Aortic Enhancement Research Articles

Improvement of Image Quality of Low Radiation Dose Abdominal CT by Increasing Contrast Enhancement

The purpose of this study was to evaluate the effects of noise index and contrast material dose on radiation dose, contrast enhancement, image noise, and image quality in abdominal CT. Contrast-enhanced abdominal CT with tube current modulation was performed on 195 patients. The patients were prospectively randomized into three groups of equal size (protocol A, noise index of 12 HU and 521 mg I/kg; protocol B, 15 HU and 521 mg I/kg; protocol C, 15 HU and 600 mg I/kg). Scanning was initiated 5 and 45 seconds after aortic enhancement reached 100 HU. Attenuation was measured in the aorta, portal vein, and liver. Transverse CT images were qualitatively graded for diagnostic acceptability and image noise. Arterial phase volume-rendered and multiplanar reformatted (MPR) images and portal venous phase MPR CT angiograms were qualitatively graded for depiction of vessels. Contrast enhancement, objective image noise, radiation dose, and qualitative grades were analyzed and compared among the three groups. The contrast enhancement values of the aorta, portal vein, and liver were higher in protocol C than in protocols A and B (p < 0.05). Objective image noise was greater in protocols B and C than in protocol A (p < 0.05). The radiation dose in protocols B and C was 31-32% lower than in protocol A (p < 0.001). Depiction of vessels, diagnostic acceptability, and subjective image noise were comparable in protocols A and C. Use of higher contrast enhancement can compensate for the degradation of image quality resulting from use of a low radiation dose for CT.

Optimizing scan timing of hepatic arterial phase by physiologic pharmacokinetic analysis in bolus-tracking technique by multi-detector row computed tomography

Our aim in this study was to determine an optimal delay time of hepatic arterial phase (HAP) imaging of hypervascular hepatocellular carcinomas (HCCs) in dynamic contrast-enhanced MDCT (DCE-CT) by use of the bolus-tracking method. The time-enhancement curves (TECs) of the aorta and the contrast of the hepatic arterial and portal system (APC) in the pharmacokinetic analysis were calculated. The clinical study included 41 patients with known or suspected HCC who underwent DCE-CT. The TECs of the aorta and the tumor-liver contrast (TLC) in the clinical study were calculated. On pharmacokinetic analysis, the peak aortic enhancement and the peak APC simulated under conditions of an injection duration of 30 s and an iodine load of 500 mg I/kg body weight were observed 18.5 and 22.5 s, respectively, after the trigger threshold (increased CT value 100 Hounsfield units), respectively. In the clinical study, the peak aortic enhancement and the peak TLC were observed 17.2 and 24.8 s after the trigger threshold, respectively. The optimal delay times until peak aortic enhancement and peak HAP were 15-17 and 19-21 s after the trigger threshold, respectively, under the following conditions: injection dose, 500 mg I/kg body weight; injection duration, 30 s; acquisition time, 5 s; and the trigger threshold. In addition, the peak TLC was achieved 4-7 s after the time to peak aortic enhancement.

Abdominal multi-detector row CT: Effectiveness of determining contrast medium dose on basis of body surface area

To investigate the validity of determining the contrast medium dose based on body surface area (BSA) for the abdominal contrast-enhanced multi-detector row CT comparing with determining based on body weight (BW). Institutional review committee approval was obtained. In this retrospective study, 191 patients those underwent abdominal contrast-enhanced multi-detector row CT were enrolled. All patients received 96 mL of 320 mg I/mL contrast medium at the rate of 3.2 mL. The iodine dose required to enhance 1 HU of the aorta at the arterial phase and that of liver parenchyma at portal venous phase per BSA were calculated (EUBSA) and evaluated the relationship with BSA. Those per BW were also calculated (EUBW) and evaluated. Estimated enhancement values (EEVs) of the aorta and liver parenchyma with two protocols for dose decision based on BSA and BW were calculated and patient-to-patient variability was compared between two protocols using the Levene test. The mean of EUBSA and EUBW were 0.0621 g I/m2/HU and 0.00178 g I/kg/HU for the aorta, and 0.342 g I/m2/HU and 0.00978 g I/kg/HU for the liver parenchyma, respectively. In the aortic enhancement, EUBSA was almost constant regardless of BSA, and the mean absolute deviation of the EEV with the BSA protocol was significantly lower than that with the BW protocol (P<.001), although there was no significant difference between two protocols in the hepatic parenchymal enhancement (P=.92). For the aortic enhancement, determining the contrast medium dose based on BSA was considered to improve patient-to-patient enhancement variability.

