Helical CT of the liver with computer-assisted bolus-tracking technology: scan delay of arterial phase scanning and effect of flow rates

Automatic bolus tracking versus fixed time-delay technique in biphasic multidetector computed tomography of the abdomen

Background

Bolus tracking can individualize time delay for the start of scans in spiral computed tomography (CT).

Objectives

We compared automatic bolus tracking method with fixed time-delay technique in biphasic contrast enhancement during multidetector CT of abdomen.

Patients and Methods

Adult patients referred for spiral CT of the abdomen were randomized into two groups; in group 1, the arterial and portal phases of spiral scans were started 25 s and 55 s after the start of contrast material administration; in group 2, using the automatic bolus tracking software, repetitive monitoring scans were performed within the lumen of the descending aorta as the region of interest with the threshold of starting the diagnostic scans as 60 HU. The contrast enhancement of the aorta, liver, and spleen were compared between the groups.

Results

Forty-eight patients (23 males, 25 females, mean age=56.4±13.5 years) were included. The contrast enhancement of the aorta, liver, and spleen at the arterial phase was similar between the two groups (P>0.05). Regarding the portal phase, the aorta and spleen were more enhanced in the bolus-tracking group (P<0.001). The bolus tracking provided more homogeneous contrast enhancement among different patients than the fixed time-delay technique in the liver at portal phase, but not at the arterial phase.

Conclusions

The automatic bolus-tracking method, results in higher contrast enhancement of the aorta and spleen at the portal phase, but has no effect on liver enhancement. However, bolus tracking is associated with reduced variability for liver enhancement among different patients.

Patient body weight-tailored contrast medium injection protocol for the craniocervical vessels: a prospective computed tomography study

OBJECTIVES

To evaluate body weight-tailored contrast medium (CM) administration for computed tomography angiography (CTA) of the craniocervical vessels.

METHODS

Institutional review board approval was obtained, and all patients gave written informed consent. Sixty patients were consecutively assigned to one of three dose groups (20 patients per group) with CM doses of Visipaque 270® (iodixanol 270 mg/ml) tailored to body weight at doses of 1.5, 1.0, or 0.5 ml/kg. Region-of-interest (ROI) analysis of maximum enhancement (ME) was conducted, and signal-to-noise-ratios (SNR) and contrast-to-noise-ratios (CNR) were calculated. Retrospective comparison was performed with three matched control groups examined with a standard CM dose (80 ml of Visipaque 270®). Image quality was rated by two neuroradiologists blinded to the CM dose used. Interrater reliability was calculated using kappa statistics.

RESULTS

Body weight/BMI and ME were inversely correlated in the three control groups receiving the standard dose (r = -0.544/-0.597/-0.542/r = -0.358/r = -0.424/r = -0.280). Compared to standard dose, 1.5 ml/kg produced higher ME, SNR, and CNR in the anterior circulation (p≤0.038), 1.0 ml/kg had higher ME in cervical and medium-sized cerebral arteries (p≤0.034), and 0.5 ml/kg had lower ME, SNR and CNR for medium-sized cerebral arteries (p≤0.049). ME, SNR, and CNR were the same for 1.5 ml/kg and 1.0 ml/kg (p≥0.24), and both had higher values compared to 0.5 ml/kg (p≤0.043/p≤0.028). In patients with BMI>25, 1.5 ml/kg and 1.0 ml/kg produced higher ME than standard dose (p<0.001/p = 0.008), but ME in patients with BMI>25 did not differ between group 1 and group 2 (p = 0.673). In patients with BMI≤25, 1.5 ml/kg and 1.0 ml/kg produced ME comparable to standard dose (p = 0.132/p = 0.403). Regardless of patient weight, 0.5 ml/kg yielded lower ME than standard dose (p = 0.019/0.002).

CONCLUSIONS

Craniocervical CTA with a body weight-tailored CM dose of 1.0 ml/kg (270 mg iodine/ml) reduces iodine load in patients weighing <80 kg while producing ME similar to standard dose and improves ME in patients with BMI>25.

