Peak Aortic Enhancement Research Articles

Computation of contrast-enhanced perfusion using only two CT scan phases: a proof-of-concept study on abdominal organs

BackgroundComputed tomography perfusion imaging (CTPI) by repeated scanning has clinical relevance but implies relatively high radiation exposure. We present a method to measure perfusion from two CT scan phases only, considering tissue enhancement, feeding vessel (aortic) peak enhancement, and bolus shape.MethodsCTPI scans (each with 40 frames acquired every 1.5 s) of 11 patients with advanced hepatocellular carcinoma (HCC) enrolled between 2012 and 2016 were retrospectively analysed (aged 69 ± 9 years, 8/11 males). Perfusion was defined as the maximal slope of the time-enhancement curve divided by the peak enhancement of the feeding vessel (aorta). Perfusion was computed two times, first using the maximum slope derived from all data points and then using the peak tissue enhancement and the bolus shape obtained from the aortic curve.ResultsPerfusion values from the two methods were linearly related (r2 = 0.92, p < 0.001; Bland–Altman analysis bias -0.12). The mathematical model showed that the perfusion ratio of two ROIs with the same feeding vessel (aorta) corresponds to their peak enhancement ratio (r2 = 0.55, p < 0.001; Bland–Altman analysis bias -0.68). The relationship between perfusion and tissue enhancement is predicted to be linear in the clinical range of interest, being only function of perfusion, peak feeding vessel enhancement, and bolus shape.ConclusionsThis proof-of-concept study showed that perfusion values of HCC, kidney, and pancreas could be computed using enhancement measured only with two CT scan phases, if aortic peak enhancement and bolus shape are known.

Effect of decreased contrast injection flow rate on aortic enhancement in 80-KV peak CT with contrast dose reduction.

Effect of decreased injection flow rate of contrast agent at the same iodine dose and delivery rate on aortic enhancement has not been clearly elucidated. To evaluate the effect of decreased injection flow rate of contrast agent on aortic peak enhancement in a dynamic flow phantom and on aortic enhancement in clinical dynamic 80-kVp computed tomography (CT) with contrast dose reduction. In the dynamic flow phantom experiment, the effect of a decreased injection flow rate at the same total iodine dose and delivery rate on simulated aortic peak enhancement was evaluated. In the clinical retrospective study, we searched 312 patients with renal dysfunction who underwent an 80-kVp abdominal dynamic CT with 40% reduction of contrast agent from a standard 120-kVp protocol and measured the aortic enhancement at the level of the hepatic hilum. Independent predictors for aortic enhancement were determined by multiple linear regression analysis, and after adjustment of significant predictors, independent variables for acquiring optimal aortic enhancement, ≥300 HU, were determined by multiple logistic regression analysis. In the phantom experiment, decreased flow rate showed a significant but small descent effect (6%-9%) on simulated aortic peak enhancement. In the multiple linear regression analysis, only age was an independent predictor of aortic enhancement; there was no independent predictor for optimal age-adjusted aortic enhancement of ≥300 HU. Decreased injection flow rate had a small influence on aortic enhancement in vitro but had no significant effect on the aortic enhancement in clinical dynamic 80-kVp CT.

Contrast Saline Mixture DualFlow Injection Protocols for Low-Kilovolt Computed Tomography Angiography: A Systematic Phantom and Animal Study.

The aim of this study was to evaluate a contrast media (CM)-saline mixture administration with DualFlow (DF) to adapt injection protocols to low-kilovolt (kV) computed tomography angiography (CTA). In both a circulation phantom and animal model (5 Goettingen minipigs), 3 injection protocols were compared in dynamic thoracic CTA: (a) DF injection protocol at 80 kV with a iodine delivery rate (IDR) of 0.9 gI/s, a flowrate of 5 mL/s injected with a 60%/40% ratio of iopromide (300 mgI/mL) and saline (dose contrast medium 180 mgI/kg body weight [BW]); (b) reference CTA was performed at 120 kV and a 40% higher iodine dose applied at higher IDR (1.5 gI/s, 5 mL/s iopromide [300 mgI/mL]; no simultaneously administered saline; 300 mgI/kg BW); and (c) conventional single-flow (SF) protocol with identical IDR as the DF protocol at 80 kV (0.9 gI/s, 3 mL/s iopromide [300 mgI/mL]; no simultaneously administered saline; 180 mgI/kg BW). All 3 injection protocols are followed by a saline chaser applied at the same flow rate as the corresponding CM injection. Time attenuation curves representing the vascular bolus shape were generated for pulmonary trunk and descending aorta. In the circulation phantom, pulmonary and aortic time attenuation curves for the 80 kV DF injection protocols do not significantly differ from the 80 kV SF and the 120 kV SF reference. In the animal model, the 80 kV DF protocol shows similar pulmonal and aortic peak enhancement when compared with the 120 kV SF and 80 kV SF protocols. Also, the bolus length above an attenuation level of 300 HU reveals no significant differences between injection protocols. However, the time to peak was significantly shorter for the 80 kV DF when compared with the 80 kV SF protocol (15.78 ± 1.9 seconds vs 18.24 ± 2.0 seconds; P = 0.008). DualFlow injection protocols can be tailored for low-kV CTA by reducing the IDR while overall flow rate remains unchanged. Although no differences in attenuation were found, DF injections offer a shorter time to peak closer to the reference 120 kV protocol.This allows the use of DF injection protocols to calibrate bolus density in low-kV CTA and yields the potential for a more individualized CM administration.

