Using a saline chaser to decrease contrast media in abdominal CT

Are we systematically overdosing women? Revisiting standardized contrast protocols for thoracoabdominal CT scans

OBJECTIVES

The purpose of this study was to evaluate whether the iodine contrast in blood and solid organs differs between men and women and to evaluate the effect of BMI, height, weight, and blood volume (BV) on sex-specific contrast in staging CT.

MATERIALS AND METHODS

Patients receiving a venous-phase thoracoabdominal Photon-Counting Detector CT (PCD-CT) scan with 100- or 120-mL CM between 08/2021 and 01/2022 were retrospectively included in this single-center study. Image analysis was performed by measuring iodine contrast in the liver, portal vein, spleen, left atrium, left ventricle, pulmonary trunk, ascending and descending aorta on spectral PCD-CT datasets. Univariable and multivariable analyses were performed to assess the impact of sex, age, BMI, height, weight, and BV on the iodine contrast.

RESULTS

A total of 274 patients were included (mean age 68 years ± 12 SD, 168 men). Iodine contrast in organs and blood attenuation was significantly higher in women when using the same volume of CM. Sex, age, BMI, height, weight, and BV significantly influenced iodine contrast. After adjusting for confounding variables, sex remained a significant factor, with women having higher parenchymal and vascular iodine contrast.

CONCLUSION

Standardized or weight-adapted use of CM in venous-phase thoracoabdominal CT scans results in significantly higher contrast in women compared to men. Customizing the CM dose to the patient's BV could result in a similar contrast between sexes. This approach has the potential to reduce the amount of CM, resulting in cost savings, and to decrease the risks associated with CM, particularly for the female sex.

KEY POINTS

Question This study addresses whether current standardized iodinated contrast media protocols lead to systematically higher iodine enhancement in women than in men during thoracoabdominal CT. Findings Women consistently show greater iodine enhancement in blood and abdominal organs compared to BMI-matched men when receiving identical volumes of contrast media. Clinical relevance Adjusting contrast media dosage based on blood volume in venous-phase CT scans could equalize parenchymal and intravascular iodine enhancement across sexes. This approach may reduce unnecessary contrast exposure in women, lower associated risks, and optimize healthcare resource allocation.

Simultaneous Injection of Contrast and Saline Using Spiral Flow-Generating Tube for Hepatic Dynamic Computed Tomography: Effect on Enhancement of Liver Parenchyma and Metastases to the Liver

PURPOSE

Recently, there have been a few reports regarding the usefulness of a novel saline injection technique using a spiral flow-generating tube. The purpose of this study was to evaluate whether simultaneous saline injection using a spiral flow-generating tube was able to improve hepatic contrast enhancement and lesion conspicuity of metastatic liver tumors.

METHODS

We randomized a total of 411 patients with various liver diseases including metastases by total body weight (A, n = 204) and contrast dilution protocol (B, n = 207). Group A received 400 mgI/kg of contrast medium alone without a spiral flow-generating tube; group B received contrast medium 400 mgI/kg simultaneous with injection of a 0.57-ml/kg physiologic saline solution through a spiral flow-generating tube. Abdominal aorta computed tomography (CT) number, hepatic enhancement (ΔHU), percentage of tests demonstrating an enhancement effect of the liver parenchyma exceeding Δ50 HU in 3 measured segments (S2, S6, and S8), and the contrast-to-noise ratio of the metastatic liver tumors were measured.

RESULTS

The mean aortic CT number of group B (417.0 HU ± 61.7; P < 0.01) was approximately 10% higher than that of group A (384.6 ± 79.1 HU). The average ΔHU was 59.8 ± 11.4 HU for group A and 61.7 ± 11.7 for group B. The ΔHU for group B was significantly higher than that for group A ( P = 0.017). The percentage of tests demonstrating with the enhancement effect of group B was more than 80% in all subgroups; however, that of group A was less than 80% in all subgroups. The contrast-to-noise ratio of group B (7.8 ± 3.3 HU) was significantly higher compared to that of group A (6.5 ± 2.8 HU) ( P < 0.05).

CONCLUSIONS

Because of the volume effect, injecting a contrast medium diluted with normal saline improved the degree of hepatic and aortic contrast enhancement and achieved better visualization of liver metastases.

CLINICAL IMPACT

The use of spiral flow-generating tube may help diagnostic of hepatic and aortic contrast enhancement and liver metastases.

IMPORTANCE

The use of a spiral flow-generating tube improved the degree of hepatic and aortic contrast enhancement and achieve better visualization of liver metastases.

POINTS

The use of low-concentration syringe formulations is limited by body weight. However, the use of spiral flow-generating tube provides low-concentration contrast medium regardless of body weight.

Contrast media shortages - medical imaging considerations: A literature review

This literature review was conducted to analyze the current and future effects of intravenous contrast media shortages and how these shortages affect patient care within the field of computed tomography (CT). Substitutions and conservation methods were examined. One of the most important results of this review was to improve current and future patient care while actively making a conscious effort to help aid others in future shortages. Limitations can be found when looking at the research field concerning the substitutions for contrast media, such as nanoparticles and saline chasers following contrast boluses. CINAHL, CINAHL Complete, MEDLINE, MEDLINE Complete, Academic Search Complete, EBSCOhost, and Google Scholar were used to compile articles, which were then eliminated until only those pertaining to this review were left. Thirty-seven articles were included; of the 37 articles, two studied contrast enhancement in animals and were determined relevant to this review. The majority of sources were published within the past 20 years; older articles were included to identify gaps for future research; and all articles selected were peer-reviewed or scholarly. This review indicates the CT field can begin preparations now to help negate future contrast shortages as well as decrease patients' health risks. Future research should revolve around furthering the field's knowledge of nanoparticles being used as ICMs in human patients. Additionally, investigating which ordering providers should have ICM ordering privileges may identify conservation strategies.

Real-time respiratory motion compensated roadmaps for hepatic arterial interventions

PURPOSE

During hepatic arterial interventions, catheter or guidewire position is determined by referencing or overlaying a previously acquired static vessel roadmap. Respiratory motion leads to significant discrepancies between the true position and configuration of the hepatic arteries and the roadmap, which makes navigation and accurate catheter placement more challenging and time consuming. The purpose of this work was to develop a dynamic respiratory motion compensated device guidance system and evaluate the accuracy and real-time performance in an in vivo porcine liver model.