Intravenous contrast medium administration and scan timing at CT: considerations and approaches

The continuing advances in computed tomographic (CT) technology in the past decades have provided ongoing opportunities to improve CT image quality and clinical practice and discover new clinical CT imaging applications. New CT technology, however, has introduced new challenges in clinical radiology practice. One of the challenges is with intravenous contrast medium administration and scan timing. In this article, contrast medium pharmacokinetics and patient, contrast medium, and CT scanning factors associated with contrast enhancement and scan timing are presented and discussed. Published data from clinical studies of contrast medium and physiology are reviewed and interpreted. Computer simulation data are analyzed to provide an in-depth analysis of various factors associated with contrast enhancement and scan timing. On the basis of basic principles and analysis of the factors, clinical considerations and modifications to protocol design that are necessary to optimize contrast enhancement for common clinical CT applications are proposed.

Triple-phase computed tomography during arterial portography with bolus tracking for hepatic tumors

PURPOSE

The purpose of this study was to assess the usefulness of triple-phase computed tomography during arterial portography (CTAP) using a bolus-tracking technique.

MATERIAL AND METHODS

The subjects were 60 patients with hepatic tumors: 20 patients with metastatic liver tumors with a normal liver and 40 with hypervascular hepatocellular carcinoma (HCC) with liver cirrhosis. The region of interest was set in the portal vein, and CTAP was automatically started after the triggering threshold (180 HU) was reached. Three scans were performed: early phase (E), hepatic parenchymal phase (HP), and late phase (L). The scan start time of E-CTAP was measured. The detection rates of the HCC nodules were evaluated during each CTAP phase.

RESULTS

CTAP was performed by bolus tracking without failure in any of the patients. The mean scan start times in the normal liver group and liver cirrhosis group were 14.3 +/- 1.34 s and 18.5 +/- 2.46 s, respectively, which were significantly different from each other. The detection rates of HCC nodules for E-CTAP, HP-CTAP, and L-CTAP were 29.6%, 100%, and 83.3%, respectively.

CONCLUSION

The bolus-tracking technique enabled us to perform CTAP with optimal timing regardless of the portal blood flow dynamics.

Aortic and hepatic contrast enhancement with abdominal 64-MDCT in pediatric patients: effect of body weight and iodine dose

OBJECTIVE

The purpose of our study was to retrospectively evaluate the effect of body weight and iodine dose on aortic and hepatic contrast enhancement in pediatric patients who underwent 64-MDCT of the abdomen and pelvis.

MATERIALS AND METHODS

Eighty-seven consecutive pediatric patients (50 boys and 37 girls; median age, 12.1 years; age range, 3.8-17.6 years) underwent standard abdominopelvic CT with a 64-MDCT scanner. Contrast medium (350 mg I/mL) was injected using a power injector at 2 mL/s followed by 15-20 mL of saline flush. According to our CT protocol, the volume of administered contrast medium was approximately 1.8 mL/kg of body weight, up to the maximum volume of 80 mL. CT scanning was initiated 60 seconds after the start of the contrast medium injection. CT attenuations of the aorta and liver were measured. For each patient, the injected contrast medium iodine mass per body weight index (g I/kg) (hereafter, iodine mass body index) was calculated. Linear regression analysis was performed between iodine mass body index and aortic and hepatic attenuations.

RESULTS

A wide range of patient weights (19-82 kg; mean, 48.6 kg [95% CI, 45.3-51.9 kg]) and contrast volumes (30-80 mL; median, 80.0 mL) were observed. The median attenuations were 149.0 HU (141.0-160.0 HU) for the aorta and 113.5 HU (109.5-120.0 HU) for the liver. Moderately high correlations were observed between iodine mass body index and aortic (Spearman's rho [r(s)] = 0.60 [0.45-0.72]; p < 0.001) and hepatic (r(s) = 0.60 [0.42-0.70]; p < 0.001) attenuations. The regression formulae for aortic attenuation (58.4 + 176.3 x iodine mass body index [p < 0.001]) and hepatic attenuation (58.7 + 108.5 x iodine mass body index [p < 0.001]) indicate that 1.5 and 1.8 mL/kg (350 mg I/mL) of contrast media are required to achieve 116 and 127 HU, respectively, of contrast-enhanced attenuation in the liver.

