occlusive and aneurysmal disease.

CONCLUSION

We proved the technical feasibility and sufficient quality of run-off CTA with low volume of contrast medium and optimized scan time according to aortopopliteal transit time calculated from double-level test bolus.

CT angiography of the head-and-neck vessels acquired with low tube voltage, low iodine, and iterative image reconstruction: clinical evaluation of radiation dose and image quality

Objectives

We aimed to assess the effectiveness and feasibility of head-and-neck Computed Tomography Angiography (CTA) with low tube voltage and low concentration contrast media combined with iterative reconstruction algorithm.

Methods

92 patients were randomly divided into group A and B: patients in group A received a conventional scan with 120 kVp and contrast media of 320 mgI/ml. Patients in group B, 80 kVp and contrast media of 270 mgI/ml were used along with iterative reconstruction algorithm techniques. Image quality, radiation dose and the effectively consumed iodine amount between two groups were analyzed and compared.

Results

Image quality of CTA of head-and-neck vessels obtained from patients in group B was significantly improved quantitatively and qualitatively. In addition, CT attenuation values in group B were also significantly higher than that in group A (p<0.001). Furthermore, compared with the protocol whereby 120 kVp and 320 mgI/dl were administrated, the mean radiation dose and consumed iodine amount in protocol B were also reduced by 50% and 15.6%, respectively (p<0.001).

Conclusions

With the help of iterative reconstruction algorithm techniques, the head-and-neck CTA with diagnostic quality can be adequately acquired with low tube voltage and low concentration contrast media. This method could be potentially extended to include any part of the body to reduce the risks related to ionizing radiation.

Radiation dose and image quality at high-pitch CT angiography of the aorta: intraindividual and interindividual comparisons with conventional CT angiography

OBJECTIVE

The objective of our study was to evaluate radiation dose and quantitative image quality parameters at high-pitch CT angiography (CTA) of the aorta compared with conventional CTA.

MATERIALS AND METHODS

We studied the examinations of 110 patients (65 men and 45 women; mean age ± SD, 64 ± 15 years) who had undergone CTA of the entire aorta on a second-generation dual-source CT system; 50 examinations were performed in high-pitch mode. The mean arterial attenuation, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and figure of merit (FOM) were calculated for the high-pitch CTA and conventional CTA groups. Radiation exposures were compared.

RESULTS

All studies were considered of diagnostic quality. At high-pitch CTA, the mean tube voltage and tube current-exposure time product were 118 ± 7 kV (SD) and 197 ± 78 mAs compared with 120 ± 1 kV and 258 ± 78 mAs, respectively, at conventional CTA (p < 0.05). The mean volume CT dose index, dose-length product, and effective dose were 8.1 ± 2.4 mGy, 561.1 ± 178.6 mGy × cm, and 9.6 ± 3.0 mSv at high-pitch CTA and 18.3 ± 7.7 mGy, 1162.6 ± 480.1 mGy × cm, and 19.8 ± 8.2 mSv at conventional CTA (p < 0.001). Attenuation was similar for both protocols, whereas significantly less contrast medium was injected for high-pitch CTA than for standard-pitch CTA (87.3 ± 16 mL vs 97.9 ± 16 mL, respectively; p < 0.01). The SNR and CNR were significantly lower in the high-pitch CTA examinations (p < 0.01), whereas the FOM was nonsignificantly higher. Twenty patients underwent both high-pitch CTA and conventional CTA, with a 45% reduction in radiation dose (p < 0.001).

CONCLUSION

High-pitch CTA of the aorta yields 45-50% reduction of radiation exposure as well as contrast medium savings with maintained vessel attenuation.

Diagnostic accuracy of dynamic computed tomographic angiographic of the lower leg in patients with critical limb ischemia

OBJECTIVE

The purpose of this study was to assess the diagnostic accuracy of dynamic computed tomographic angiography (dyn-CTA) in patients with critical lower leg ischemia.