METHODS

The proposed device navigation system estimates a respiratory motion model for the hepatic vasculature from prenavigational X-ray image sequences acquired under free-breathing conditions with and without contrast enhancement. During device navigation, the respiratory state is tracked based on live fluoroscopic images and then used to estimate vessel deformation based on the previously determined motion model. Additionally, guidewires and catheters are segmented from the fluoroscopic images using a deep learning approach. The vessel and device information are combined and shown in a real-time display. Two different display modes are evaluated within this work: (1) a compensated roadmap display, where the vessel roadmap is shown moving with the respiratory motion; (2) an inverse compensated device display, where the device representation is compensated for respiratory motion and overlaid on a static roadmap. A porcine study including seven animals was performed to evaluate the accuracy and real-time performance of the system. In each pig, a guidewire and microcatheter with a radiopaque marker were navigated to distal branches of the hepatic arteries under fluoroscopic guidance. Motion compensated displays were generated showing real-time overlays of the vessel roadmap and intravascular devices. The accuracy of the motion model was estimated by comparing the estimated vessel motion to the motion of the X-ray visible marker.

RESULTS

The median (minimum, maximum) error across animals was 1.08 mm (0.92 mm, 1.87 mm). Across different respiratory states and vessel branch levels, the odds of the guidewire tip being shown in the correct vessel branch were significantly higher (odds ratio = 3.12, p < 0.0001) for motion compensated displays compared to a noncompensated display (median probabilities of 86 and 69%, respectively). The average processing time per frame was 17 ms.

CONCLUSIONS

The proposed respiratory motion compensated device guidance system increased the accuracy of the displayed device position relative to the hepatic vasculature. Additionally, the provided display modes combine both vessel and device information and do not require the mental integration of different displays by the physician. The processing times were well within the range of conventional clinical frame rates.

State of the art of coronary computed tomography angiography

OBJECTIVES

The aim of this paper is to evaluate contrast media (CM) bolus geometry and opacification patterns in the coronary arteries with particular focus on patient, scanner and safety considerations during coronary computed tomography angiography (CCTA).

KEY FINDINGS

The rapid evolution of computed tomography (CT) technology has seen this imaging modality challenge conventional coronary angiography in the evaluation of coronary artery disease. Increases in spatial and temporal resolutions have enabled CCTA to become the modality of choice when evaluating the coronary vascular tree as an alternative in the diagnostic algorithm for acute chest pain. However, these new technologic improvements in scanner technology have imposed new challenges for the optimisation of CM delivery and image acquisition strategies.

CONCLUSION

Understanding basic CM-imaging principles is essential for designing optimal injection protocols according to each specific clinical scenario, independently of scanner technology.

IMPLICATIONS FOR PRACTICE

With rapid advances in CT scanner technology including faster scan acquisitions, the risk of poor opacification of coronary vasculature increases significantly. Therefore, awareness of CM delivery protocols is paramount to consistently provide optimal image quality at a low radiation dose.

Intravenous contrast media in radiation therapy planning computed tomography scans - Current practice in Ireland

Introduction

While Computerised Tomography (CT) remains the gold standard in radiation therapy (RT) planning, inferior soft tissue definition remains a challenge. Intravenous contrast (IVC) use during CT planning can enhance soft tissue contrast optimising Target Volume (TV) and Organ at Risk visualisation and delineation. Despite this known benefit, there are no guidelines for when and how to use IVC in RT planning scans in Ireland.

Aim

The study aims to examine the patterns of practice in relation to the use of IVC in RT planning scans in Ireland and to determine the level of compliance with international guidelines. Radiation Therapists (RTT) IVC training will also be investigated.

Materials and methods

An anonymised online survey was designed based on previously-reported literature. This was distributed to all RT departments in Ireland. The survey contained open, closed and Likert scale questions that investigated IVC practices in each department.

Results

75% (n = 9/12) of Irish departments responded. All responding departments reported using IVC. RTTs cannulated patients in 67% (n = 6/9) of the departments and administration contrast in all departments. Variations from recommended guidelines were found in disease sites where IVC was routinely used and in the assessment of renal functioning prior to contrast administration. IVC training varied in duration and number of supervised procedures required to fulfill competencies.

Conclusion

IVC is used extensively in Irish RT departments. There are variations in IVC practice between departments and with international recommended guidelines.

Usefulness of a saline chaser to reduce contrast material dose in abdominal CT of normal dogs

Use of a saline chaser has been reported to allow reduction of contrast dose and artifacts during computed tomography (CT) examination in humans. This study assesses the extent of contrast dose by using a saline chaser in abdominal CT scans of normal dogs. Five beagles underwent abdominal CT scans. Three protocols were applied: 600 mg I/kg iohexol without saline chaser (protocol 1), 30% lower dose of iohexol (420 mg I/kg) followed by a 10 mL saline chaser (protocol 2), and 40% lower dose of iohexol (360 mg I/kg) followed by a 10 mL saline chaser (protocol 3). Attenuation values were obtained from aorta, portal vein, and liver parenchyma. The maximum enhancement values (MEVs) in protocol 2 were significantly higher than those in protocols 1 and 3 in the aorta; no difference was seen in the portal vein in all protocols. The liver parenchymal MEVs in protocols 1 and 2 were significantly higher than those obtained in protocol 3. In this study, the use of a saline chaser and a reduced dose of contrast material did not affect vessel enhancement. In conclusion, use of a saline chaser for abdominal CT of dogs is recommended because it allows a 30% reduction of contrast dose without decreasing vascular and hepatic parenchymal enhancement.

Comparison of Abdominal Computed Tomographic Enhancement and Organ Lesion Depiction Between Weight-Based Scanner Software Contrast Dosing and a Fixed-Dose Protocol in a Tertiary Care Oncologic Center

OBJECTIVE

This study aimed to evaluate the quality of enhancement and solid-organ lesion depiction using weight-based intravenous (IV) contrast dosing calculated by injector software versus fixed IV contrast dose in oncologic abdominal computed tomographic (CT) examinations.