Dual-Phase Computed Tomographic Angiography of Focal Nodular Hyperplasia

To test the clinical observation that the postcontrast attenuation level of focal nodular hyperplasia (FNH) at dual-phase computed tomography (CT) rarely exceeds 50% of aortic enhancement or absolute inferior vena cava (IVC) enhancement. Nineteen pathologically proven FNHs in 17 female patients imaged with intravenous contrast-enhanced multidetector CT, of which 15 had arterial and venous phase acquisitions, were evaluated. Two radiologists retrospectively reviewed each CT study in consensus, using axial sections, multiplanar reconstructions, and 3-dimensional rendering techniques (volume rendering and maximum intensity projection). Recorded were precontrast and postcontrast attenuation of mass, the liver, the aorta, and the IVC; lesion size; segmental location; subjective appearance; contour; and presence of central scar, pseudocapsule, septations, feeding artery, or draining vein. The mean FNH attenuation level was lower than 50% of the mean aortic attenuation during the arterial phase (115 vs 144 Hounsfield units) and also lower than the mean IVC attenuation in the portal venous phase (142 vs 153 Hounsfield units). Across cases, the FNH arterial phase attenuation was lower than 50% of the aortic attenuation in 74% (14/19). The portal venous attenuation level of FNH was lower than or equal to that of the IVC in 80% (12/15). One of the 2 enhancement patterns was present in 100% (15/15) of cases. Other common findings included feeding artery and draining vein (18/19), absence of pseudocapsule (18/19), and smooth contour (13/19). A central scar was identified in only 8 of 19 cases, and no lesion contained septations. In this series of patients imaged with contrast-enhanced multidetector CT, most FNHs demonstrated arterial attenuation levels lower than 50% of the aorta and/or portal venous attenuation levels lower than or equal to those of the IVC.

Dual-Energy Computed Tomography Imaging of the Aorta After Endovascular Repair of Abdominal Aortic Aneurysm

Endovascular repair is increasingly considered a less-invasive alternative to open repair of abdominal aortic aneurysm. However, there are still many potential complications of endovascular repair, including endoleaks, graft migration, thrombosis, and fistula formation. Endoleak is the most common complication for which these patients undergo long-term imaging surveillance. Most centers acquire computed tomographic (CT) data before contrast administration and during an arterial and delayed phase of aortic enhancement after the administration of intravenous contrast material to optimize detection of endoleaks. Although this technique works well, the downside is significant patient radiation exposure. Although the carcinogenic risk of ionizing radiation because of CT exposure is low, it has been linked to an increase in the lifelong risk of developing fatal cancers. Furthermore, this risk is cumulative and increases with multiple radiation exposure, as is true in surveillance after endovascular repair. As a result, considerable research is being performed to optimize CT protocols in an effort to decrease radiation dose. One such approach is to image these patients with recently introduced dual source dual-energy CT system. Using this technique, virtual noncontrast data may be generated from a postcontrast acquisition which may obviate the routine acquisition of noncontrast acquisition, thus decreasing radiation dose. In this article, we discuss the role of dual energy CT imaging in evaluation of patients after endovascular repair of abdominal aortic aneurysm.