Feasibility of wide detector three-pass arterial phase liver CT in patients with cirrhosis: timing of hyperenhancing lesion peak conspicuity.

To evaluate feasibility of a wide detector liver CT protocol with three acquisitions in the hepatic arterial phase. Forty-one patients with cirrhosis prospectively underwent a wide detector axial liver CT protocol. Three 16cm axial liver acquisitions were obtained during a single breath hold at peak aortic enhancement plus 10, 20, and 25s. Two readers working separately scored overall exam quality, identified hyperenhancing lesions, and subjectively scored and ranked relative lesion conspicuity. Objective lesion enhancement was measured and CNR calculated. Data were analyzed using a generalized linear models and Tukey's post hoc testing. Seventy-one hyperenhancing lesions were identified with average size of 1.8cm (range 0.4-9.6cm). The two readers separately identified 60 and 54 lesions on the 10s arterial acquisition, 70 and 67 on the 20s, and 52 and 51 on the 25s. The readers determined all exams had diagnostic image quality. Subjective ranking of lesion conspicuity was greatest at 20s in 62% of lesions but was greatest at 10 or 25s in 38%. CNR was highest at 20s in 58% of lesions but was highest at 10 or 25s in 42%. Overall, there was no significant difference in mean CNR between the three arterial acquisitions. A wide detector axial liver CT protocol with three acquisitions in the hepatic arterial phase is technologically feasible and results in diagnostic image quality. With this protocol, peak subjective and objective hyperenhancing lesion conspicuity may be earlier or later than 20s in up to 40% of lesions.

Dose Optimization of Perfusion-derived Response Assessment in Hepatocellular Carcinoma Treated with Transarterial Chemoembolization: Comparison of Volume Perfusion CT and Iodine Concentration

We assessed the value of iodine concentration (IC) as a perfusion-derived response marker for hepatocellular carcinoma (HCC) treated with transarterial chemoembolization (TACE) in comparison with volume perfusion computed tomography (VPCT) parameters. Forty-one HCC lesions in 32 patients examined before and after TACE were analyzed retrospectively. VPCT-parameters were calculated and lesion iodine-maps were computed using subtraction of the baseline and the scan 7 seconds after aortic peak enhancement from the corresponding 80 kVp-VPCT data set. Modified RECIST was used as standard response criteria. Comparisons were performed using Student's t test for normal distributed data and Mann-Whitney U test for non-normal distributed data. Additionally, correlation analysis, receiver operating characteristics (ROC) and interreader agreement were assessed. In responding lesions, mean pre-TACE IC and blood flow (BF) were 131.2 mg/100 mL and 96.7 mL/100 mL/min, decreasing to IC 25.6 mg/100 mL (P < 0.001) and BF 28.5 mL/100 mL/min (P < 0.001) post-TACE. In nonresponding lesions, the values remained almost unchanged: pre-TACE: mean BF 79.3 mL/100 mL/min and mean IC 90.4 mg/100 mL; post-TACE: mean BF 71.3 mL/100 mL/min (n.s.) and mean IC 105.4 mg/100 mL (n.s.). Differences in IC-values revealed a high sensitivity/specificity of 96.7%/81.8%. IC and VPCT-parameters showed strong, positive correlations. Mean volume CT dose index for VPCT was 63.4 mGy and 4.9 mGy for iodine maps. Thus, IC is a meaningful perfusion marker for local therapy response monitoring in HCC that can be acquired with low radiation dose. This information is important for further therapy response applications using dual and single energy CT.