METHODS

This institutional review board-exempt retrospective cohort study included 134 patients who underwent single-phase abdominal CT before and after implementation of weight-based IV contrast injector software. Patient weight, height, body mass index, and body surface area were determined. Two radiologists qualitatively assessed examinations (4 indicating markedly superior to -4 indicating markedly inferior), and Hounsfield unit measurements were performed.

RESULTS

Enhancement (estimated mean, -0.05; 95% confidence interval [CI], -0.19 to 0.09; P = 0.46) and lesion depiction (estimated mean, -0.01; 95% CI, -0.10 to 0.07; P = 0.79) scores did not differ between CT examinations using weight-based IV contrast versus fixed IV contrast dosing when a minimum of 38.5 g of iodine was used. However, the scores using weight-based IV contrast dosing were lower when the injector software calculated and delivered less than 38.5 g of iodine (estimated mean, -0.81; 95% CI, -1.06 to -0.56; P < 0.0001). There were no significant differences in measured Hounsfield units between the CT examinations using weight-based IV contrast dosing versus fixed IV contrast dosing.

CONCLUSIONS

Oncologic CT image quality was maintained or improved with weight-based IV contrast dosing using injector software when using a minimum amount of 38.5 g of iodine.

LI-RADS technical requirements for CT, MRI, and contrast-enhanced ultrasound

Accurate detection and characterization of liver observations to enable HCC diagnosis and staging using LI-RADS requires a technically adequate imaging exam. To help achieve this objective, LI-RADS has proposed technical requirements for CT, MR, and contrast-enhanced ultrasound of liver. This article reviews the technical requirements for liver imaging, including the description of minimum acceptable technical standards, such as the scanner hardware requirements, recommended dynamic imaging phases, and common technical challenges of liver imaging.

An Individually Optimized Protocol of Contrast Medium Injection in Enhanced CT Scan for Liver Imaging

Objective

To investigate the effectiveness of a new individualized contrast medium injection protocol for enhanced liver CT scan.

Methods

324 patients who underwent plain and dual phase enhanced liver CT were randomly assigned to 2 groups: G1 (n = 224, individualized contrast medium injection protocol); G2 (n = 100, standard contrast medium injection with a dose of 1.5 ml/kg). CT values and ΔHU (CT values difference between plain and enhanced CT) of liver parenchyma and tumor-liver contrast (TLC) during hepatic arterial phase (HAP) and portal venous phase (PVP) and contrast medium dose were measured. The tumor conspicuity of hepatocellular carcinoma (HCC) between two groups was independently evaluated by two radiologists.

Results

The mean contrast medium dose of G1 was statistically lower than that of G2. There were no significantly statistical differences in CT values and ΔHU of liver parenchyma during HAP, TLC values during HAP, and PVP between two groups. The CT values and ΔHU of liver parenchyma during PVP of G2 were significantly higher than those of G1. Two independent radiologists were both in substantial conformity in grading tumor conspicuity.

Conclusion

Using the individually optimized injection protocol might reduce contrast medium dose without impacting on the imaging quality in enhanced liver CT.

Optimization of image quality in pulmonary CT angiography with low dose of contrast material

Aim: The aim of this study was to compare objective image quality data for patient pulmonary embolism between a conventional pulmonary CTA protocol with respect to a novel acquisition protocol performed with optimize radiation dose and less amount of iodinated contrast medium injected to the patients during PE scanning. Materials and Methods: Sixty- four patients with Pulmonary Embolism (PE) possibility, were examined using angio-CT protocol. Patients were randomly assigned to two groups: A (16 women and 16 men, with age ranging from 19-89 years) mean age, 62 years with standard deviation 16; range, 19-89 years) - injected contrast agent: 35-40 ml. B (16 women and 16 men, with age ranging from 28-86 years) - injected contrast agent: 70-80 ml. Other scanning parameters were kept constant. Pulmonary vessel enhancement and image noise were quantified; signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. Subjective vessel contrast was assessed by two radiologists in consensus. Result: A total of 14 cases of PE (22 %) were found in the evaluated of subjects (nine in group A, and five in group B). All PE cases were detected by the two readers. There was no significant difference in the size or location of the PEs between the two groups, the average image noise was 14 HU for group A and 19 HU for group B. The difference was not statistically significant (p = 0.09). Overall, the SNR and CNR were slightly higher on group B (24.4 and 22.5 respectively) compared with group A (19.4 and 16.4 respectively), but those differences were not statistically significant (p = 0.71 and p = 0.35, respectively). Conclusion and Discussion: Both groups that had been evaluated by pulmonary CTA protocol allow similar image quality to be achieved as compared with each other’s, with optimize care dose for both protocol and contrast volume were reduced by 50 % in new protocol comparing to the conventional protocol.

Shaped-bolus protocol reduces contrast medium volume in abdominal CT while maintaining image quality

AIM

To prospectively assess whether bolus shaping to exponentially decrease the contrast medium injection rate leads to alteration in image validity or renal function.

MATERIALS AND METHODS

In this prospective study, patients alternatively received 100 ml contrast medium versus 75 ml via bolus shaping. Image quality was assessed via measurement of attenuation values in the aorta, liver, and spleen and also blinded subjective assessment of image sharpness, low contrast detectability, image noise, and overall quality. Renal function was assessed by change in creatinine levels up to 72 hours post-contrast medium administration.

RESULTS

Of 190 abdominal computed tomography (CT) studies performed in the 3-month period, 98 received the 75 ml dose. There was no significant difference in renal function or objective image quality with a significant improvement in image sharpness in the 100 ml group.

CONCLUSIONS

By using bolus-shaping software, it is possible to maintain objective image quality while reducing the contrast medium load to the patient. This has significant implications regarding clinical practice in decreasing cost and risks associated with iodinated contrast media.