Contrast Material Injection Protocol With the Dose Adjusted to the Body Surface Area for MDCT Aortography

The objective of our study was to investigate the effect on aortic enhancement of contrast material volumes adjusted for a patient's body surface area (BSA) at CT angiography (CTA). A 64-MDCT scanner was used to perform CTA of the whole aorta in 89 patients (mean age, 68.7 years) with confirmed or suspected aortoiliac disease. The patients were divided into groups: a body weight (BW) group (n = 45) and a BSA (n = 44) group. The contrast dose was 360 mg I/kg BW in the BW group and 12,753 mg I/m(2) BSA in the BSA group. Because the average BW of Japanese adults is approximately 60 kg, the contrast dose in the two protocols was identical in patients weighing 60 kg. We compared aortic enhancement achieved with the two protocols using the two-tailed Student's t test, and we used the generalized linear model to analyze the effect of patient age, sex, and BW on aortic enhancement in each protocol group. The mean aortic enhancement in the BW and BSA groups was 324.2 and 311.7 HU, respectively; the difference was not significant (p = 0.26). In the BW group, BW had a statistically significant effect on aortic enhancement (p < 0.01), whereas neither patient age nor sex did (p = 0.08 and 0.07, respectively). In the BSA group, the age, sex, BW, and BW by sex had no statistically significant effect on aortic enhancement (p = 0.33, 023, 0.10, and 0.16, respectively). Under the BSA protocol, aortic enhancement tended to be consistent and adequate regardless of patient BW.

Contrast Material Administration Protocols for 64-MDCT Angiography: Altering Volume and Rate and Use of a Saline Chaser to Better Match the Imaging Window—Physiologic Phantom Study

The purpose of our study was to evaluate the effect of varying volumes and rates of contrast material, use of a saline chaser, and cardiac output on aortic enhancement characteristics in MDCT angiography (MDCTA) using a physiologic phantom. Volumes of 75, 100, and 125 mL of iopamidol, 370 mg I/mL, were administered at rates of 4, 6, and 8 mL/s. The effect of a saline chaser (50 mL of normal saline, 8 mL/s) was evaluated for each volume and rate combination. Normal, reduced (33% and 50%), and increased (25%) cardiac outputs were simulated. Peak aortic enhancement and duration of peak aortic enhancement were recorded. Analysis of variance models were run with these effects, and the estimated mean levels for the sets of factor combinations were determined. Lowering the volume of contrast material resulted in reduced peak enhancement (example, -56.2 HU [p < 0.0001] with 75 vs 125 mL) and reduced duration of 75% peak enhancement (example, -9.0 seconds [p < 0.0001] with 75 vs 125 mL). Increasing the rate resulted in increased peak enhancement (example, 104.5 HU [p < 0.0001] with a rate of 8 vs 4 mL/s) and decreased duration of 75% peak enhancement (example, -13.0 seconds [p < 0.001]). Use of a saline chaser resulted in increased peak enhancement, and this increase was inversely proportional to contrast material volume. Peak enhancement increased when reduced cardiac output was simulated. Peak enhancement decreased when increased cardiac output was simulated. Reducing contrast material volume from 125 to 75 mL, increasing the rate to 6 or 8 mL/s, and use of a saline chaser result in an aortic enhancement profile that better matches the approximately 5-second imaging window possible with 64-MDCTA of the abdomen and pelvis. Even smaller volumes of contrast material may be adequate in patients with reduced cardiac output.

Depiction of Hypervascular Hepatocellular Carcinoma With 64-MDCT: Comparison of Moderate- and High-Concentration Contrast Material With and Without Saline Flush