Contrast-enhanced computed tomography of the liver, gall bladder and urogenital tract in female red-eared terrapins (Trachemys scripta elegans)

The aim of the present study was to evaluate the feasibility of contrast-enhanced computed tomography for organ morphology and perfusion in five captive terrapins. Native scans were performed and afterwards an iodinated non-ionic contrast media was manually administered through the jugular vein catheter. Post-contrast CT scans were taken 20 (T&lt;sub&gt;20&lt;/sub&gt;), 60 (T&lt;sub&gt;60&lt;/sub&gt;) and 180 (T&lt;sub&gt;180&lt;/sub&gt;) seconds after the contrast medium administration. Maximum contrast enhancement of the kidneys and the liver was detected at T&lt;sub&gt;20&lt;/sub&gt; and T&lt;sub&gt;60&lt;/sub&gt;, respectively. The gall bladder content, the urinary bladder content and ovarian follicles were all without contrast enhancement in all five terrapins. Gall bladder wall thickness was 0.9 mm in all terrapins. Enhancement of the gall bladder wall in post-contrast studies was considered excellent, good or poor in two terrapins, two terrapins and one terrapin, respectively, with a mean score of 1.8 ± 0.84 over all contrast studies. Enhancement of the ureters in post-contrast studies was considered excellent in all terrapins in all contrast studies. Peak aortic enhancement was reached 20 seconds after contrast medium administration with the peak enhancement of 213.5 ± 41 HU in four terrapins and 560 HU in one terrapin. Peak hepatic vein enhancement after contrast medium administration was recorded 20 and 60 seconds in two and three terrapins, respectively. In conclusion, contrast-enhanced computed tomography proved to be a valuable method for clinical examination of the liver, gall bladder, kidneys, ureters, urinary bladder and ovarian follicles in red-eared terrapins.

Optimizing Contrast Media Injection Protocols in Computed Tomography Angiography at Different Tube Voltages: Evaluation in a Circulation Phantom.

The aim of this study was to investigate the minimum iodine delivery rate (IDR) and contrast media (CM) volume required for diagnostic contrast enhancement of 350 HU (Hounsfield units) in the ascending aorta at different kV settings. Dynamic computed tomography acquisitions from 70 to 150 kV were performed in a circulation phantom. First, injections with IDR ranging from 0.1 to 2.0 g I/s were tested for each kV. In the second part, the IDR was held constant, whereas the CM volume was reduced from 50 to 10 mL. Diagnostic aortic peak enhancement for each kV was compared using the Kruskal-Wallis test. P < 0.05 was considered statistically significant. The mean aortic peak enhancement for all diagnostic IDRs was 368.7 ± 11.1 HU. Diagnostic IDRs returned similar aortic peak enhancement values for all protocols (all P ≥ 0.18). For the second part of the study, a diagnostic enhancement was yielded by using a minimum of 30 mL of CM for 110 kV, 25 mL for 100 and 90 kV, and 15 mL for 80 and 70 kV. Our study suggests that a differentiated approach reducing the CM volume for tube voltages of less than 120 kV and increasing the IDR for higher kV settings seems to be the most effective approach.

Optimal injection method for long-range computed tomography angiography.

We aimed to obtain high-stable computed tomography (CT) values for CT angiography (CTA). We verified the optimal use of the new protocol for long-range scanning using a contrast material flow phantom (Ichikawa, CT imaging theory. Igaku syoin Publishing, Tokyo, 8; Awai et al., Am J Roentgenol 186(2):379-385, 1) to obtain high-stable CT values (Fig.2). We have developed a novel contrast injection method called the stable line imaging protocol (SLIP). This method involved a gradual reduction in the rate of administration of the contrast medium, which was accompanied by simultaneous administration of saline to compensate for the resultant decrease in the rate of administration. A saline flush was further added after the contrast medium injection. The rate of administration of the saline flush was the same as that of the initial contrast medium. We injected a contrast medium from the injector into the flow phantom. The time-enhancement curve (TEC) data were obtained five times by changing the injection method, and the average CT values were determined. The maximum simulation of the aortic peak enhancement of TEC was defined as pTEC. The time required to keep the CT value more than 80% of the pTEC was defined as the time period of contrast enhancement (p80). The pTEC of a single injection was 295.7±5.3 HU, while that of SLIP was 296.5±2.3 HU; the two values did not differ significantly. The p80 of a single injection was 19.1±0.2s, while that of SLIP was 23.2±0.4s; p80 of SLIP was 18% longer than that of the single injection.

