Intravenous contrast material administration at high-pitch dual-source CT pulmonary angiography: test bolus versus bolus-tracking technique

Purpose

To compare test bolus and bolus tracking for the determination of scan delay of high-pitch dual-source CT pulmonary angiography in patients with suspected pulmonary embolism using 50 ml of contrast material.

Materials and methods

Data of 80 consecutive patients referred for CT pulmonary angiography were evaluated. All scans were performed on a 128-channel dual-source CT scanner with a high-pitch protocol (pitch 3.0, 100 kV, 180 mA s). Contrast enhancement was achieved by injecting 50 ml of iomeprol followed by a saline chaser of 50 ml injected at a rate of 4 ml/s. The scan delay was determined using either the test bolus (n = 40) or bolus tracking (n = 40) technique. Test bolus required another 15 ml CM to determine time to peak enhancement of the contrast bolus within the pulmonary trunk. Attenuation profiles in the pulmonary trunk and on segmental level as well as in the ascending aorta were measured to evaluate the timing techniques. Additionally, overall image quality was evaluated.

Results

In all patients an adequate and homogeneous contrast enhancement of more than 250 HU was achieved in the pulmonary arteries. No statistically significant difference between test bolus and bolus tracking was found regarding attenuation of the pulmonary arteries or overall image quality. However, using bolus tracking 15 ml CM less was injected.

Conclusion

A homogeneous opacification of the pulmonary arteries and sufficient image quality can be achieved with both the bolus tracking and test bolus techniques with significant lower contrast doses compared to conventional contrast material injection protocols.     

Dual-energy CT angiography of the lungs: Comparison of test bolus and bolus tracking techniques for the determination of scan delay

Objective

To prospectively compare test bolus and bolus tracking for the determination of scan delay of pulmonary dual-energy CT angiography in patients with suspected pulmonary embolism.

Materials and methods

60 consecutive patients referred for CTA for exclusion of PE were randomized either into a test bolus group or into a bolus tracking group. All exams were performed on a 64-channel dual source CT scanner. A standard single-acquisition dual-energy CTA was performed after injection of 100 ml Iomeprol 400 followed by a saline chaser of 4 ml/s. The scan delay was determined using either test bolus (n = 30) or bolus tracking (n = 30). Test bolus was performed using an additional 20 ml Iomeprol 400 injected with a rate of 4 ml/s during acquisition of a series of dynamic low-dose monitoring scans followed by injection of a saline bolus of 20 ml using the same flow rate. For DECT angiography of the lungs 100 ml Iomeprol 400 was injected with an injection rate of 4 ml/s followed by a saline chaser of 20 ml using the same flow rate. Attenuation profiles of different vascular segments (pulmonary arteries, pulmonary parenchyma, aorta, all 4 heart chambers) were measured to evaluate the timing techniques. Overall image quality of dual-energy “perfusion” maps and virtual 120 kV CTA images was evaluated by two radiologists regarding the present of artifacts.

Results

In all patients an adequate and homogeneous contrast enhancement of more than 400 Hounsfield units (HU) was achieved in the different vascular districts. No statistically significant difference between test bolus and bolus tracking was found regarding vessel attenuation or overall image quality.

Conclusion

A homogeneous opacification of the different vascular territories and the pulmonary parenchyma as well as a sufficient image quality can be achieved with either bolus tracking or test bolus techniques.     

Optimisation of contrast medium volume and injection-related factors in CT pulmonary angiography: 64-slice CT study

Objective

To compare the image quality of computed tomography pulmonary angiography (CTPA) obtained with the injection of various low doses of contrast medium (CM) with different injection-related factors.

Methods

A total of 90 patients (42 females, 48 males; 54.3?±?18.6 years) undergoing CTPA were included. Three CM protocols, each containing 30 patients, were created. Protocols 1, 2 and 3 consisted of a CM of 60 ml, 55 ml and 50 ml, and a bolus trigger level of 120 HU, 90 HU and 75 HU, respectively. Injection was uniphasic for protocols 1 and 2 (flow rate 5 ml/s), and biphasic for protocol 3 (flow rates 5 and 4 ml/s); with saline flushing afterwards. Enhancement was measured in three central and six peripheral pulmonary arteries.