MATERIALS AND METHODS

A population of 29 patients with known peripheral arterial occlusive disease (Fontaine stage III or IV) was examined with a combined CTA protocol consisting of a standard CTA (s-CTA) of the lower leg runoff from the diaphragm to the toes and dyn-CTA of the calves (scan range, 48 cm; 8 phases; 3.5 seconds per phase, 100 kV; 120 mAs; contrast volume, 50 mL; flow rate, 5.0 mL/s). Digital subtraction angiography was performed on all patients and served as a reference standard. For each of seven lower leg artery segments, arterial contrast and diagnostic confidence for stenosis assessment (3-point scale) were tested for s-CTA and dyn-CTA. Similarly, stenoses of calf-segments were classified on a 3-point scale separately for s-CTA and dyn-CTA and were compared with digital subtraction angiography to assess diagnostic accuracy.

RESULTS

Compared with s-CTA, dyn-CTA resulted in significantly higher arterial contrast enhancement (68% vs 46% optimal contrast; P < 0.01) and higher diagnostic confidence (64% vs 48% fully confident, respectively, P < 0.05). Dyn-CTA had a slightly higher sensitivity for the detection of significant stenosis (98.0% vs 96.6%), and for the detection of occlusion (95.4% vs 94.4%). Specificity for dyn-CTA was higher than for s-CTA, both for detection of stenosis (97.1% vs 92.2%) and especially for the detection of vessel occlusions (99.3% vs 94.4%; P < 0.05).

CONCLUSIONS

Compared with s-CTA, dyn-CTA provides improved arterial contrast enhancement, higher diagnostic confidence, and increased diagnostic accuracy for the detection of stenoses and occlusions in peripheral arterial occlusive disease patients.

Low contrast agent and radiation dose protocol for hepatic dynamic CT of thin adults at 256-detector row CT: effect of low tube voltage and hybrid iterative reconstruction algorithm on image quality

PURPOSE

To evaluate the effect on image quality of a low contrast agent dose and radiation dose protocol at abdominal dynamic computed tomography (CT) with a low tube voltage, hybrid iterative reconstruction algorithm, and a 256- detector row scanner.

MATERIALS AND METHODS

This prospective study received institutional review board approval, and prior informed written consent was obtained from all patients. Seventy-four patients undergoing hepatic dynamic CT were randomly assigned to one of two protocols: Thirty-nine patients underwent scanning with the conventional 120-kVp protocol and the other 35 patients underwent scanning with an 80-kVp tube voltage and a 40% reduction in contrast agent dose. The 80-kVp images were also postprocessed with a hybrid iterative reconstruction algorithm. The estimated effective radiation dose of each protocol was compared and the image noise and contrast-to-noise-ratio (CNR) of the 120-kVp, 80-kVp, and hybrid iterative reconstructed 80-kVp images were evaluated by using the Student t test.

RESULTS

The effective radiation dose was 51% lower during the hepatic arterial phase (HAP) and 48% lower during the portal venous phase (PVP) with the 80-kVp protocol than with the 120-kVp protocol (HAP: 5.6 mSv ± 1.0 [standard deviation] vs 11.6 mSv ± 3.3; PVP: 5.8 mSv ± 0.7 vs 11.2 mSv ± 3.2, respectively). The hybrid iterative reconstruction decreased image noise by 23% during the HAP (9.2 ± 1.9 vs 12.0 ± 2.6) and by 24% during the PVP (9.4 ± 1.8 vs 12.3 ± 2.6). There were no significant differences in the CNR of any of the regions of interest between 80-kVp with iterative reconstruction and 120-kVp protocols (P = .46-.85).

CONCLUSION

A low tube voltage and the hybrid iterative reconstruction algorithm can dramatically decrease radiation and contrast agent doses with adequate image quality at hepatic dynamic CT of thin adults with use of a 256-detector row scanner.

Effect of hybrid iterative reconstruction technique on quantitative and qualitative image analysis at 256-slice prospective gating cardiac CT

OBJECTIVES

To evaluate the effect of hybrid iterative reconstruction on qualitative and quantitative parameters at 256-slice cardiac CT.