Peak enhancement ratio of myocardium to aorta for identification of myocardial ischemia using dynamic myocardial computed tomography perfusion imaging

BackgroundThis study aimed to evaluate the feasibility of peak enhancement (PE) ratio of myocardium to aorta (PER) derived from stress dynamic computed tomography myocardial perfusion imaging (CTP) for the detection of myocardial ischemia assessed by magnetic resonance (MR) imaging. MethodsForty-four patients who underwent stress dynamic CTP and MR imaging were retrospectively evaluated. From the time-attenuation curve, myocardial PE, PER, and myocardial blood flow (MBF) were calculated on a segment-based analysis. The correlation between myocardial and aortic PE was assessed by Spearman's correlation, and the differences in myocardial PE and PER between normal and ischemic myocardium were assessed by the Mann–Whitney U-test. The diagnostic accuracies of myocardial PE, PER, and MBF for detecting myocardial ischemia were compared by receiver operating characteristic analysis. ResultsOf 704 segments, 258 segments (37%) were diagnosed as myocardial ischemia with MR imaging. Myocardial and aortic PE were significantly correlated in both normal and ischemic segments (r=0.76 and 0.58; p<0.05, in each). The myocardial PE and PER of ischemic segments were significantly lower than those of normal segments (p<0.05, in each). Sensitivity and specificity were 61% [95% confidence interval (CI), 55–70%] and 83% (95% CI, 73–87%) for myocardial PE, 78% (67–88%) and 82% (95% CI, 70–91%) for PER, and 81% (95% CI, 73–87%) and 85% (95% CI, 79–92%) for MBF. There was a significantly larger area under the curve for PER (0.87; 95% CI, 0.84–0.90) and MBF (0.88; 95%CI, 0.85–0.91), compared to myocardial PE (0.75; 95% CI, 0.70–0.79) (p<0.05, in each). There was no significant difference in area under the curve between PER and MBF. ConclusionsThe semi-quantitative parameter of PER showed a high diagnostic accuracy for the detection of myocardial ischemia, comparable to that of MBF.

Paradoxical Effect of Cardiac Output on Arterial Enhancement at Computed Tomography: Does Cardiac Output Reduction Simply Result in an Increase in Aortic Peak Enhancement?

The aim of this study was to evaluate the effect of cardiac output (CO) on aortic peak enhancement using protocols with different contrast material (CM) injection durations. We used a flow phantom that simulated the human circulatory system. Contrast material was injected at a rate of 4.0 mL/s for a period of 2.5, 5, 10, 15, or 20 seconds for a CO of 2.8, 4.2, and 5.6 L/min. Single-level serial computed tomography scans of the simulated aorta were acquired after the start of CM delivery, and aortic peak enhancement was recorded under the different injection protocols. Under a long injection duration protocol (20 seconds), a decrease in CO increased aortic peak enhancement proportionally (CO of 2.8 L/min, 420 Hounsfield units [HU]; CO of 4.2 L/min, 365 HU; CO of 5.6 L/min, 291 HU). However, this effect was decreased under shorter injection duration protocols (5, 10, and 15 seconds); under the shortest (2.5-second) injection duration protocol, a decrease in CO resulted in a decrease in aortic peak enhancement (CO of 2.8 L/min, 36 HU; CO of 4.2 L/min, 51 HU; CO of 5.6 L/min, 55 HU). The magnitude of the effect of CO on aortic peak enhancement depends on the CM injection duration.

The influence of cardiac function on coronary arterial enhancement at coronary computed tomography angiography: A cross-sectional study.

Background:The purpose of this study was to evaluate the influence of ejection fraction (EF) on peak aortic time (PAT) and peak aortic enhancement (PAE) during coronary computed tomography angiography (CTA).Materials and Methods:One-hundred and twenty patients (64 men, 56 women) underwent measurement of coronary CTA with a measurement of EF within 3 months of coronary CTA. Pearson's correlation coefficient analysis was used to investigate the relationships between EF, PAT and PAE, and peak attenuation of all coronary arteries.Results:The range of EF was (25%–70%) (mean: 55 ± 7.7). The range of PAT and PAE of ascending aorta on bolus test was 13–31 s (mean: 19.3 ± 2) and 153–435 HU (mean: 235 ± 40.6), respectively. Mean peak attenuation of ascending aorta, right coronary artery, left coronary artery, left circumflex artery, and left anterior descending were (561 ± 119), (476 ± 109), (505 ± 108), (467 ± 113), and (473 ± 104), respectively. There was a negative correlation between EF and PAT (r = −0.266, P = 0.003); however, there was no significant correlation between EF and PAE (r = −0.027, P = 0.767). In addition, there was no significant correlation between EF and the peak attenuation of coronary arteries.Conclusion:PAT was related to EF, but there was no relationship between PAE and EF. One of the explanation is that the left ventricular EF used for our study was assessed with echocardiography which is used roughly estimation of EF with interval of 5%–10% and may cause confounding results.