Results

The mean attenuation value for pulmonary arteries was over 250 HU for all protocols. There was no difference between the attenuation levels with the protocols (p?>?0.05). The percentage of pulmonary arteries exceeding optimal attenuation (≥250 HU) showed that protocols 2 and 3 were 90–100% successful (p?<?0.05).

Conclusion

The use of proper injection-related factors during CTPA, such as a low trigger level and a high flow rate with saline injection following a decreased CM volume (55 ml or 50 ml), will enable adequate pulmonary artery contrast enhancement.     

Contrast-enhanced three-dimensional MR angiography of the thoracic aorta: experiences after 118 examinations with a standard dose contrast administration and different injection protocols

The aim of this study was to test three injection protocols for contrast-enhanced magnetic resonance angiography (MRA) of the thoracic aorta with a standard-dose application. Ninety-three patients with a total of 118 examinations underwent MRA of the thoracic aorta at 1.5 T. There were three injection protocols: in 24 cases, no test bolus was performed and contrast was injected manually; in 14 cases, contrast was injected manually after a test bolus; and in 80 cases, a MR-compatible injector was used after a timing examination. All patients received 20 ml of Gd-DTPA. Quantitative signal-to-noise (SNR) measurements were obtained at different locations in the thoracic aorta, the pulmonary arteries, and the superior vena cava. Two readers in conference retrospectively evaluated each examination with respect to overall image quality and quality of bolus timing. Bolus timing was considered optimal in 70 cases, and either too early or too late in 11 cases. In 37 examinations the bolus was broadened. The SNR measurements of the thoracic aorta revealed that examinations after bolus testing were significantly superior to examinations without a test bolus (p < 0.001). Signal intensity ratios of the aorta and the pulmonary trunk were significantly higher in examinations with an optimal contrast timing (p < 0.001). Magnetic resonance angiograms of the thoracic aorta with a timing run are significantly superior to non-timed examinations with respect to image quality and SNRs. The administration of 20 ml of Gd-DTPA is sufficient for adult patients.     

Optimal scanning timing by use of multi-detector row computed tomography during thoracic aortography for depiction of arteries causing hemoptysis

Scanning timing for multi-detector row computed tomography during thoracic aortography (MDCT-TA) was explored for depiction of arteries responsible for hemoptysis. The mean time (MT) from contrast medium (CM) injection to peak enhancement (PE) in the descending aorta at the level of the diaphragm on thoracic aortography was investigated. The MT to PE of the descending aorta at the level of diaphragm was 4.86 ± 0.42 s, with 30 mL CM at an injection rate of 10 mL/s. CM injection was completed 1.86 s before the final slice was obtained. The CM injection duration can be calculated as follows: 4.86 s + scan time ? 1.86 s. The optimal scanning timing is a scan delay of approximately 5 s from the start of CM injection, and the CM injection duration is expressed as scan time plus 3 s. MDCT-TA depicted the branching sites of the bronchial arteries in all cases.     

Optimization of contrast material administration for electrocardiogram-gated computed tomographic angiography of the chest

OBJECTIVE: Electrocardiogram-gated computed tomographic angiography is increasingly used in the differential diagnosis of acute chest pain. We studied the optimal timing of contrast material injection using a test bolus and a bolus-tracking technique. MATERIALS AND METHODS: Thirty patients were prospectively included in the study. Volume and flow of high concentration contrast material were adapted to body weight. The scan delay was determined using either a test bolus or a bolus-tracking technique. Attenuation profiles of the different vascular districts were measured to evaluate the timing techniques. RESULTS: In all the patients except for one, an adequate and homogeneous contrast enhancement of more than 200 Hounsfield units (HU) was achieved (285 +/- 45 HU) in the different vascular districts. The pulmonary transit time in the test bolus group was 7 seconds (range, 4-11 seconds). Differences and variability of pulmonary and aortic enhancement were small in both groups (13 +/- 48 HU vs -9 +/- 21 HU), with differences of less than 70 HU over the craniocaudal range and very small intraindividual differences between pulmonary attenuation and systemic attenuation. CONCLUSIONS: Contrast administration regimens for electrocardiogramgated computed tomographic angiography of the chest can be optimized using the bolus-tracking method in the ascending aorta, with a short delay after trigger. Body weight adaptation of volume and injection rate of the contrast material results in a reliable simultaneous opacification of the pulmonary and systemic vasculature.     