CONCLUSION

In our study, using abdominal 64-MDCT in pediatric patients, we found that approximately 1.5 mL/kg, or 0.525 g I/kg, yields 116 HU of hepatic attenuation or 50-55 HU of hepatic enhancement.

Detection of hypervascular hepatocellular carcinoma with multidetector-row CT: single arterial-phase imaging with computer-assisted automatic bolus-tracking technique compared with double arterial-phase imaging

PURPOSE

To compare single arterial-phase (SAP) computed tomography (CT) imaging with bolus tracking (BT) with double arterial-phase (DAP) CT imaging for detecting hypervascular hepatocellular carcinoma.

MATERIALS AND METHODS

The DAP images were obtained at 25 (DAP-early) and 40 seconds (DAP-late) after the start of contrast material injection. All patients underwent SAP-BT imaging where images were obtained 10 seconds after the CT attenuation value of the aorta reached the threshold value of 120 Hounsfield unit (HU) in 29 (group 120-HU), 160 HU in 30 (group 160-HU), and 200 HU in 32 patients (group 200-HU). Attenuation conspicuity with SAP-BT technique was compared with that with DAP technique using repeated-measures analysis of variance. Attenuation conspicuity and mean scan delays with SAP-BT images obtained with different threshold values were compared using analysis of variance. The sensitivities were compared using McNemar and Fisher exact tests.

RESULTS

Within all groups, mean attenuation conspicuity with SAP-BT and DAP-late was significantly higher than that with DAP-early. Regarding SAP-BT, mean attenuation conspicuity in group 200-HU (42 +/- 18 HU) was significantly higher than those in groups 120-HU (23 +/- 11 HU) and 160-HU (25 +/- 11 HU). Mean scan delays for SAP-BT were 24.2 seconds in group-120 HU, 26.8 seconds in group-160 HU, and 31.1 seconds in group-200 HU (P < 0.001). The mean sensitivity with SAP-BT technique in group 200-HU (92.7%) was significantly higher than those in groups 120-HU (72.4%) and 160-HU (71.1%).

CONCLUSIONS

Single arterial-phase CT scanning with bolus tracking can be effectively used to detect hepatocellular carcinoma when a threshold value of 200 HU is used.

Patient-specific Time to Peak Abdominal Organ Enhancement Varies with Time to Peak Aortic Enhancement at MR Imaging

PURPOSE

To retrospectively evaluate the relationship between the times to peak enhancement of the liver, pancreas, and jejunum with respect to the time to peak aortic enhancement at magnetic resonance (MR) imaging.

MATERIALS AND METHODS

The committee on human research approved this study and waived written informed consent. This study was HIPAA compliant. The study retrospectively identified 141 patients (63 men, 78 women; mean age, 57 years) who underwent abdominal MR imaging by using a test bolus that was monitored approximately every second for 2 minutes with a spoiled gradient-echo T1 transverse section through the upper abdomen. The times to peak enhancement of the aorta, liver, pancreas, and jejunum were recorded and correlated with the time to peak aortic enhancement, age, and sex by means of univariate and multivariate linear regression analyses.

RESULTS

The mean time to peak aortic enhancement was 21.1 seconds (range, 8.7-41.8 seconds). The times to peak enhancement of the liver, pancreas, and jejunum were positively and linearly correlated with the time to peak aortic enhancement (r = 0.69, 0.86, and 0.80, respectively, all P < .001) and were 3.39, 1.64, and 2.04 times longer than the time to peak aortic enhancement, respectively. Age, sex, and history of heart disease did not give additional predictive information for determining the time to peak visceral enhancement.

CONCLUSION

The times to peak enhancement of the liver, pancreas, and jejunum are linearly related to that of the aorta. These results could potentially allow tailored patient- and organ-specific scan delay optimization at contrast material-enhanced MR image evaluation.

MDCT Angiography of the Pulmonary Arteries: Influence of Body Weight, Body Mass Index, and Scan Length on Arterial Enhancement at Different Iodine Flow Rates

OBJECTIVE

The purpose of this study was to assess whether body weight, body mass index, and scan length influence arterial enhancement during CT angiography (CTA) of the pulmonary arteries at different iodine flow rates.