Iodine concentration as a perfusion surrogate marker in oncology: Further elucidation of the underlying mechanisms using Volume Perfusion CT with 80 kVp.

To assess the value of iodine concentration (IC) in computed tomography data acquired with 80kVp, as a surrogate for perfusion imaging in hepatocellular carcinoma (HCC) and lymphoma by comparing iodine related attenuation (IRA) with quantitative Volume Perfusion CT (VPCT)-parameters. VPCT-parameters were compared with intra-tumoral IC at 5 time points after the aortic peak enhancement (APE) with a temporal resolution of 3.5sec in untreated 30 HCC and 30 lymphoma patients. Intra-tumoral perfusion parameters for HCC showed a blood flow (BF) of 52.7 ± 17.0mL/100mL/min, blood volume (BV) 12.6 ± 4.3mL/100mL, arterial liver perfusion (ALP) 44.4 ± 12.8mL/100mL/min. Lesion IC 7sec after APE was 133.4 ± 57.3mg/100mL. Lymphoma showed a BF of 36.8 ± 13.4mL/100mL/min, BV of 8.8 ± 2.8mL/100mL and IC of 118.2 ± 64.5mg/100mL 3.5sec after APE. Strongest correlations exist for VPCT-derived BF and ALP with IC in HCC 7sec after APE (r = 0.71 and r = 0.84) and 3.5sec after APE in lymphoma lesions (r = 0.77). Significant correlations are also present for BV (r = 0.60 and r = 0.65 for HCC and lymphoma, respectively). We identified a good, time-dependent agreement between VPCT-derived flow values and IC in HCC and lymphoma. Thus, CT-derived ICs 7sec after APE in HCC and 3.5sec in lymphoma may be used as surrogate imaging biomarkers for tumor perfusion with 80kVp. • Iodine concentration derived from low kVp CT is regarded as perfusion surrogate • Correlation with Perfusion CT was performed to elucidate timing and histology dependencies • Highest correlation was present 7sec after aortic peak enhancement in hepatocellular carcinoma • In lymphoma, highest correlation was calculated 3.5sec after aortic peak enhancement • With these results, further optimization of Dual energy CT protocols is possible.

Different contrast injection rate on the analysis of 64-slice spiral CT scan liver arterial phase enhancement

Objective To discuss the different contrast injection rate on the 64-slice spiral CT scan liver arterial phase reinforced effect. Methods 60 patients who received abdominal CT scan were selected from January 2014 to April 2015.According to the different conditions, they were divided into control group (30 cases) and liver cirrhosis group (30 cases). Then each group based on packet injection rate into 2.5 mL/s (control group 1, cirrhosis group 1) and 3.5 mL/s (control group 2, cirrhosis group 2). Select Smartprep technology contrast agent tracking all patients, when the abdominal aorta CT value ≥150 HU start scanning.The departure time, CT value of each group were recorded, abdominal aortic artery, simultaneous analysis of each component of image quality comparison. Results When the contrast agent injection rate of 3.5 mL/s, excellent rate of the control group (95.5%) compared with the contrast injection rate of 2.5 mL/s (91.7%) had no significant difference (χ2=0.021, P=0.638); The cirrhosis good rate (94.7%) compared with the contrast agent injection rate of 2.5ml/s (72.7%) had obvious advantages, the difference was statistically significant (χ2=5.233, P=0.032). When the contrast agent injection rate of 2.5mL/s, cirrhosis abdominal aorta average peak enhancement [(187.25±21.00)HU] and the control group [(195.35±19.00)HU] had no significant difference (t=0.826, P=0.436). The average trigger time of the control group (21.68±1.93)s was significantly less than the cirrhosis group (25.13±2.13)s, the difference was statistically significant (t=2.064, P=0.047). When the contrast agent injection rate of 3.5 mL/s, the control group, the mean abdominal aortic peak enhancement [(247.82±39.00)HU] was significantly greater than the cirrhosis group [(223.81±35.00)HU], the difference was statistically significant (t=2.652, P=0.037). The average trigger time of the control group (18.62±1.36)s was significantly less than the cirrhosis group (24.57±0.92)s, the difference was statistically significant (t=3.362, P=0.033). Conclusion The greater the contrast injection rate, arterial peak at the same time it increases the peak time come to shorten.When the contrast agent injection rate consistent with the control group, the average trigger time is short, high average peak enhancement.Cirrhosis needs higher contrast injection rate. Key words: Contrast agent; Cirrhosis; Trigger time; Peak

A new method with variable injection parameters in contrast-enhanced CT: a phantom study for evaluating an aortic peak enhancement.