Quantitative prediction of contrast enhancement from test bolus data in cardiac MSCT

The purpose of this study was to evaluate a new algorithm for the prediction of contrast enhancement from test bolus data in cardiac multislice spiral computed tomography (MSCT). An algorithm for the prediction of contrast enhancement using test bolus data was developed. A total of 30 consecutive patients (15 male, 69.5 ± 9.6 years) underwent cardiac MSCT (12 × 0.75 mm, 120 kV, 500 mAs_eff.) with a biphasic contrast material injection protocol. Contrast timing was derived from a standard 20 ml test bolus injection. Based on the test bolus time attenuation curves, expected enhancement values were computed for the ascending and descending aorta and the pulmonary trunk and compared with measured data from the cardiac CT scan. At the level of the test bolus measurement in the ascending aorta, the corresponding attenuation values were 309.4 ± 49.6 Hounsfield Units (HU) for the predicted and 285.6 ± 42.6 HU for the measured attenuation, respectively. The mean deviation between predicted and measured CT values was 32.8 ± 48.2 HU (upper and lower limits of agreement 101.4/−53.8 HU), indicating a slight systematic tendency for overestimation. For 80% of the patients the prediction error was less than 50 HU. Prediction of contrast enhancement in cardiac MSCT from test bolus data is feasible with a relatively small mean deviation; 80% of the predictions were within a range that might be acceptable for routine clinical application.     

Waiting to exhale: salvaging the nondiagnostic CT pulmonary angiogram by using expiratory imaging to improve contrast dynamics

We attempted to investigate whether computed tomography pulmonary angiography (CTPA) in the expiratory phase can improve contrast enhancement of the pulmonary arteries and mitigate the effect of inspiratory transient attenuation artifact, potentially salvaging nondiagnostic studies. Eighteen patients with indeterminate inspiratory CTPA, despite proper contrast bolus were studied. Patients were rescanned in expiration using the same contrast bolus and scanning parameters. The attenuation of each pulmonary arterial segment, superior and inferior vena cava, and atria and ventricles during the two phases of respiration was measured independently by three radiologists. All pulmonary segments were evaluated for filling defects during the two phases. In addition, the studies were graded for diagnostic quality of enhancement and probable impact on management. A statistically significant increase in pulmonary arterial enhancement was seen during expiration from the pulmonary trunk to the segmental pulmonary arteries (P < 0.001) and for the inferior vena cava, the right atrium, and the ventricle. The incidence of nondiagnostic inspiratory studies ranged from 89 to 100%, depending on the observer. All studies were upgraded to fully acceptable diagnostic quality with follow-up expiratory imaging (P < 0.0001). Expiratory phase imaging was observed to have diagnostic impact in 78 to 88% of cases, with overall good to moderate interobserver agreement. In one case, pulmonary embolism was detected on the expiratory scan, which was not seen on the inspiratory scan. Expiratory imaging for nondiagnostic CTPA improves pulmonary arterial enhancement and improves diagnostic quality of CTPA by eliminating transient attenuation artifact, thus facilitating more accurate diagnosis and providing earlier treatment of pulmonary embolism.     

多层螺旋CT对肺动脉栓塞的诊断价值

目的:评价多层螺旋CT对急性肺动脉栓塞的诊断价值。方法:22例临床确诊的肺动脉栓塞患者,先行螺旋CT平扫,后经肘静脉注入碘海醇100 ml,延迟15~20 s和25~30 s行两次扫描。结果:平扫的间接征象:肺纹理稀疏11例,肺梗死灶形成9例,肺动脉高压2例,胸膜肥厚3例,胸腔积液8例。增强后的直接征象:充盈缺损(附壁性32支,部分性30支,完全性92支和中心性即轨道征15支)和动脉面细小14支。结论:螺旋CT肺动脉造影是急性肺动脉栓塞安全、迅速、无创伤的有效诊断方法。     

CT pulmonary angiography with a macromolecular contrast medium: a comparative study versus iobitridol in rabbits