The purpose of this study was to evaluate prospectively the depiction of hypervascular hepatocellular carcinoma on 64-MDCT scans obtained with contrast agents of varying iodine concentrations administered with and without saline flush. The study included 149 patients, among whom 36 patients with hypervascular hepatocellular carcinoma were identified. Patients were randomly assigned to one of three protocols: A, contrast material of 300 mg I/mL; B, 370 mg I/mL; C, 370 mg I/mL plus saline flush. In all protocols, the same iodine load per kilogram of body weight (516 mg/kg) was administered for the same injection duration (30 seconds). Enhancement values in the aorta, liver, and portal vein and tumor-liver contrast were measured at multiphase CT. Aortic enhancement was significantly different between protocols A and B (p = 0.04, p < 0.0001) and protocols B and C (p = 0.02, p < 0.001) in the first and second phases. Portal venous enhancement was significantly different between protocols B and C (p = 0.02) in the first phase and between protocols B and C and protocols A and C (p < 0.01, p = 0.02) in the second phase. Tumor-liver contrast was significantly different between protocols A and B (p = 0.03, p = 0.02) and protocols B and C (p = 0.03, p = 0.04) in the first and second phases but not between protocols A and C. There was no significant difference in hepatic enhancement among the three protocols. Use of moderate concentration was more effective than use of a high concentration of contrast material for depiction of hepatocellular carcinoma. Adding a saline flush to the high-concentration protocol eliminated the difference in depiction of hepatocellular carcinoma between the moderate- and high-concentration protocols.

Effect of Contrast Injection Protocols with Dose Adjusted to the Estimated Lean Patient Body Weight on Aortic Enhancement at CT Angiography

The objective of our study was to investigate the effect on aortic enhancement of iodine doses adjusted for the patient estimated lean body weight (LBW) at CT angiography (CTA). CTA for the whole aorta using a 64-MDCT scanner was performed in 97 patients (mean age, 67.4 years) with confirmed or suspected aortoiliac disease. The patients were divided into two groups: a total body weight (TBW) group (n = 49) and an estimated LBW group (n = 48). LBW was estimated from the patient weight (TBW) and height. The TBW and estimated LBW groups received 360 mg I/kg of TBW and 450 mg I/kg of estimated LBW of contrast medium, respectively. The relative dose ratio for the estimated LBW group versus the TBW group was based on the fact that the standard percentage of body fat in Japanese adults with an average TBW of 60 kg is 20% (360 = 0.8 x 450). Differences in the degree of aortic enhancement and interpatient variability in aortic enhancement between the estimated LBW and TBW group were evaluated. Mean aortic enhancement was 308.9 HU for the estimated LBW group and 314.1 HU for the TBW group, indicating no significant difference in the degree of enhancement (Welch's t test, p = 0.61). The interquartile range was smaller for the LBW group than the TBW group (52.8 vs 79.1 HU, respectively); interpatient variability was lower in the estimated LBW group. The aortic attenuation gradient in the TBW group and estimated LBW group was 20.7 and 25.8 HU, respectively; the difference was not statistically significant. The CTA protocol using an estimated LBW-tailored dose yielded more consistent aortic enhancement with reduced interpatient variability than the CTA protocol using a TBW-based dose.

Hepatocellular carcinomas: Correlation between time to peak hepatocellular carcinomas enhancement and time to peak aortic enhancement

Purpose To prospectively assess the relationship between the time to peak enhancement of hepatocellular carcinomas (HCC) and that of the aorta at 64-detector computed tomography (CT). Materials and methods The study prospectively included 43 patients with known HCC. All underwent abdominal CT imaging by using BodyPerfusion CT model. The CT data acquisition was initiated with a delay of 8–15 s from the beginning of the contrast material administered. The time–density curves (TDC) of the HCC and the aorta were drawn. The times to peak enhancement of the HCC and the aorta were recorded and the correlation between the time to peak enhancement of the HCC and that of the aorta was analyzed. Results There were three tendencies of TDC of the HCC enhancement, only 23.3% of them were similar to that of the aorta. The mean time to peak enhancement of the aorta and the HCC (86.1%) was 23.38 s and 30.04 s, respectively. The time to peak enhancement of most HCC was positively and linearly correlated with the time to peak aortic enhancement ( r = 0.662, P < 0.05). Conclusion The result may potentially allow scan delay optimization at contrast material-enhanced CT image in the detection of HCC according to interindividual variability.