Contrast-enhanced CT employs a standard uniphasic single-injection method (SIM), wherein administration is based on two parameters: the iodine administration rate (mgI/s) and the injection duration (s). However, as the SIM uses a fixed iodine administration rate, only a uniform contrast enhancement can be achieved with this method. The iodine administration rate can be increased only by increasing the iodine dose or shortening the injection duration, and no arbitrary adjustments can be made to the peak enhancement characteristics of the time-enhancement curves (TECs) at the fixed injection parameters used in the SIM. To address this problem, we developed a variable injection method (VIM) with a new parameter, the variation factor (VF), to adjust the TECs. A phantom study with the VIM indicated that arbitrary adjustments to the iodine administration rate could be made without changing the injection duration or increasing the iodine load. In our study, VFs of 0.3 and 0.5, which showed earlier achievement of peak enhancements, showed better temporal separation between arterial vasculature and parenchyma or the venous vasculature than that obtained with the SIM. The higher peak enhancement provided by the VF of 0.3 was also considered to improve the contrast in qualitative diagnostic examinations. A VF of 0.5 increased the duration of the enhancement and was considered to produce stable enhancement of contrast in vascular investigations. The VF is now an essential parameter, and the VIM is useful as a reasonable contrast method that may contribute to both improved visualization and improvement in the accuracy of morphologic diagnosis.

Intravascular Enhancement With Identical Iodine Delivery Rate Using Different Iodine Contrast Media in a Circulation Phantom

Both iodine delivery rate (IDR) and iodine concentration are decisive factors for vascular enhancement in computed tomographic angiography. It is unclear, however, whether the use of high-iodine concentration contrast media is beneficial to lower iodine concentrations when IDR is kept identical. This study evaluates the effect of using different iodine concentrations on intravascular attenuation in a circulation phantom while maintaining a constant IDR. A circulation phantom with a low-pressure venous compartment and a high-pressure arterial compartment simulating physiological circulation parameters was used (heart rate, 60 beats per minute; stroke volume, 60 mL; blood pressure, 120/80 mm Hg). Maintaining a constant IDR (2.0 g/s) and a constant total iodine load (20 g), prewarmed (37°C) contrast media with differing iodine concentrations (240-400 mg/mL) were injected into the phantom using a double-headed power injector. Serial computed tomographic scans at the level of the ascending aorta (AA), the descending aorta (DA), and the left main coronary artery (LM) were obtained. Total amount of contrast volume (milliliters), iodine delivery (grams of iodine), peak flow rate (milliliter per second), and intravascular pressure (pounds per square inch) were monitored using a dedicated data acquisition program. Attenuation values in the AA, the DA, and the LM were constantly measured (Hounsfield unit [HU]). In addition, time-enhancement curves, aortic peak enhancement, and time to peak were determined. All contrast injection protocols resulted in similar attenuation values: the AA (516 [11] to 531 [37] HU), the DA (514 [17] to 531 [32] HU), and the LM (490 [10] to 507 [17] HU). No significant differences were found between the AA, the DA, and the LM for either peak enhancement (all P > 0.05) or mean time to peak (AA, 19.4 [0.58] to 20.1 [1.05] seconds; DA, 21.1 [1.0] to 21.4 [1.15] seconds; LM, 19.8 [0.58] to 20.1 [1.05] seconds). This phantom study demonstrates that constant injection parameters (IDR, overall iodine load) lead to robust enhancement patterns, regardless of the contrast material used. Higher iodine concentration itself does not lead to higher attenuation levels. These results may stimulate a shift in paradigm toward clinical usage of contrast media with lower iodine concentrations (eg, 240 mg iodine/mL) in individual tailored contrast protocols. The use of low-iodine concentration contrast media is desirable because of the lower viscosity and the resulting lower injection pressure.