Bariatric CT Imaging: Challenges and Solutions

The obesity epidemic in the adult and pediatric populations affects all aspects of health care, including diagnostic imaging. With the increasing prevalence of obese and morbidly obese patients, bariatric computed tomographic (CT) imaging is becoming common in day-to-day radiology practice, and a basic understanding of the unique problems that bariatric patients pose to the imaging community is crucial in any setting. Because larger patients may not fit into conventional scanners, having a CT scanner with an adequate table load limit, a large gantry aperture, a large scan field of view, and a high-power generator is a prerequisite for bariatric imaging. Iterative reconstruction methods, high tube current, and high tube voltage can reduce the image noise that is frequently seen in bariatric CT images. Truncation artifacts, cropping artifacts, and ring artifacts frequently complicate the interpretation of CT images of larger patients. If recognized, these artifacts can be easily reduced by using the proper CT equipment, scan acquisition parameters, and postprocessing options. Lastly, because of complex contrast material dynamics, contrast material-enhanced studies of bariatric patients require special attention. Understanding how the rate of injection, the scan timing, and the total mass of iodine affect vascular and parenchymal enhancement will help to optimize contrast-enhanced studies in the bariatric population. This article familiarizes the reader with the challenges that are frequently encountered at CT imaging of bariatric patients, beginning with equipment selection and ending with a review of the most commonly encountered obesity-related artifacts and the technical considerations in the acquisition of contrast-enhanced images. (©)RSNA, 2016.

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

Objective

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

Methods

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

Results

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

Conclusions

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

[Assessment of the effects of administering a saline solution flush after contrast medium injection using different injection durations and flush methods]

The purpose of administering a saline solution flush after contrast medium injection is to more effectively utilize the contrast medium remaining in the vessels from the subclavian vein to the superior vena cava. In order to investigate the effects of administering a saline solution flush after a contrast medium injection, we evaluated the effects of various contrast medium injection durations and injection methods on the time-density curve (TDC) using a custom-made TDC measurement phantom. The TDC was found to have a biphasic appearance, showing a rapid increase after the arrival of contrast medium in the target region followed by a slower increase from an inflection point at 25 s after the start of contrast medium injection, reflecting the differences in circulatory dynamics for each duration. The results showed that the effect of saline solution flush was allowed the differences by contrast medium duration at the inflection point. Specifically, when the saline solution flush was administered before the inflection point, the CT number was increased, and when it was administered after the inflection point, contrast enhancement was prolonged. With regard to the method in which the saline solution flush is administered before the inflection point, it was found that injecting a mixture of contrast medium and saline solution before the saline solution flush reduced the degree of inflection of the TDC, resulting in a more stable TDC.

The optimal contrast media policy in CT of the liver. Part I: Technical notes

Latest developments of multidetector computed tomography (MDCT), which is today considered a real volumetric technique, have revolutionized abdominal imaging. Technological improvements such as higher spatial resolution, larger volume coverage and higher temporal resolution, have reduced scan times allowing CT studies of the abdomen within a single breath-hold. Furthermore, the increased number of slices, the submillimetric collimation, and the use of multiple dynamic post-contrast phases per single examination, may all contribute to increase the radiation exposure of single patients. The aim of this review is to discuss different parameters affecting contrast media enhancement, as vascular enhancement, parenchymal enhancement and timing, in order to minimize the amount of contrast medium injected and the radiation exposure.

An optimal contrast dose indicator for the determination of hepatic enhancement in abdominal multidetector computed tomography: comparison of patient attenuation indicator with total body weight and body mass index

PURPOSE

To evaluate a patient attenuation indicator (PAI) as compared with traditional patient-related factors of total body weight and body mass index (BMI) as a predictor of hepatic enhancement in contrast-enhanced abdominal multidetector computed tomography (MDCT).

MATERIALS AND METHODS

Institutional review board approval was obtained, and the study was Health Insurance Portability and Accountability Act compliant. A total of 77 patients (mean age, 53 years; male-female ratio, 32:45) underwent routine contrast-enhanced abdominal CT on a 16-slice multidetector CT (LightSpeed 16; GE Medical Systems, Milwaukee, Wis). Contrast enhancement was achieved by administering a 120-mL iodine contrast medium (350-mg iodine per milliliter) at an injection rate of 3 mL/s followed by an injection of 40-mL saline at 3 mL/s. Computed tomographic attenuation values (Hounsfield units [HU]) of liver parenchyma, main portal vein, and abdominal aorta were measured in each patient. Statistical analysis was performed with linear regression to determine the correlation of PAI, total body weight, and BMI with abdominal organ enhancement.

RESULTS

The mean of PAI, total body weight, and BMI were 28.0 (range, 22.1-34.2), 79.0 kg (range, 49.6-112.2 kg), and 27.5 kg/m (range, 16.8-43 kg/m), respectively. Mean hepatic enhancement was 128.2 HU (range, 73.6-175 HU), mean main portal vein enhancement was 214.2 HU (range, 118-327 HU), and mean abdominal aorta enhancement was 208.9 HU (range, 116-395 HU). Patient attenuation indicator, total body weight, and BMI showed a negative correlation with liver enhancement (r = -0.55, r = -0.4, and r = -0.3, respectively). Patient attenuation indicator exhibited a significantly higher correlation with hepatic enhancement than total body weight and BMI (P < 0.01, respectively).

CONCLUSIONS

Patient attenuation indicator exhibits a moderately inverse correlation with liver enhancement that is greater than those of total body weight and BMI. Patient attenuation indicator may be reliable in predicting the hepatic enhancement degree for a given dose of contrast material and has a potential use in customizing individual patient contrast medium dose during contrast-enhanced abdominal CT.

Use of a saline chaser to reduce the dose of contrast material for dynamic CT in cattle

To investigate the effectiveness of a saline chaser in reducing the required dose of contrast material while carrying out dynamic CT scans in cattle, six clinically normal Holstein calves were subjected to CT scans of the head in a study using a crossover design. The calves were studied as three groups: group A received only contrast material (600 mgI/kg); group B received a 30 per cent lower dose of the same contrast material followed by 50 ml of saline solution; and group C received a 40 per cent lower dose of the same contrast material followed by 50 ml of saline solution. In all the animals, a power injector was used for administering the contrast material, with an injection rate of 4 ml/s and a pressure of 4.7 to 5.7 kg/cm(2). Attenuation values were obtained from the right and left maxillary arteries and dorsal sagittal sinus. There were no significant differences in the maximum enhancement value (MEV) of the maxillary arteries and dorsal sagittal sinus between groups A and B. The MEVs of the maxillary arteries and dorsal sagittal sinus in groups A and B were significantly greater than the MEV in group C (P<0.05). The use of a saline chaser allowed a 30 per cent reduction in the dose of contrast material without decreasing vascular enhancement.