Evaluation of required saline volume in dynamic contrast-enhanced computed tomography using saline flush technique

The present study was performed to find the required volume of physiological saline for flushing that will allow the most efficient use of contrast medium during the early phase of dynamic CT. We calculated contrast medium aortic arrival time (AT), time to peak aortic enhancement (TPAE) and the elapsed time to TPAE from AT (rise time) from the TECs of pharmacokinetic analysis and clinical study. The rise time determined in the clinical study was 6.2 s, which was shorter than that in the simulation study. In the present study, an appropriate volume for saline flush was estimated to be about 18 ml.

Abdominal Multidetector CT in Patients with Varying Body Fat Percentages: Estimation of Optimal Contrast Material Dose

To determine if contrast material dose for abdominal multidetector computed tomography (CT), as determined by using body weight (BW), overestimates the amount of contrast material required in heavier patients. Institutional review committee approval and patients' written informed consent were obtained. CT images of the abdomen were obtained by using 2 mL per kilogram of BW of intravenous contrast material (300 mg/mL iodine) injected at 4 mL/sec in 161 consecutive patients (age range, 28-90 years; mean age, 63 years; 95 men, 66 women). CT scans were initiated 45 and 150 seconds after aortic enhancement increased by 50 HU. The patients were divided into low (37-54 kg) and high (55-75 kg) BW groups. The DeltaHU/I, where DeltaHU is change in CT number and I is iodine dose in grams, and adjusted maximum hepatic enhancement (DeltaHU/[I/kg]) were assessed for correlation with BW, body mass index (BMI), and body fat percentage (BFP) by using linear regression. DeltaHU/I correlated (P < .001) inversely with BW in the aorta (r = -0.78) and liver (r = -0.80) and with BMI in the aorta (r = -0.59) and liver (r = -0.61) on portal venous phase images. Regression formula for the low BW group was DeltaHU/I = 4.1 - .044 x BW (P < .001) and for the high BW group was DeltaHU/I = 2.7 - .017 x BW (P < .001), suggesting that the amount of contrast material required with increased BW is less in the high BW group. Adjusted maximum hepatic enhancement directly correlated with BFP (r = 0.25, P < .01). Excessive contrast material may inadvertently be given in heavier patients when the dose is determined by patient BW. Contrast material dose may need to be tailored in individual patients by using BFP.

Introduction of a Dedicated Circulation Phantom for Comprehensive In Vitro Analysis of Intravascular Contrast Material Application

To develop a circulation phantom with physiologic circulation parameters, including a pulmonary and a body circulation for the evaluation of intravascular contrast material (CM) application. The circulation phantom consists of a low-pressure venous system into which CM is injected, a pulmonary circulation, and high-pressure body circulation with an anthropometric aorta and coronary arteries. The phantom is driven by a pulsatile Harvard heart pump. Venous and arterial pressure were set to physiologic values with heart rate (60 beats/min), stroke volume (60 mL), and ratio of diastole to systole (60/40) also were within physiologic limits. CM with different iodine concentrations (300, 370, and 400 mg iodine/mL) were injected at a flow rate of 4 mL/s (iodine delivery rate: 1.2 g, 1.48 g, and 1.6 g iodine/s, respectively; total iodine load for all protocols: 36 g). Serial computed tomography scans at the level of the pulmonary artery, the ascending and the descending aorta replica were obtained. Dynamic pressure in the phantom and true injection system parameters (flow rate, injection pressure, and CM volume) was continuously monitored. Time-enhancement curves were calculated, and pulmonary and aortic peak time and enhancement were determined. Results were compared using nonparametric unpaired Wilcoxon tests. The pressure in the phantom showed physiologic values for the low (mean pressure: 15 mm Hg) and high pressure part (125/75 mm Hg). Programmed injection values (flow rate, pressure, and volume) were reached for all injections. Using CM with 400 mg iodine/mL, the shortest pulmonary and aortic peak times and the highest pulmonary and aortic peak enhancement values were obtained compared with CM with 300 and 370 mg iodine/mL. We developed a flow phantom with physiologic circulation parameters for measurement of contrast enhancement. The phantom is suitable for further evaluation of CM injection protocols for pulmonary and aortic enhancement.