METHODS

Prospective cardiac CT images from 20 patients were analysed. Paired image sets were created using 3 reconstructions, i.e. filtered back projection (FBP) and moderate- and high-level iterative reconstructions. Quantitative parameters including CT-attenuation, noise, and contrast-to-noise ratio (CNR) were determined in both proximal- and distal coronary segments. Image quality was graded on a 4-point scale.

RESULTS

Coronary CT attenuation values were similar for FBP, moderate- and high-level iterative reconstruction at 293 ± 74-, 290 ± 75-, and 283 ± 78 Hounsfield units (HU), respectively. CNR was significantly higher with moderate- and high-level iterative reconstructions (10.9 ± 3.5 and 18.4 ± 6.2, respectively) than FBP (8.2 ± 2.5) as was the visual grading of proximal vessels. Visualisation of distal vessels was better with high-level iterative reconstruction than FBP. The mean number of assessable segments among 289 segments was 245, 260, and 267 for FBP, moderate- and high-level iterative reconstruction, respectively; the difference between FBP and high-level iterative reconstruction was significant. Interobserver agreement was significantly higher for moderate- and high-level iterative reconstruction than FBP.

CONCLUSIONS

Cardiac CT using hybrid iterative reconstruction yields higher CNR and better image quality than FBP.

KEY POINTS

• Cardiac CT helps clinicians to assess patients with coronary artery disease • Hybrid iterative reconstruction provides improved cardiac CT image quality • Hybrid iterative reconstruction improves the number of assessable coronary segments • Hybrid iterative reconstruction improves interobserver agreement on cardiac CT.

Combination of a low-tube-voltage technique with hybrid iterative reconstruction (iDose) algorithm at coronary computed tomographic angiography

We compare the performance of low tube voltage with the hybrid iterative reconstruction (iDose) with standard and low tube voltage with the filtered backprojection (FBP) using phantoms at computed tomographic coronary angiography. In computed tomographic coronary angiography, application of the combined low tube voltage with iDose resulted in significant image quality improvements compared to the low tube voltage with FBP. Image quality was the same or better despite a reduction in the radiation dose by 76% compared with standard tube voltage with FBP.

Abdominal dynamic CT in patients with renal dysfunction: contrast agent dose reduction with low tube voltage and high tube current-time product settings at 256-detector row CT

PURPOSE

To evaluate the feasibility of a low-contrast agent dose protocol at abdominal dynamic computed tomography (CT) with a low tube voltage high tube current-time product technique and a 256-detector row CT unit.

MATERIALS AND METHODS

This prospective study received institutional review board approval; written informed consent to participate was obtained from all patients. The study included 151 patients; 117 had an estimated glomerular filtration rate (eGFR) greater than or equal to 60 mL/min/1.73 m(2). These patients were examined with the conventional 120-kVp protocol. The other 34 patients underwent scanning with an 80-kVp tube voltage, a high tube current-time product, and a 40% reduction in contrast agent dose. Effective dose (ED), image noise, attenuation, contrast-to-noise ratio (CNR), and figure of merit of the aorta in the arterial phase and of the portal vein and hepatic parenchyma in the portal venous phase in the two groups were compared with the Student t test.

RESULTS

Estimated ED was about 20% lower with the 80-kVp protocol than with the 120-kVp protocol. There were no significant differences in CNR in any region of interest between the 80-kVp protocol and the 120-kVp protocol (abdominal aorta: 36.9 ± 9.7 [standard deviation] vs 36.1 ± 8.1, P = .63; portal vein: 13.4 ± 3.2 vs 13.1 ± 3.2, P = .65; hepatic parenchyma: 6.4 ± 2.6 vs 6.7 ± 2.3, P = .51).

CONCLUSION

Contrast dose at hepatic dynamic 256-detector row CT in patients with renal dysfunction can be decreased by 40% with this protocol by using the 80-kVp setting and a high tube current-time product.