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.

Effect of a saline chaser for contrast enhancement of computed tomographic angiography in cattle

Computed tomographic angiography was performed on nine normal Holstein calves in a crossover method to investigate the effect of a saline chaser for enhancement of the maxillary arteries and dorsal sagittal sinus. One group was administered a contrast injection (600 mg iodine/kg at 4 ml/s) followed by 50 ml of a saline chaser at the same rate as the contrast material. The second group was administered a contrast injection without a saline chaser. Addition of the saline chaser to the contrast material resulted in a higher peak attenuation in the maxillary artery (244.45 +/- 36.19 v 202.20 +/- 27.07, P<0.05) and dorsal sagittal sinus (241.2 +/- 31.51 v 198.88 +/- 21.09, P<0.05). These results indicate that a contrast injection followed by saline chaser increased uptake in contrast-enhanced CT.

Depiction of hypervascular hepatocellular carcinoma with 64-MDCT: comparison of moderate- and high-concentration contrast material with and without saline flush

OBJECTIVE

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.

SUBJECTS AND METHODS

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.

RESULTS

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.

CONCLUSION

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.

[Multislice CT angiography in the study of aneurysm of the abdominal aorta: comparison of three different volumes of contrast agent]

OBJECTIVE

To prospectively and quantitatively compare the use of different volumes of contrast in 16-slice CT angiography for the study of aneurysms of the abdominal aorta before and/or after treatment.

MATERIAL AND METHODS

From November 2005 to March 2006, we included 63 consecutive patients referred for CT angiography for aneurysm of the abdominal aorta or for post-treatment follow-up. Each patient was randomly assigned to one of three groups: group A was administered 100 mL of contrast agent, group B 80 mL, and group C 60 mL. In all cases, contrast was administered with 40 mL of physiological serum at a rate of 4 ml/s. A 16-detector CT scanner was used. In the last 61 patients, attenuation was measured in different locations using circular ROIs. Hounsfield units were recorded in the first slice (initial contrast), in the last slice (final contrast), at their maximum value, and also at one-second intervals.

RESULTS

No statistically significant differences in the Hounsfield units recorded in the first slice, in the last slice, or in the maximum values were found between the different groups. Mean values were above 200 in 58 of 61 patients. Weight and body mass index (BMI) were negatively correlated with aortoiliac attenuation.

CONCLUSION

Using a 16-detector CT scanner enables the volume of contrast for studies of aneurysms of the abdominal aorta to be reduced considerably; however, 60 mL might not be sufficient for patients with high weight or BMI.

Application of PET/CT in the development of novel anticancer drugs

Combined positron emission tomography/computed tomography (PET/CT) is a relatively new imaging modality, combining the functional images of PET with the anatomical information of CT. Since its commercial introduction about 5 years ago, PET/CT has become an important tool in oncology. Currently, the technique is used for primary staging and restaging of cancer patients, as well as for surgery and radiation therapy planning. The abilities of PET/CT to measure early treatment response as well as drug distribution within the body make this technique very useful in the development of novel anticancer drugs. In this paper, the recent literature on the current role of PET/CT in drug development is reviewed.

CTA Contrast Enhancement of the Aorta and Pulmonary Artery

OBJECTIVE

To investigate the effect of saline chase injected at 2 different rates on computed tomography (CT) angiography.

MATERIALS AND METHODS

This study was approved by our institutional animal study committee. Three injection protocols were used; contrast injection (24 mL, 0.8 mL/s) without saline chase (protocol A), contrast injection with saline chase injected at the same rate as the contrast medium (protocol B), and contrast injection with saline chase injected at half the rate (0.4 mL/s) of the contrast medium (protocol C). In the 3 dogs used in our study, each of the protocols was applied twice for every dog resulting in a total of 18 sessions of monitoring scans. CT images were acquired every second at the fixed level of the aorta and pulmonary artery (PA). The duration of plateau, plateau deviation, and peak arterial enhancement were computed and compared using the Kruskall-Wallis and Mann-Whitney U test.

RESULTS

Peak contrast enhancements were significantly more delayed with protocol B than with protocol A in both the PA (B: 48 seconds, A: 30 seconds, P=0.024) and aorta (B: 46 seconds, A: 38 seconds, P=0.024). The duration of enhancement plateau was longer with protocol B than with protocol A in PA (B: 14.8 seconds, A: 9.0 seconds, P=0.002) and in aorta (B: 16.2 seconds, A: 11.6 seconds, P=0.004). Protocol C had the longest duration of plateau in both PA (34.5 seconds, P=0.002) and aorta (33.8 seconds, P=0.004) with uniform plateau enhancement. The peak enhancement values of protocol C, however, were substantially lower than that of protocol A and B in both the PA (A: 262 HU, B: 239 HU, C: 191 HU, P=0.001) and aorta (A: 263 HU, B: 268 HU, C: 210 HU, P=0.001).

CONCLUSIONS

Saline chase prolongs the duration of plateau and delays peak enhancement of the pulmonary artery and aorta. Saline chase injected at half the rate of contrast medium injection allowed more uniform and prolonged plateau contrast enhancement than other protocols.

Determining Contrast Medium Dose and Rate on Basis of Lean Body Weight: Does This Strategy Improve Patient-to-Patient Uniformity of Hepatic Enhancement during Multi–Detector Row CT?

PURPOSE

To prospectively evaluate the use of lean body weight (LBW) as the main determinant of the volume and rate of contrast material administration during multi-detector row computed tomography of the liver.

MATERIALS AND METHODS

This HIPAA-compliant study had institutional review board approval. All patients gave written informed consent. Four protocols were compared. Standard protocol involved 125 mL of iopamidol injected at 4 mL/sec. Total body weight (TBW) protocol involved 0.7 g iodine per kilogram of TBW. Calculated LBW and measured LBW protocols involved 0.86 g of iodine per kilogram and 0.92 g of iodine per kilogram calculated or measured LBW for men and women, respectively. Injection rate used for the three experimental protocols was determined proportionally on the basis of the calculated volume of contrast material. Postcontrast attenuation measurements during portal venous phase were obtained in liver, portal vein, and aorta for each group and were summed for each patient. Patient-to-patient enhancement variability in same group was measured with Levene test. Two-tailed t test was used to compare the three experimental protocols with the standard protocol.