Comparison Between One-Route and Two-Route Injection for Liver and Aortic Enhancement Using MDCT

The purpose of our study was to evaluate whether simultaneous injection into cubital veins bilaterally at one half of the standard injection rate achieves similar hepatic and aortic enhancement on MDCT as the conventional injection rate into a single cubital vein. Thirty-two patients underwent multiphase MDCT because they were suspected of having a hepatic tumor. Patients were assigned to one of the following two groups: group A, 100 mL of 370 mg I/mL of contrast medium injected into a unilateral cubital vein (one-route) via a 20-gauge cannula at a rate of 4 mL/s; or group B, 50 mL of contrast medium injected into the cubital veins bilaterally (two-route) via 24-gauge cannulas at 2 mL/s. Peak contrast enhancement of the liver and abdominal aorta for groups A and B was measured using regions of interest and compared; arrival time of the contrast media was also compared using a bolus-tracking system. Analysis was performed using Wilcoxon's signed rank test. Peak aortic enhancement of groups A and B was 367 +/- 67 H and 361 +/- 113 H (p = 0.61, not significant), respectively, and peak hepatic enhancement of groups A and B was 56 +/- 11 H and 56 +/- 16 H (p = 0.88, not significant), respectively. Mean arrival time to the aorta of group B (19.4 +/- 3.4 seconds) was significantly later compared with that of group A (15.5 +/- 3.5 seconds) (p = 0.005). The slower two-route injection produced the same aortic and hepatic enhancement as the faster one-route method with faster injection, but the arrival time of the contrast medium was later using the two-route method.

Operation of bolus tracking system for prediction of aortic peak enhancement at multidetector row computed tomography: pharmacokinetic analysis and clinical study

The present study was performed to identify the theoretical background for optimal use of the bolus tracking system by analyzing the changes in the initial slope of the aortic time-enhancement curve (TEC). We calculated the contrast medium aortic arrival time (TAR), the time to reach the trigger threshold (effective TAR), the slope of the linear equation of the enhancement unit (enhancement rate), and the time to peak aortic enhancement from the TECs of the pharmacokinetic analysis and retrospective clinical study. In the pharmacokinetic analysis, the enhancement rate-simulated under conditions of injection duration 30 s and iodine load per body weight 500 mg/kg-was 27.1 HU/s. In the clinical study, the enhancement rate was 27.9 +/- 3.0 HU/s. A correlation was found between the TAR and the enhancement rate, indicating that enhancement rates decrease with increasing TAR. It took 22.7 +/- 0.5 s to reach maximum enhancement of the aorta from the trigger threshold of an increase of 100 HU and injection duration at 30 s. We found that cardiac output differences are strongly dependent on the TAR and that most of the differences disappeared during the phase until effective TAR.

Optimal contrast medium injection protocols for the depiction of the Adamkiewicz artery using 64-detector CT angiography

To determine the optimal contrast medium injection protocol for demonstrating the Adamkiewicz artery (AKA) using 64-detector CT angiography (CTA). CTA was performed using 64-detector CT. The study population consisted of 80 patients (mean age 67.2 years) with aortoiliac diseases. In the first 60 patients 540 mg I/kg body weight was administered over 25s. The patients were randomly assigned to three protocols with imaging started at 15 (protocol A-1), 18 (A-2), or 21s (A-3) after triggering (threshold 150 HU). The other 20 received 720 mg I/kg body weight with an imaging delay of 18s (protocol B). Two radiologists evaluated the presence of the AKA and measured the attenuation of the aorta and AKA. Aortic enhancement was 360.4, 348, 279.3, and 372 HU for protocols A-1, A-2, A-3, and B, respectively. There was no significant difference between the A-1 and A-2 protocols (Tukey-Kramer test, p=0.73); however, aortic enhancement was significantly lower in A-3 than A-1 and A-2 (p<0.01). There was no significant difference between A-2 and B (p=0.40). AKA attenuation was 69.3, 91.9, 94.6, and 105.4 HU for protocols A-1, A-2, A-3, and B, respectively. There was no significant difference between the A-2 and A-3 protocols (p=0.91); however, AKA attenuation was significantly lower with A-1 than A-2 or A-3 (p=0.01). AKA attenuation was significantly lower with A-2 than B (p=0.03) and there was a significant difference between A-2 (50%) and B (95%) in the depiction of the hairpin configuration of the AKA (p=0.02). For the demonstration of the AKA at CTA, the optimal protocol used an imaging delay of 18s after triggering and an iodine dose of 720 mg I/kg body weight.