Evaluation of Optimal Scan Delay for Gadoxetate Disodium–Enhanced Hepatic Arterial Phase MRI Using MR Fluoroscopic Triggering and Slow Injection Technique

The purpose of this article is to prospectively evaluate the optimal scan delay for gadoxetate disodium-enhanced hepatic arterial phase MRI of hypervascular hepatocellular carcinoma (HCC) using MR fluoroscopic triggering and a slow-injection technique. Sixty-three patients (37 men and 26 women; age range, 33-92 years; mean age, 68.2 years) underwent gadoxetate disodium-enhanced MRI; there were 33 hypervascular HCCs (size range, 8-57 mm; mean size, 19.8 mm) in 19 patients. The time from the start of contrast agent injection to its arrival in the abdominal aorta (time to arrival) and the time from contrast agent arrival to peak enhancement (time to peak) were determined using MR fluoroscopy using IV slow injection at 1 mL/s of contrast material and a saline chaser. All patients underwent four-phase whole-liver imaging with a 3D keyhole gradient-echo sequence during a single breath-hold immediately after confirmation of aortic peak enhancement. Delays from peak aortic enhancement to k-space filling were 5-9, 10-14, 15-19, and 20-28 seconds, respectively, in the four phases. Time to arrival, time to peak, and HCC-to-liver contrast were evaluated. The time to arrival (range, 11-24 seconds; mean, 16.2 seconds) and the time to peak (range, 3-10 seconds; mean, 6.8 seconds) showed considerable variation among patients. HCC-to-liver contrast peaked at the first phase in 58% of cases, at the second phase in 42% of cases, and at the third and fourth phases in 0% of cases. Mean HCC-to-liver contrast in the first and second phases was significantly higher than that in the third and fourth phases (p<0.01). Optimal scan delays for imaging hypervascular HCCs with gadoxetate disodium-enhanced hepatic arterial phase MRI was 7-12 seconds after the peak aortic enhancement using a slow-injection protocol.

Identification of the Iodine Concentration That Yields the Highest Intravascular Enhancement in MDCT Angiography

The objective of our study was to identify the iodine concentration that yields the highest intravascular contrast enhancement in MDCT angiography by intraindividual comparison in an animal model. Six pigs underwent repeated chest MDCT examinations under standardized conditions using the same contrast medium (iopromide) with different iodine concentrations (150, 240, 300, and 370 mg I/mL). The contrast injection protocol was adapted to ensure an identical iodine delivery rate of 1.5 g I/s and the same total iodine dose of 300 mg/kg of body weight for all studies. Dynamic CT scans were acquired at the levels of the pulmonary artery and the ascending and descending aorta. Pulmonary and aortic peak enhancement values as well as time to peak (TTP) were calculated from time-enhancement curves. Pulmonary and aortic peak contrast enhancement values were significantly higher with the 240 and 300 mg I/mL contrast media than the 150 and 370 mg I/mL contrast media (e.g., ascending aorta: 240 vs 150, p = 0.0070; 300 vs 150, p = 0.0096; 240 vs 370, p = 0.0262; 300 vs 370, p = 0.0079). TTP values tended to be lower for the 150 mg I/mL contrast medium than for the contrast media with higher iodine concentrations. Comparison of contrast media with iodine concentrations ranging from 150 to 370 mg I/mL showed that contrast enhancement was significantly improved with the use of 240 and 300 mg I/mL contrast media given a fixed identical iodine delivery and normalized total iodine load in a porcine model. Contrast media with a moderate iodine concentration are most suitable for obtaining the highest intravascular contrast enhancement in CT angiography.

Cardiac Output Obtained from Test Bolus Injections as a Factor in Contrast Injection Rate Revision of Following Coronary CT Angiography

Optimal contrast enhancement is crucial for the detection of coronary artery stenoses and atherosclerotic changes in coronary CT angiography (CTA). To demonstrate the feasibility of using the cardiac output (CO) obtained from the test bolus injection data-set (COtest) as a factor in contrast injection rate revision of the following coronary CTA. The test bolus injection data-sets of 52 consecutive coronary CTAs were examined. COtest was calculated from the test bolus data-set. Aortic peak enhancement (APE) was measured on the following coronary CTA. We simulated the APE at a fixed contrast injection rate of 4 mL/s (simAPE) in each patient. The ranges of COtest and simAPE were 2.82-7.56 L/min and 194-527 Hounsfield Units, respectively. There was a significant negative correlation (R = -0.802, P < 0.001) between simAPE and COtest. COtest can be used for injection rate revision on coronary CTA.