RESULTS

Data analysis was performed in 101 patients (25 or 26 patients per group), including 56 men and 45 women (mean age, 53 years). Average summed attenuation values for standard, TBW, calculated LBW, and measured LBW protocols were 419 HU +/- 50 (standard deviation), 443 HU +/- 51, 433 HU +/- 50, and 426 HU +/- 33, respectively (P = not significant for all). Levene test results for summed attenuation data for standard, TBW, calculated LBW, and measured LBW protocols were 40 +/- 29, 38 +/- 33 (P = .83), 35 +/- 35 (P = .56), and 26 +/- 19 (P = .05), respectively.

CONCLUSION

By excluding highly variable but poorly perfused adipose tissue from calculation of contrast medium dose, the measured LBW protocol may lessen patient-to-patient enhancement variability while maintaining satisfactory hepatic and vascular enhancement.

Usefulness of saline pushing in reduction of contrast material dose in abdominal CT: evaluation of time–density curve for the aorta, portal vein and liver

The effects of saline pushing after contrast material injection were investigated as well as the possibility for this technique to reduce contrast material doses in liver CT examinations. 52 patients were divided randomly into three groups: 100 ml of contrast material (300 mg I ml(-1)) only (A; n = 19), 100 ml of contrast material pushed with 50 ml of saline solution (B; n = 17), and 85 ml of contrast material pushed with 50 ml of saline solution (C; n = 16). Single-level images were obtained at the level of the main portal vein after the initiation of contrast material injection. There were no significant differences in the mean peak enhancement values (PE) and the mean time to peak enhancement values (TPE) of the aorta between the three groups. The mean PE of the portal vein in group B increased 21 HU over that in group A (p<0.05), and there was no significant difference between groups A and C. The mean PE of the liver in group B increased 7 HU over that in group A (p<0.05), and there was no significant difference between groups A and C. The mean TPE of the portal vein was shorter by 4 s (p<0.05), and that of the liver was shorter by 5 s (p<0.05) in group C compared with those in group A. In conclusion, saline pushing increases the enhancement values of the portal vein and liver, and allows a contrast material dose reduction of 15 ml without decreasing hepatic and vascular enhancement at adequate scan timing.

Determination of optimal timing window for pulmonary artery MDCT angiography

OBJECTIVE

The purpose of our study was to determine the optimal timing window for pulmonary artery MDCT angiography.

SUBJECTS AND METHODS

We prospectively studied 150 patients. Routine chest CT scans were acquired using 1.3 mL/kg of contrast medium (370 mg I/mL) that was injected at a fixed injection duration of 30 seconds, followed by a 10-second saline chase. To measure early contrast enhancement, sequential monitoring scans were obtained every 2 seconds over a fixed level of the main pulmonary artery 5 seconds after the start of the injection. Then helical diagnostic scans were obtained at three different predetermined scanning delays (group A, 25 seconds; group B, 35 seconds; and group C, 45 seconds after the start of the injection). Time-enhancement curves; time to reach 100 H, 200 H, and peak enhancement; and enhancement duration greater than 200 H of the pulmonary artery were measured from the monitoring scan. Contrast enhancements of the pulmonary artery and descending aorta and vascular artifacts were assessed from the diagnostic scan.

RESULTS

Times to reach 100 H and 200 H at the pulmonary artery were mean 11 +/- 2.5 (SD) seconds and 16 +/- 3.0 seconds, respectively. Pulmonary artery enhancement duration of greater than 200 H was 25 +/- 2.7 seconds (only obtained in group C). Mean time to peak enhancement (335 +/- 62 H) at the pulmonary artery was 37 seconds. Mean enhancement measured on the diagnostic scan was 294 +/- 43 H, group A; 208 +/- 48 H, group B; and 157 +/- 15 H, group C for the pulmonary artery, and 240 +/- 42 H, group A; 277 +/- 49 H, group B; and 172 +/- 29 H, group C for the aorta (p < 0.01). Artifacts were noted in the superior vena cava (group A, 96.7%; group B, 18.3%; and group C, 0%) and in the subclavian vein (group A, 93.5%; group B, 38.7%; and group C, 0%), (p < 0.05).

CONCLUSION

With our study protocol of a 30-second injection and 10-second saline flush, the optimal temporal window to achieve pulmonary artery enhancement greater than 200 H was from 16 seconds to 41 seconds after the start of the injection.

New acquisition method to exclusively enhance the left side of the heart by a small amount of contrast material achieved by multislice computed tomography with 64 data acquisition system

PURPOSE

To exclusively enhance the left side of the heart by a small amount of contrast material (CM) using rapid acquisition of multislice computed tomography (MSCT) with a 64-data acquisition system (DAS).

MATERIALS AND METHODS

Forty consecutive subjects underwent MSCT (Light Speed VCT, GE) with 0.625mm slice thickness to evaluate coronary arteries. We first measured transit time, using 8ml of CM followed by 20ml saline. Dependent upon transit time, total volume of CM was determined, ranging from 45 to 63ml. After injection of CM at a rate of 4ml/s, followed by 47ml saline at 3.5ml/s, ECG-gated MSCT scanning was performed. The mean and standard deviation (S.D.) of CT values of the right atrium (RA), right ventricle (RV), left atrium (LA), left ventricle (LV), ascending aorta (Ao) and each coronary artery were measured.

RESULTS

The mean of the CT values of the RA, RV, LA, LV, Ao, right coronary artery, left main, left anterior descending branch, and left circumflex branch were 225+/-76, 251+/-72, 353+/-55, 355+/-51, 352+/-34, 312+/-65, 296+/-57, 285+/-55, and 267+/-60HU, respectively. The corresponding S.D.s of the CT values were 39+/-22, 37+/-16, 32+/-7, 31+/-8HU, 25+/-5, 36+/-15, 31+/-13, 36+/-23, and 40+/-18HU, respectively. The mean of CT values of the RA and RV were significantly lower than those of the LA, LV, Ao, and each coronary artery (P<0.01), with excellent S.D.s. We could easily obtain three-dimensional coronary arterial and LV images without artifact of the RA and RV.