Effect of varying injection rates of a saline chaser on aortic enhancement in CT angiography: phantom study

The effect of varying injection rates of a saline chaser on aortic enhancement in computed tomography (CT) angiography was determined. Single-level, dynamic CT images of a physiological flow phantom were acquired between 0 and 50 s after initiation of contrast medium injection. Four injection protocols were applied with identical contrast medium administration (150 ml injected at 5 ml/s). For baseline protocol A, no saline chaser was applied. For protocols B, C, and D, 50 ml of saline was injected at 2.5 ml/s, 5 ml/s, and 10 ml/s, respectively. Injecting the saline chaser at twice the rate as the contrast medium yielded significantly higher peak aortic enhancement values than injecting the saline at half or at the same rate as the contrast medium (P < 0.05). Average peak aortic enhancement (HU) measured 214, 214, 218, and 226 for protocols A, B, C, and D, respectively. The slower the saline-chaser injection rate, the longer the duration of 90% peak enhancement: 13.6, 12.2, and 11.7 s for protocols B, C, and D, respectively (P > 0.05). In CT angiography, saline chaser injected at twice the rate as the contrast medium leads to increased peak aortic enhancement and saline chaser injected at half the rate tends towards prolonging peak aortic enhancement plateau.

Enhancement Performance of a 64-Slice Triple Rule-Out Protocol vs 16-Slice and 10-Slice Multidetector CT-Angiography Protocols for Evaluation of Aortic and Pulmonary Vasculature

To compare the enhancement of the pulmonary and aortic vasculature between a biphasic injection 64-slice, a single-phase injection 16-slice, and a single-phase injection 10-slice multidetector computed tomographic (CT) angiography (CTA) protocols. With institutional review board approval and Health Insurance Portability and Accountability Act compliance, 50 patients (16 men, 34 women; mean age, 51.5 years; range, 30-75 years) with atypical chest pain from the emergency department were scanned using a triple rule-out protocol on a 64-slice CT scanner. Pulmonary enhancement was compared with 50 patients (21 men, 29 women; mean age, 65.6 years; range, 38-90 years) imaged with a single-phase 16-slice pulmonary angiography protocol. Aortic enhancement was compared with 24 patients (12 men, 12 women; mean age, 66.1; range, 34-92 years) who were imaged with a 16-slice aortic dissection CTA protocol and to 25 patients (15 men, 10 women; mean age, 50.8 years; range, 20-83 years) imaged with a 10-slice aortic dissection CTA protocol. A 2-tailed Student t test or sign test was used to assess significant differences from a vascular attenuation cutoff value of 250 Hounsfield units (HU). Individual mean pulmonary arterial and aortic attenuation values were statistically significantly less than 250 HU for the 16- and 10-slice protocols and statistically significantly more than 250 HU for the 64-slice protocols (P < 0.05). Mean pooled pulmonary attenuation values were more than 250 HU in 18% (9/50) of the 16-slice and in 93% (39/42) of the 64-slice protocols. Mean pooled aortic attenuation values were more than 250 HU in 18.4% (9/49) of the 10- and 16- and in 100% (42/42) of the 64-slice protocols. The triple rule-out 64-slice biphasic injection breath hold CTA protocol provides significantly higher attenuation of aortic and pulmonary vasculature compared with our current 10- and 16-slice protocols.

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

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. 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. 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. 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.

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

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). 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 < or =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. 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. 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.