MATERIALS AND METHODS

CTA examinations of the pulmonary arteries performed for routine clinical care of 120 patients between March and December 2003 were retrospectively evaluated. Patients had received either 120 mL of contrast medium with an iodine concentration of 300 mg I/mL (group A) or 90 mL of contrast medium with an iodine concentration of 400 mg I/mL (group B). The iodine dose was 36 g, and the injection rate was 4 mL/s in all examinations. The iodine flow rate was 1.2 g I/s in group A and 1.6 g I/s in group B. Arterial attenuation along the z-axis was measured per patient, and the influence of body weight, body mass index, and scan length on enhancement of the pulmonary arteries in the two groups was assessed.

RESULTS

In group A and in group B, body weight and body mass index correlated significantly with mean enhancement along the z-axis (r = -0.35 and -0.26 for group A and -0.48 and -0.40 for group B). Scan length showed no correlation with pulmonary attenuation. Mean pulmonary artery enhancement was significantly higher in group B with a difference of 51 H compared with group A.

CONCLUSION

Pulmonary artery attenuation in CTA of the pulmonary arteries shows a small but significant correlation with body weight and body mass index independently of the iodine flow rate used. A higher iodine flow rate improves pulmonary artery enhancement.

MDCT of the Liver and Hypervascular Hepatocellular Carcinomas: Optimizing Scan Delays for Bolus-Tracking Techniques of Hepatic Arterial and Portal Venous Phases

OBJECTIVE

The purpose of our study was to determine the optimal scan delays required for hepatic arterial and portal venous phase imaging and for the detection of hypervascular hepatocellular carcinomas (HCCs) in contrast-enhanced MDCT of the liver using a bolus-tracking program.

SUBJECTS AND METHODS

CT images (2.5-mm collimation, 5-mm thickness with no intersectional gap) detected an increase in the CT value of 50 H in the lower thoracic aorta. The images were obtained after an IV bolus injection of 2 mL/kg of nonionic iodine contrast material (300 mg I/mL) at 4 mL/s in 171 patients, who were prospectively randomized into three groups with scans commencing at 5, 20, and 45 seconds; 10, 25, and 50 seconds; and 15, 30, and 55 seconds for the first (acquisition time: 4.3 seconds), second (4.3 seconds), and third (9.1 seconds) phases, respectively, after a bolus-tracking program. CT values of the aorta, spleen, proximal portal veins, liver parenchyma, and hepatic veins were measured. Increases in CT values from unenhanced to contrast-enhanced CT were assessed using a contrast enhancement index (CEI). Spleen-to-liver and HCC-to-liver contrasts were also assessed. A qualitative degree of contrast enhancement in each organ was prospectively assessed by two independent radiologists.

RESULTS

At 10-15 seconds, the CEI of the aorta reached 300-336 H and that of the spleen reached 97-108 H without significant enhancement of liver parenchyma (15-25 H). The CEI of the proximal portal veins moderately increased (75-104 H) at 10-15 seconds, but no significant enhancement of hepatic veins was observed (24-51 H). The CEI of liver parenchyma peaked (59-63 H) at 45-55 seconds, when the CEIs of the aorta (117-125 H) and spleen (73-82 H) decreased. Spleen-to-liver contrast (81-84 H) was highest at 10-20 seconds and HCC-to-liver contrast (39-44 H) was highest at 10-15 seconds. The qualitative results correlated well with quantitative results.

CONCLUSION

The optimal scan delays for hepatic arterial and portal venous phases after the bolus-tracking program detected threshold enhancement by 50 H in the lower thoracic aorta for the detection of hypervascular HCCs were 10-15 and 45-55 seconds, respectively.