CONCLUSIONS

Using 64-DAS MSCT, we successfully obtained exclusive enhancement of the left side of the heart using a small amount of CM.

Utility of triple channel injection of contrast material with mixture of saline, with acquisition in the cephalic direction for arterial trees in the thorax using multislice computed tomography

BACKGROUND

If contrast material is injected into the cubital vein, artifacts due to high concentration of the contrast material in the vein lead to deterioration of the opacification of the thoracic aorta and the major branches. We describe a new protocol employing a combination of triple channel contrast material injection and a mixture of saline with acquisition in the cephalic direction utilizing capability of 16-slice multislice CT.

MATERIALS AND METHODS

Of 35 subjects who underwent thoracic CT, 18 were injected with 70 ml contrast each prior to scanning with acquisition in the cephalic direction during the injection of 30 ml contrast diluted 50/50 with saline, followed by the injection of 20 ml of saline (new protocol). Seventeen subjects were injected each with 100 ml contrast at 3 ml/s, with scanning in the caudal direction (ordinary protocol).

RESULTS

In the new protocol, the major branches of the aorta and the left ventricle were more opacified, but the veins were less opacified compared with the ordinary protocol, resulting in clear delineation of the thoracic aorta and the major branches without artifacts.

CONCLUSIONS

A new acquisition protocol is described in which the thoracic aorta and the major branches can be evaluated without artifact due to high CT values in the veins. Faster, more informative CT scans can be performed using diluted contrast.

Multidetector CT (64 Slices) of the liver: examination techniques

Sixty-four-row MDCT, although developed primarily for cardiac imaging, has the potential to have a great impact on liver imaging as well. Liver-imaging protocols with sub-millimeter collimation improve longitudinal spatial resolution, making the acquired dataset a real isotropic volume perfectly designed for optimal three-dimensional rendering and accurate organ and lesion volumetry. The 64-row detector array offers a wide volumetric coverage (up to 40 mm), suitable not only for shortening scanning time and improving spatial resolution, but also for including a large volume per single rotation, particularly useful for accurate CT perfusion studies. In order to take full benefit from the enormous performance offered by new 64-row MDCT scanners, imaging protocols need to be redesigned. Due to the extremely short scanning window, contrast agent injection should be performed at high flow rate and followed by saline bolus chaser; the use of highly concentrated contrast media might be useful. Timing should be accurately calculated either by a test bolus or, better, by using an automatic bolus-detection technique. Radiation exposure is kept under control, using automatic device-modulating dose delivery according to the patient's anatomy. Finally, the evaluation of acquired volumetric datasets needs the extensive use of a dedicated workstation, with software with sophisticated rendering capabilities.

Multi-detector row CT of the head and neck: comparison of different volumes of contrast material with and without a saline chaser

INTRODUCTION

The aim of this study was to determine the effect of different volumes of contrast material with and without a saline chaser on tissue enhancement in multidetector row CT (MDCT) of the head and neck.

METHODS

In a blind prospective fashion, 120 patients were randomized into the following four groups: group 1, 80 ml contrast material administered at a flow rate of 2.0 ml/s; group 2, 80 ml followed by 40 ml saline at 2.0 ml/s; group 3, 60 ml at 1.5 ml/s; and group 4, 60 ml followed by 30 ml saline at 1.5 ml/s. The attenuation values of the carotid artery, internal jugular vein, and muscle were measured at an interval of 1.5 s in each patient. The degree of perivenous artifacts was subjectively assessed.

RESULTS

Mean attenuation values in the carotid artery and internal jugular vein were significantly higher in groups 1 and 2 than in groups 3 and 4. The width of the diagnostic window (both carotid and jugular enhancement >150 HU) were significantly longer in groups 1 and 2 than in groups 3 and 4. The addition of a saline chaser did not result in improved vascular enhancement or a wider diagnostic window, but reduced perivenous artifacts, compared with using contrast material alone.

CONCLUSION

Reduction of contrast material from 80 to 60 ml results in insufficient enhancement of neck vessels. In addition, the benefit of a saline chaser technique is not obvious except for its ability to reduce perivenous artifacts.

Assessment of the Use of a Saline Chaser to Reduce the Volume of Contrast Medium in Abdominal CT

OBJECTIVE

The purpose of this study was to investigate, first, the effect on enhancement of the liver and aorta during abdominal CT of the use of saline solution as a partial substitute for or in addition to contrast medium when the dose of medium is determined by the patient's body weight and, second, whether use of a saline chaser allows a decrease in the dose of contrast medium to less than 1.5 mL/kg.

SUBJECTS AND METHODS

We enrolled 407 patients undergoing abdominal exploration on MDCT, including an early arterial phase and a portal phase. Group 1 received contrast medium at a dose of 1.5 mL/kg. Group 2 received contrast medium at a dose of 1.5 mL/kg less 20 mL of iodine followed by 30 mL of saline solution. Group 3 received the full 1.5 mL/kg dose of medium followed by a 30-mL saline chaser. Attenuation values were obtained from the aorta in the arterial phase and from the liver in the portal phase.

RESULTS

The groups were comparable in mean body weight and heart rate. None of the differences between them in aortic enhancement in the early arterial phase were statistically significant (group 1, 206 +/- 3 H; group 2, 204 +/- 3 H; group 3, 209 +/- 4 H). There was a negative correlation between weight and aortic enhancement (r = -0.42, p < 0.0001) and a positive correlation between weight and hepatic enhancement (r = 0.19, p < 0.0001). A significant reduction (p = 0.0002) in hepatic enhancement was observed in group 2 (group 1, 53 H; group 2, 46 H; group 3, 54 H). Hepatic enhancement greater than 45 H was observed in all groups except for the group 2 subgroup of patients weighing less than 55 kg.

CONCLUSION

In MDCT, reducing the amount of contrast medium does not affect aortic enhancement in the early arterial phase but decreases hepatic enhancement at the portal phase. The saline chaser technique had no influence on the phases studied. Greater than 1.5 mL/kg reduction in the dose of contrast medium followed by saline flushing may not be advisable for liver CT in low- and medium-weight patients.