RATIONALE AND OBJECTIVES: To compare the pharmacokinetics of a new macromolecular iodinated contrast medium, prototype P743, with a standard contrast agent (iobitridol) for spiral computed tomography pulmonary angiography in rabbits. METHODS: Manual injection was first used to test the performance of P743 even in cases of nonoptimal bolus timing. Then a protocol was designed to compare vessel enhancement in both first-pass and delayed scans for the two contrast agents with the help of a power injector. RESULTS: With manual fast injection, the first pass of iobitridol was observed only on proximal scans. Conversely, opacification of vessels was maintained during three spiral scans with P743 under the same injection conditions. When optimal bolus timing was performed, higher vessel enhancement was observed during bolus first pass with iobitridol (iodine dosage 250 mg I/kg) compared with P743 (150 mg I/kg). However, during the postbolus phase, the decrease in attenuation values was markedly faster with iobitridol than with P743. CONCLUSIONS: This study confirmed that P743 remains more intravascular than iobitridol, which may have clinical implications for the diagnosis of pulmonary embolism, for example.     

Contrast-enhanced thoracic 3D-MR angiography in infants and children

Purpose: To optimise breath-hold contrast-enhanced MR angiography (MRA) in infants and children with suspected congenital heart or thoracic vessel malformation.Material and Methods: Thirty-nine children (median age 1 year) were examined, using five different ultrafast MRA sequences with a TR between 3.2 and 5.0 ms and the contrast agent meglumine gadoterate. A test injection was used to determine contrast travel time. Different parameters for contrast injection were evaluated. Signal-to-noise ratio (SNR) measurements were performed and image quality and injection timing were evaluated.Results: MRA was successful in all patients and image quality was considered very good in 52%. Adequate SNR was achieved with no significant differences between the MR sequences. SNR decreased only 25-30% between subsequent scans. The mean contrast dose was 0.23 mmol/kg. The mean scan time was 12.5±3.8 s; the shorter scan times made dynamic examinations possible with high temporal resolution. Highest spatial resolution was obtained with TR 4.6/5.0 sequences.Conclusion: A contrast dose of 0.2 mmol/kg b.w. is recommended with an injection rate of 0.5 to 1.2 ml/s, depending on patient size and scan time. The scan delay time should equal the contrast travel time for optimal vessel enhancement. In the future, contrast-enhanced MRA may be a potential alternative to angiocardiography in infants and children.     

Biphasic spiral CT of the liver: automatic bolus tracking or time delay?

The aim of this study was to evaluate the value of automatic bolus tracking for biphasic spiral CT of the liver in comparison with time delay examinations. Forty patients scheduled for a biphasic spiral CT of the liver randomly were examined either with time delay of 25 s for the arterial phase and 55 s for the portal-venous phase (n = 20), or with an automatic scan start triggered by contrast enhancement in the aorta (n = 20). Examinations were performed with 120 ml of contrast material and a flow rate of 4.0 ml/s. Density measurements of the aorta, of the liver parenchyma, and of the spleen were obtained by means of regions of interest (ROI). The end of the arterial phase was considered when hepatic parenchymal enhancement was greater than 20 HU. In all patients of the group with automatic bolus tracking arterial scanning was completed in the arterial phase of the liver. In 25 % of patients with fixed time delay, however, an enhancement of liver parenchyma during arterial phase greater than 20 HU was observed. During the portal-venous phase there was no significant difference in parenchymal enhancement between both groups. Automatic bolus tracking allows an individualized timing of the arterial phase in biphasic spiral CT of the liver. The timing is more accurate than in time delay scanning. Received: 18 February 2000 Revised: 13 July 2000 Accepted: 19 July 2000     

Triphasic contrast injection improves evaluation of dual energy lung perfusion in pulmonary CT angiography

Purpose

Lung perfusion analysis at dual energy CT (DECT) is sensitive to beam hardening artifacts from dense contrast material (CM). We compared two scan and four CM injection protocols in terms of severity of artifacts and attenuation levels in the thoracic vessels.

Methods and materials

Data of 120 patients who had undergone dual source dual energy CT pulmonary angiography for suspected acute pulmonary embolism were evaluated. Group 1 (n = 30) was scanned in craniocaudal direction using 64 × 0.6 mm collimation; groups 2–4 (n = 30 each) were scanned in caudocranial direction using 14 × 1.2 mm collimation. In groups 1–3 biphasic injection protocols with different amounts of CM and NaCl were investigated. In group 4 a split-bolus protocol with an initial CM bolus of 50 ml followed by 30 ml of a 70%:30% NaCl/CM mixture and a 50 ml NaCl chaser bolus was used. CT density values in the subclavian vein (SV), superior vena cava (SVC), pulmonary artery tree (PA), and the descending aorta (DA) were measured. Artifacts arising from the SV and SVC on DE pulmonary iodine distribution map were rated on a scale from 1 to 5 (1 = fully diagnostic; 5 = non-diagnostic) by two blinded readers.