Imaging liver metastases: review and update

The radiologic diagnosis of liver metastasis involves detection, characterization, and tumor staging. Knowledge of the histopathologic changes that occur with metastases provides the best approach to the accurate interpretation of radiologic imaging findings, and in particular, radiologists need to choose appropriate imaging methods based on such knowledge. Because the majority of metastases are hypovascular, the merits of the routine acquisition of hepatic arterial dominant-phase images by contrast-enhanced computed tomography (CT) or magnetic resonance imaging (MRI) are disputable. Hepatic arterial dominant-phase images may be obtained when hypervascular tumors are suspected or three-dimensional CT angiography is necessary. And, imaging during the portal venous phase is essential for detecting metastases, evaluating intrahepatic vessel invasion, and for assessing intratumoral necrosis or fibrosis. Equilibrium- to delayed-phase imaging 3-5 min after contrast administration may improve the detection of intratumoral fibrosis, and occasionally lead to more accurate tissue characterization. MRI offers diagnostic information on vascularity, amount of free water, hemorrhage, fibrosis, necrosis, and water molecule diffusion in metastases. And, liver-specific contrast agents like superparamagnetic iron oxide, liposoluble gadolinium chelate, and manganese may improve the MRI-based diagnosis of liver metastases.

Variation of the Time to Aortic Enhancement of Fixed-Duration Versus Fixed-Rate Injection Protocols

OBJECTIVE

The objective of the study was to clarify whether a fixed-duration injection protocol is useful in determining the optimal scan delay time without the need for a bolus-tracking technique.

MATERIALS AND METHODS

Three hundred eighteen patients underwent a helical CT examination using a bolus-tracking technique. All the examinations were performed after administering a nonionic contrast medium (300 or 370 mg I/mL; 2 mL/kg of body weight for patients weighing < or = 75 kg, 150 mL for those weighing > 75 kg). The patients were assigned to one of three groups according to the injection protocol. The injection rate was alternated to 3 or 4 mL/sec in group 1. The injection duration was 38 or 47 sec in groups 2 and 3, respectively. The aortic arrival time and the 100-H threshold time in each patient were measured. The mean values and the variations in the aortic arrival time and 100-H threshold time according to the injection protocols and the contrast media were compared.

RESULTS

The mean variations (+/- SD) of aortic arrival times and 100-H thresholds in group 2 (aortic arrival time = 16.1 +/- 2.7 sec, 100-H threshold time = 19.6 +/- 2.9 sec) were smaller than in groups 1 (16.3 +/- 3.0 sec and 19.9 +/- 3.7 sec, respectively) and 3 (16.8 +/- 3.5 sec and 20.4 +/- 4.1 sec, respectively). However, the range of aortic arrival times and 100-H threshold times was more than 10 sec for all groups. The mean aortic arrival time and 100-H threshold time for all patients were 16.5 and 20.0 sec, respectively, and did not vary significantly with the injection protocol and concentration of contrast medium.

CONCLUSION

The individual variations of the aortic arrival and 100-H threshold times can be reduced using a fixed-duration injection technique, but there are still substantial variations. Therefore, a bolus-tracking technique is recommended for optimal timing of arterial phase scanning.

[Method for determining scan timing based on analysis of formation process of the time-density curve]

A strict determination of scan timing is needed for dynamic multi-phase scanning and 3D-CT angiography (3D-CTA) by multi-detector row CT (MDCT) . In the present study, contrast media arrival time (T(AR)) was measured in the abdominal aorta at the bifurcation of the celiac artery for confirmation of circulatory differences in patients. In addition, we analyzed the process of formation of the time-density curve (TDC) and examined factors that affect the time to peak aortic enhancement (T(PA)). Mean T(AR) was 15.57+/-3.75 s. TDCs were plotted for each duration of injection. The rising portions of TDCs were superimposed on one another. TDCs with longer injection durations were piled up upon one another. Rise angle was approximately constant in response to each flow rate. Rise time (T(R)) showed a good correlation with injection duration (T(ID)). T(R) was 1.01 TID (R(2)=0.994) in the phantom study and 0.94 T(ID)-0.60 (R(2)=0.988) in the clinical study. In conclusion, for the selection of optimal scan timing it is useful to determine T(R) at a given point and to determine the time from T(AR).

Role of multiphase scans by multirow-detector helical CT in detecting small hepatocellular carcinoma

AIM: To evaluate the role of multiphasic scanning by multirow-detector helical CT (MDCT) in detecing small hypervascular hepatocellular carcinoma (SHCC).