Detection and characterization of benign focal liver lesions with multislice CT

MDCT is a rapidly evolving technique that significantly improves CT imaging for several indications including depiction of focal benign lesions. Imaging mainly profits from improved longitudinal spatial resolution allowing high-quality non-axial reformations and 3D reconstructions and CT angiography as well as rapid accurate multiphase imaging with short breath-holding periods. This review provides an overview of the current status of MDCT with respect to liver imaging and the implications for characterizing benign focal liver lesions. MDCT currently allows the acquisition of thin slices in daily routine diagnostics providing an improved detection rate of small liver lesions. Whereas large benign focal liver lesions exhibit typical patterns of morphology, attenuation and perfusion, which also may be assessed with single-slice scanners, small lesions remain challenging even with MDCT, since the specific criteria for confident diagnosis become more ambiguous. Here, MR imaging provides more detailed information about tissue components and the availability of liver-specific contrast agents, adding further impact to this technique. With respect to dose considerations, the number of necessary multiphase scans as well as the application of very thin collimation should be strictly checked for each patient undergoing MDCT based on the individual clinical situation and question.

Effect of saline pushing after contrast material injection in abdominal multidetector computed tomography with the use of different iodine concentrations

PURPOSE

To investigate whether saline pushing after contrast material improves hepatic vascular and parenchymal enhancement, and to determine whether this technique permits decreased contrast material concentration.

MATERIAL AND METHODS

120 patients who underwent hepatic multidetector computed tomography were divided randomly into four groups (Groups A-D): receiving 100 ml of contrast material (300 mgI/ml) only (A) or with 50 ml of saline solution (B); or 100 ml of contrast material (350 mgI/ml) only (C) or with 50 ml of saline solution (D). Computed tomography (CT) values of the aorta in the arterial phase, the portal vein in the portal venous inflow phase, and the liver in the hepatic phase were measured. Visualization of the hepatic artery and the portal vein by 3D CT angiography was evaluated as well.

RESULTS

Although the enhancement values of the aorta were not improved significantly with saline pushing, they continued at a high level to the latter slices with saline pushing. The enhancement value of the portal vein increased significantly and CT portography was improved with saline pushing. The enhancement value of the liver was not improved significantly using saline pushing. In a comparison between groups B and C, the enhancement values of the aorta and portal vein and the visualization of CT arteriography and portography were not statistically different.

CONCLUSION

The saline pushing technique can contribute to a decrease in contrast material concentration for 3D CT arteriography and portography.

Optimal Delay Time for the Hepatic Parenchymal Enhancement at the Multidetector CT Examination

The objective of this study was to determine the optimal scan delay time after hepatic parenchymal enhancement using a 16-channel multidetector row helical CT (MDCT) scanner. Two hundred fifty-five consecutive patients underwent biphasic CT scans using a 16-channel MDCT. In group A (n = 125), two hepatic venous phase scans (HVP1 and HVP2) were obtained at 40 and 60 seconds, after 100-HU threshold time (T100HU) in the abdominal aorta. In group B (n = 130), HVP1 and HVP2 scans were obtained 50 and 70 seconds after T100HU. Both groups were divided into subgroups that were given different contrast media. Groups A1 and B1 received a contrast medium of 300 mgI/mL; groups A2 and B2 received a contrast medium of 370 mgI/mL. Each patient was injected with contrast medium at a dose of 2 mL/kg at a rate adjusted to the patient's body weight with a constant injection duration of 47 seconds. The attenuation values (HU) for the liver, portal vein, hepatic vein, and aorta were measured. The average HU was compared between the groups. Hepatic enhancement in the images obtained at 50 and 60 seconds after T100HU was greater (P < 0.05) than in images obtained at 40 and 70 seconds. These results were obtained with both contrast media. A few patients showed greater enhancement at a 40 seconds or 70 seconds. Hepatic enhancement was significantly greater in all scans using a contrast medium dose of 370 mgI/mL compared with the 300-mgI/mL dose (P < 0.05). Independent of the concentration of contrast medium, scan delays of 50 to 60 seconds after T100HU may provide optimal hepatic enhancement.

Simulation of Aortic Peak Enhancement on MDCT Using a Contrast Material Flow Phantom: Feasibility Study

OBJECTIVE

The objective of our study was to develop a flow phantom simulating aortic peak enhancement after the injection of contrast material on CT and to investigate the validity of the flow phantom by comparing the time-enhancement curves obtained for the flow phantom and humans.

MATERIALS AND METHODS

We developed a flow phantom simulating the enhancement pattern of the aorta after the injection of contrast material. In protocols 1, 2, and 3 of the phantom study, 90, 102, and 150 mL of iohexol, respectively, was administered over 35 sec. In protocol 4, 102 mL of iohexol was administered over 25 sec. In phantom protocols 1', 2', and 3', the dose and contrast injection duration were the same as in protocols 1, 2, and 3; however, saline (10 mL) was injected during the 20 sec after contrast delivery. In the human study, 20 patients were randomized into four groups: Groups A, B, and C received 1.5, 1.7, and 2.5 mL of iohexol per kilogram of body weight, respectively, over 35 sec; and group D received 1.7 mL/kg over 25 sec. In patient groups A, B, C, and D, phantom protocols 1, 2, 3, and 4 were used, respectively. Single-level serial CT scans were obtained using a 16-MDCT scanner on the simulated and real aortas after the injection of contrast material. Time-enhancement curves of simulated and real aortas were generated, and aortic peak times and aortic peak enhancement values were calculated.

RESULTS

Aortic peak enhancement and aortic peak times in protocols 1-4 and 1'-3' of the phantom study were 2-8% larger and 6-18% longer, respectively, than in the corresponding patient study. The shape of the time-enhancement curves before aortic peak time in protocols 1-3 and 1'-3' of the phantom study closely resembled that of the corresponding patient study. After the aortic peak time, the shape of time-enhancement curves in protocols 1, 2, and 3 of the phantom study was different from the corresponding patient study; however, it was similar in phantom protocols 1'-3' and the corresponding patient study. In all four phantom protocols, the difference between maximal and minimal aortic peak enhancement was less than the SD of the corresponding patient study.

CONCLUSION

The level of peak aortic enhancement and the time to peak aortic enhancement were similar in the phantom and human studies when we used our different contrast injection protocols for MDCT.