Results

In protocol 4 mean attenuation in the SV (645 ± 158 HU) and SVC (389 ± 114 HU) were significantly lower compared to groups 1–3 (p < 0.002). Artifacts in group 4 (1.1 ± 0.4 and 1.5 ± 0.7 for the SV and SVC, respectively) were rated significantly less severe compared to group 1 (3.2 ± 1.0 and 3.0 ± 1.1), 2 (2.6 ± 1.1 and 2.3 ± 1.0) and 3 (1.9 ± 0.9 and 1.9 ± 0.7) (p < 0.01 for all), whereas no significant difference was found between groups 1 and 2 for the subclavian vein (p = 0.07). Attenuation in the PA was also significantly lower in group 4 (282 ± 116 HU) compared to group 1 (397 ± 137 HU), group 2 (376 ± 115 HU) and group 3 (311 ± 104 HU), but still on a diagnostic level.

Conclusion

Split-bolus injection provides sufficient attenuation for pulmonary DECT angiography while beam hardening artifacts arising from high density contrast material in the thoracic vessels can be reduced significantly.     

Optimization of automatic bolus tracking for timing of the arterial phase of helical liver CT

The aim of this study was to optimize bolus tracking for timing of the arterial phase of biphasic helical liver CT and to compare optimized bolus tracking to a standard delay. One hundred fifty patients were examined with six protocols: 5- or 10-s delay after triggering at a threshold of 50 or 75 or 100 HU enhancement in the aorta at the origin of the celiac arteries after injection of 120 ml contrast material at 3 ml/s. Optimal arterial enhancement was defined as 20-30% of hepatic enhancement in portal venous phase. Another 50 patients were examined with the optimized protocol and compared to 50 gender- and age-matched patients who underwent a 25-s standard delay. A 10-s delay after the 75-HU threshold resulted in the most patients with an optimal arterial phase (p < 0.01). Thirty-one of 75 patients examined with this protocol showed optimal early liver enhancement. Bolus tracking compared with standard delay revealed only a trend for a difference (p = 0.07). The outcome of automatic bolus tracking differs depending on the protocol used; however, optimal arterial phase imaging was seen in only 41% of patients, indicating only a trend for superior timing compared with a standard delay.     

Optimal dose and injection duration (injection rate) of contrast material for depiction of hypervascular hepatocellular carcinomas by multidetector CT

Purpose The aim of this study was to investigate the optimal dose and injection duration of contrast material (CM) for depicting hypervascular hepatocellular carcinomas (HCCs) during the hepatic arterial phase with multidetector row computed tomography (CT). Materials and methods The study population consisted of 71 patients with hypervascular HCCs. After unenhanced scans, the first (early arterial phase, or EAP), second (late arterial phase, or LAP), and third (equilibrium phase) scanning was started at 30, 43, and 180 s after injection of contrast material (CM). During a 33-s period, patients with a body weight ≤50 kg received 100 ml of non-ionic CM with an iodine concentration of 300 mg I/ml; patients whose body weight was >50 kg received 100 ml of CM with an iodine concentration of 370 mg I/ml. First, we measured enhancement in the abdominal aorta and tumor-to-liver contrast (TLC) during the EAP and LAP. Next, to investigate the relation between aortic enhancement and TLC during the LAP, two radiologists visually assessed the conspicuity of hypervascular HCCs during the LAP using a 3-point scale: grade 1, poor; grade 2, fair; grade 3, excellent. Finally, to examine the effect of the CM dose and injection duration on aortic enhancement during the EAP, we simulated aortic enhancement curves using test bolus data obtained for 10 HCC patients and the method of Fleischmann and Hittmair. Results A relatively strong correlation was observed between aortic enhancement during the EAP and TLC during the LAP (correlation coefficient r = 0.75, P < 0.001). The 95% confidence intervals for the population mean for aortic enhancement during EAP in patients with tumor conspicuity grades of 1, 2, and 3 were 188.5, 222.4; 228.8, 259.3; and 280.2, 322.5 HU (Hounsfield Unit), respectively. Thus, we considered the lower limit of the aortic enhancement value for excellent depiction of HCCs during EAP to be 280 HU. To achieve an aortic enhancement value of >280 HU for aortic enhancement simulations during EAP, the injection duration should be <25 s for patients receiving a CM dose of 1.7 ml/kg with 300 mg I/ml iodine and <30 s for those receiving 2.0 ml/kg. Conclusions For excellent depiction of hypervascular HCCs during the hepatic arterial phase, the injection duration should be <25 s in patients receiving a CM dose of 1.7 ml/kg with 300 mg I/ml iodine and <30 s for patients receiving 2.0 ml/kg.     