METHODS: Multiphasic scanning was carried out in 75 patients with SHCC with Marconi MX8000 CT scanner. The early arterial phase (EAP), late arterial phase (LAP) and the portal venous phase (PVP) scans were started at 21 s, 34 s and 85 s respectively. The mean difference of CT values between tumor and liver parenchyma for each scanning phase was measured, and the sensitivity of detection of SHCC in each of these phases and in the combined phase was calculated and statistically analyzed.

RESULTS: The mean difference of CT values between tumor and liver parenchyma was significant in 71 lesions ≥ 1 cm in three phases (P < 0.05). In 91 tumor foci, the detectability of SHCC was 45.1%, 83.5% and 92.3% in EAP, LAP and double arterial phases (DAP), respectively. The early arterial phase plus the portal venous phase and the double arterial phase plus the portal venous phase were 94.5%, 97.8%, respectively. Whereas the detectability in LAP plus PVP and in DAP plus PVP had no statistical difference.

CONCLUSION: The utility of faster speed and thinner slice MDCT and multiphase scanning protocol can improve the detectability of hypervascular small hepatocellular carcinoma. Among which LAP is superior to EAP in depicting the lesions.

Evaluation of optimal timing of arterial phase imaging for the detection of hypervascular hepatocellular carcinoma by using triple arterial phase imaging with multidetector-row helical computed tomography

PURPOSE

We evaluated the optimal timing of arterial phase imaging for detection of hypervascular hepatocellular carcinoma by using triple arterial phase imaging with multidetector-row helical computed tomography.

MATERIALS AND METHODS

Forty-nine patients with 90 hypervascular hepatocellular carcinomas (3 to 50 mm in diameter; mean, 18.7 mm) underwent triple arterial phase imaging of the whole liver using a multidetector-row helical computed tomography. At 20 seconds, 30 seconds, and 40 seconds after intravenous administration of 100 mL of 300 mgI/mL of nonionic contrast medium at a rate of 4 mL/s, early, middle, and late arterial phase images were obtained serially during a single breath-hold with an interscan delay of 5 seconds. Detector-row configurations of 4 mm x 4, scan pitch of 5.5, and scan time of 5 seconds for each phase were used. Forty prospective reconstruction images of 5-mm thickness for each phase were obtained. The images from each phase were interpreted separately for detection of hypervascular hepatocellular carcinoma by 3 observers independently who were unaware of tumor burden in the liver. Sensitivity, positive predictive value, and area under the receiver operating characteristic curve values for each arterial phase were calculated and compared statistically.

RESULTS

The mean sensitivity and positive predictive values for hypervascular hepatocellular carcinoma diagnosis of blind readers were 37% and 87% for the early arterial phase, 73% and 85% for the middle arterial phase, and 49% and 81% for the late arterial phase, respectively. The middle arterial phase imaging showed significantly superior sensitivity compared with the early and late arterial phase for detecting hepatocellular carcinoma (P < 0.05). Mean area under the receiver operating characteristic curve value of the middle arterial phase imaging (0.84) was significantly higher that that of the early (0.56) or late arterial phase (0.62; P < 0.05).

CONCLUSION

If a single arterial phase is used for diagnosis of hypervascular hepatocellular carcinoma, the middle phase (delay time of 30 seconds) is optimal.

Three-dimensional CT angiography of the hepatic artery: use of multi-detector row helical CT and a contrast agent

The administration of a contrast agent to obtain optimal images at three-dimensional computed tomographic (CT) angiography of the hepatic artery by using multi-detector row helical CT was investigated. Three-dimensional CT angiographic images were evaluated visually, and quantitative evaluation was performed by measuring the postcontrast CT number of the aorta. The injection rate of 5 mL/sec was significantly superior to that of 4 mL/sec in both evaluations. At administration of a contrast agent with 300 or 350 milligrams of iodine per milliliter, there were no significant differences in either evaluations. The preferable injection rate to obtain sufficient three-dimensional CT angiographic data was 5 mL/sec.

Evaluation of aortoiliac aneurysm before endovascular repair: comparison of contrast-enhanced magnetic resonance angiography with multidetector row computed tomographic angiography with an automated analysis software tool

PURPOSE

The purpose of this study was to assess accuracy and reliability of a volumetric analysis of abdominal aneurysms on the basis of multidetector row computed tomographic angiography (CTA) and magnetic resonance angiography (MRA) with a commercially available automated vessel analysis software program.