Mo1911 Three-Dimensional Image of Hepatic Hilum by CT Cholangiography With Carbon Dioxide for Preoperative Assessment of Biliary Malignancies

[Background] Curative resection for biliary malignancies involving hepatic hilum is technically-demanding due to complex anatomy of the hepatic hilum. Three-dimensional (3D) presentation of the hepatic hilum structures including bile ducts is supposed to be useful for precise understanding of the anatomy and the tumor extension in individual patients and may improve surgical outcomes. Carbon dioxide (CO2) has been utilized as a radiolucent contrast material. Because CO2 has opposite radiopacity to iodinated contrast material, it may be advantageous to CT cholangiography in which 3D images of bile ducts and vasculatures are simultaneously reconstructed and merged. [Purpose] The purpose of this study is to examine usefulness of CO2 CT cholangiography for preoperative assessment of biliary malignancies. [Patients and Methods] Forty consecutive patients with external biliary drainage (endoscopic nasobiliary drainage (ENBD) or percutaneous transhepatic biliary drainage (PTBD)) who were considered for surgical resection were the subjects of this study. CO2 was injected via biliary drainage tubes so that the bile ducts are filled with CO2 (figure 1). The patients were also given intravenous injection with iodinated contrast media and underwent dynamic CT scan. The arterial and the portal phase images were obtained 5 seconds and 20 seconds after the peak aortic enhancement time, respectively. 3D images were reconstructed for the arteries and the bile ducts from the arterial phase and for the portal vein from the portal phase with 3D analysis software Virtual Place Lexus (AZE, Japan). [Results] Figure 2 shows a representative case with hilar cholangiocarcinoma involving the right hepatic artery and the portal vein. Bile ducts were successfully demonstrated in all cases without occurrence of cholangitis or elevation of liver enzymes. The biliary branches were visualized up to 4.3 rd-order branches on the average. The fusion 3D images of the vasculatures and the bile ducts were useful for recognition of abnormal anatomy or isolated branches, which are often overlooked in conventional two-dimensional cholangiography. Moreover, the synchronous 3D images helped us understand the relative anatomical relationship between the tumor and the surrounding vessels and facilitated precise determination of the cutting line of the bile duct in the operation. Twenty-one patients actually underwent tumor resection and negative surgical margin was achieved in all but two cases with carcinoma in situ at the cutting line. [Conclusion] 3D CT cholangiography with CO2 is a useful tool for preoperative diagnosis, operative planning, and intraoperative navigation of biliary malignancies involving hepatic hilum. Sophisticated operations based on the precise understanding of the anatomy and the tumor extension in individual patients are expected to improve surgical outcomes.

Dynamic CT Angiography after Abdominal Aortic Endovascular Aneurysm Repair: Differences in Contrast Agent Dynamics in the Aorta and Endoleaks—Preliminary Results

PurposeTo assess differences in aortic and endoleak enhancement in patients after endovascular aneurysm repair (EVAR) with dynamic computed tomography (CT) angiography. Materials and MethodsTwenty-one consecutive patients (mean age, 74.5 y ± 6; range, 61–88 y) with endoleaks after EVAR of the abdominal aorta were examined on a second-generation dual-source CT unit with 10 unidirectional scan phases (temporal resolution, 5 s; 80 kV; 120 reference-mAs; z-axis field of view, 283 mm), followed by a venous scan phase. Enhancement was assessed in aorta and endoleaks for all phases by density measurements. The diagnostic reliability of endoleak detection was assessed on a five-point confidence scale. ResultsIn total, 26 endoleaks (type I, n = 1; type II, n = 25) were detected. The highest detection rate was found in phase 5 (22 s after threshold; P < .01 vs other dynamic phases). Mean peak aortic enhancement (560 HU ± 96) was present in an early arterial phase (phase 3, 12 s after threshold), whereas the mean peak endoleak enhancement (398 HU ± 174) for type II endoleaks was present later, in phase 4 (17 s after threshold). Despite perceived high diagnostic confidence in phases 1 and 2 (ie, typical arterial phase of biphasic CT protocol), only 23% and 62% of endoleaks were detected, respectively, whereas peak diagnostic confidence (phases 4 and 5) corresponded well with the maximum endoleak detection rate but decreased significantly in later phases (ie, 6–10). ConclusionsPreliminary dynamic CT angiography results in post-EVAR follow-up revealed notably different peaks of endoleak and aortic enhancement, which are not covered sufficiently by conventional biphasic CT protocols. Phase 5 demonstrated the highest type II endoleak detection rate, with high diagnostic confidence.