Method for Automatic Tube Current Selection for Obtaining a Consistent Image Quality and Dose Optimization in a Cardiac Multidetector CT

Objective

To evaluate a quantitative method for individually adjusting the tube current to obtain images with consistent noise in electrocardiogram (ECG)-gated CT cardiac scans.

Materials and Methods

The image noise from timing bolus and cardiac CT scans of 80 patients (Group A) who underwent a 64-row multidetector (MD) CT cardiac examination with patient-independent scan parameters were analyzed. A formula was established using the noise correlation between the timing bolus and cardiac scans. This formula was used to predict the required tube current to obtain the desired cardiac CT image noise based on the timing bolus noise measurement. Subsequently, 80 additional cardiac patients (Group B) were scanned with individually adjusted tube currents using an established formula to evaluate its ability to obtain accurate and consistent image noise across the patient population. Image quality was evaluated using score scale of 1 to 5 with a score of 3 or higher being clinically acceptable.

Results

Using the formula, we obtained an average CT image noise of 28.55 Hounsfield unit (HU), with a standard deviation of only 1.7 HU, as opposed to a target value of 28 HU. Image quality scores were 4.03 and 4.27 for images in Groups A and B, respectively, and there was no statistical difference between the image quality scores between the two groups. However, the average CT dose index (CTDIvol) was 30% lower for Group B.

Conclusion

Adjusting the tube current based on timing bolus scans may provide a consistent image quality and dose optimization for cardiac patients of various body mass index values.     

Carotid MR angiography with traditional bolus timing: clinical observations and Fourier-based modelling of contrast kinetics

This study analyses the relation between image quality and contrast kinetics in bolus-timed carotid magnetic resonance angiography (MRA) and interprets the findings by Fourier-based numerical modelling. One hundred patients prone to carotid stenosis were studied using contrast-enhanced carotid MRA with bolus timing. The carotid MRAs were timed to start relatively early without accounting for the injection time of the contrast medium. For interpretation different starting times were modelled, utilising the spectral information of the test bolus series. In the test bolus series the arterial time-to-peak showed a large 95% confidence interval of 12–27 s, indicating the need for individual MRA timing. All bolus-timed MRAs were of good diagnostic quality. The mean (±SD) arterial contrast-to-noise ratio was 53.0 (±12.8) and thus high, and 95% of the MRAs showed a slight venous contamination of 11.8% or less (median 5.6%). According to the Fourier-based modelling the central k-space may be acquired about 2 s before the arterial contrast peak. This results in carotid MRAs with sufficiently high arterial enhancement and little venous contamination. In conclusion, in bolus-timed carotid MRA a relatively short timing provides good arterial contrast with little venous contamination, which can be explained by Fourier-based numerical modelling of the contrast kinetics.     