MATERIALS AND METHODS

Twenty patients with abdominal aortic aneurysms underwent preoperative CTA and MRA before endovascular repair. Postdeployment CTA was performed in 15 of these 20 patients (75%). All preoperative CTA and MRA and postdeployment CTA data sets were analyzed with an automated software tool. The length of the stent grafts on postdeployment CTA was measured and compared with the true length of the primary component. Two readers independently evaluated 13 vessel parameters on preoperative CTA and MRA, which are considered to be important in planning stent graft deployment.

RESULTS

With the automated analysis software tool, all measurements could be performed on either CTA or MRA data sets. There was no statistically significant difference between postdeployment measurements of stent graft length on CTA and the true dimensions of the implanted stent grafts. Interobserver agreement for all of the measurements with either CTA or MRA was good to excellent (interclass coefficient, 0.71 to 0.99) with only minimal mean differences of measured dimensions between both readers (range, -2.0 to +2.3 mm, Bland-Altman). Intermodality agreement between CTA and MRA was good to excellent (interclass coefficient, 0.62 to 0.98) with small mean differences of measured dimensions between both methods (range, -4.1 to +2.1 mm, Bland-Altman).

CONCLUSION

Volumetric measurement with an automated analysis software tool allows a fast, precise, and reliable noninvasive preoperative determination of all aortic dimensions on the basis of either CTA or MRA data sets.

CT angiography of the arterial system

CTA has become an important diagnostic tool in the evaluation of vascular diseases in virtually all parts of the body. Whereas CTA is able to provide images depicting exquisite anatomic detail, careful scanning technique and selection of scan parameters are critical for high quality studies. The choices to be made when prescribing a scan can seem daunting at first, but if one applies the principles outlined previously, CTA can be a relatively easy, fast, and safe diagnostic technique that is effective in the majority of patients with vascular disease.

Parameters affecting bolus geometry in CTA: a review

CT angiography (CTA) is based on acquisition of data during the arterial phase of contrast material passage. CTA needs timing of the contrast bolus, which should be based on accurate knowledge of bolus geometry. Experimental and human studies on bolus geometry and bolus timing in CTA were reviewed. Important parameters of bolus geometry and methods of bolus timing (test bolus and bolus tracking) are described. Recommendations are given for an optimal CTA protocol.

Small hypervascular hepatocellular carcinoma revealed by double arterial phase CT performed with single breath-hold scanning and automatic bolus tracking

OBJECTIVE

The purpose of this study was to evaluate the usefulness of double arterial phase CT for the detection of small hypervascular hepatocellular carcinomas, using an automated bolus-tracking technique to initiate the hepatic arterial phase CT.

MATERIALS AND METHODS

Double arterial and late phase contrast-enhanced helical CT scans were obtained on 287 consecutive patients suspected of having hepatocellular carcinoma. These included 56 patients with 90 small (< or 3 cm) hepatocellular carcinomas and 50 patients with no hepatocellular carcinomas. CT scans of these patients were interpreted by three reviewers. The first arterial phase scan was initiated automatically 10 sec after the bolus-tracking program detected the threshold enhancement of 50 H in the abdominal aorta. Three reviewers interpreted the late phase CT scans in combination with the first, second, or both hepatic arterial phases. Measures of the reviewers' detection of hepatocellular carcinoma included analysis of interobserver variation, sensitivity, specificity, and area under receiver operating characteristic curve (A(z)).

RESULTS

The time elapsed from bolus initiation to threshold aortic enhancement ranged from 10 to 24 sec (mean, 13 sec), resulting in initiation of the first arterial phase CT scan from 20 to 34 sec (mean, 23 sec). The combination of late phase CT and both first and second arterial phase images showed significantly better performance than the combination of the late phase and either the first or second arterial phases, although the difference was most evident in comparison with the combination of second arterial and late phases.

CONCLUSION

An automated bolus-tracking program can be used to optimize the timing of hepatic arterial phase CT. Multiphasic CT performed using this technique is useful in detection of small hepatocellular carcinoma.