64层螺旋CT肺动脉成像低管电压设置结合个体化对比剂应用的对照研究

目的 探讨低kV设置及个体化对比剂应用在64层MSCT肺动脉成像(MSCTPA)中应用的可行性.方法 连续选取具有发生肺动脉栓塞可能的高危患者90例,按完全随机设计分为3组:(1)常规组30例,管电压120 kV,对比剂总量70ml;(2)120 kV组30例,管电压120 kV,对比剂总量根据患者体质量进行个体化设置(1.0 ml/kg);(3)100 kV组30例,管电压100 kV,对比剂总量根据患者体质量进行个体化设置(1.0 ml/kg).3组患者的对比剂均在20 s注射完毕,并以相同流率追加生理盐水20ml.对120 kV组和100 kV组CT图像的客观指标、主观图像质量评价、GT容积剂量指数(CTDIvol)和有效吸收剂量(ERD)进行比较;对100 kV组和常规组的对比剂用量、对比剂注射流率、CT图像的客观指标和主观图像质量评价进行比较,以评价64层MSCT低kV设置联合个体化对比剂应用在MSCTPA中应用的可行性.使用方差分析及post hoc检验对3组数据进行统计学分析.结果 图像噪声水平:100 kV组(5.2±1.8)与120 kV组(3.4±0.7)比较增加了52.9%,纵隔窗图像主观图像质量评价差异无统计学意义(q=0.272,P=0.063);CTDIvol:100 kV组[(9.5±0,0)mGy]与120 kV组[(14,6±0,0)mGy]比较下降34,9%;ERD:100 kV组[(2,4±0.4)mSv]与120 kV组[(3.8±0.6)mSv]比较下降36.8%;肺动脉平均CT值:100 kV组[(269.2±54.7)HU]相对于120 kV组[(237.4±62.9)HU]平均增加了13.4%,与常规组比较差异无统计学意义(q=0.172,P=0.260).结论 64层MSCTPA应用低kV设置(100 kV)降低辐射剂量是可行和有效的,个体化对比剂注射方案对特殊人群有一定临床价值.     

Contrast circulation in adult fontan patients using MR Time Resolved Angiography: Application for CT pulmonary angiography

BackgroundWhen patients with Fontan circulation require a computed tomographic pulmonary angiogram (CTPA), there are significant challenges in achieving adequate contrast opacification due to the altered anatomical connections. This study used Time Resolved Angiography with Interleaved Stochastic Trajectories (TWIST) Magnetic Resonance Angiography (MRA) to examine contrast circulation in a cohort of patients with Fontan circulation who were having routine MRI follow up to inform the contrast timing of any subsequent CT.MethodsThis is a single centre, cross-sectional, observational, retrospective study. The time to peak (TTP) signal intensity from the MRA was recorded using regions of interest on the aorta, pulmonary arteries, cavae and Fontan conduit. Patients were grouped by ejection fraction, global longitudinal strain, indexed stroke volume and cardiac index to examine if these cardiac performance parameters affected the mean TTP. Statistical analysis was performed to find the mean TTP for each of the vessels, which was consequently compared between the different cardiac performance parameters.Results35 patients were included in the study. Mean TTP contrast enhancement was 31s in the thoracic aorta, 46s in the right pulmonary artery, 41s in the left pulmonary artery and 55s in the Fontan conduit. Cardiac performance shows no statistically significant relationship to the peak contrast enhancement whether measured by ejection fraction, global longitudinal strain, stroke volume index or cardiac index.ConclusionThe mean optimal timing for a single-phase examination of the Fontan circulation, following an upper limb injection, was 55 s following start of contrast injection irrespective of cardiac performance. In TWIST MRA, the IV bolus is 4–5 s duration. A longer bolus is required for CTA, around 20s, suggesting an additional delay will be required. We propose that an optimal single phase CTPA to be protocolled at 70 s following the start of contrast injection, assuming adequate iodinated contrast dose.     

Late-arterial and portal-venous phase imaging of the liver with a multislice CT scanner in patients without circulatory disturbances: automatic bolus tracking or empirical scan delay?

The value of automatic bolus tracking in late-arterial and portal-venous phase imaging of the liver with a multislice CT scanner as compared with fixed time-delay examination in patients without circulatory disturbances is evaluated. For the evaluation of known or suspected liver disease, 98 multiphase contrast-enhanced CT examinations including double late-arterial phase imaging were randomized into either scanning with a scan delay of 30 s from the beginning of contrast material injection or scanning with automatic bolus tracking. Contrast material was injected at 0.07 ml/kg body weight/s over 30 s. Contrast enhancement in each acquisition was measured in the aorta, portal vein, liver, pancreas and hepatocellular carcinomas. The density difference between hepatocellular carcinomas and the hepatic parenchyma was calculated. The mean time to the first-pass acquisition as determined by automatic bolus tracking was 29.6 s. No statistically significant difference was observed between the two groups either in any enhancement in any acquisition or in the lesion-to-liver density difference. The use of automatic bolus tracking in late-arterial and portal-venous phase hepatic CT does not significantly improve the degree of contrast enhancement in the aorta, portal vein, liver and pancreas or lesion-to-liver conspicuity in patients without circulatory disturbances.