IV Contrast Selection for MDCT: Current Thoughts and Practice

Lower extremity CT angiography in peripheral arterial disease: from the established approach to evolving technical developments

With the advent of multidetector computed tomography (CT), CT angiography (CTA) has gained widespread popularity for noninvasive imaging of the arterial vasculature. Peripheral extremity CTA can nowadays be performed rapidly with high spatial resolution and a decreased amount of both intravenous contrast and radiation exposure. In patients with peripheral artery disease (PAD), this technique can be used to delineate the bilateral lower extremity arterial tree and to determine the amount of atherosclerotic disease while differentiating between acute and chronic changes. This article provides an overview of several imaging techniques for PAD, specifically discusses the use of peripheral extremity CTA in patients with PAD, clinical indications, established technical considerations and novel technical developments, and the effect of postprocessing imaging techniques and structured reporting.

Feeding Arteries of the Spinal Cord at CT Angiography before and after Thoracic Aortic Endografting

Purpose:

To study the visualization of spinal cord feeding arteries in patients with complex thoracic aortic pathology undergoing endovascular aortic repair (EVAR) using an optimized protocol for multislice computed tomographic angiography (MSCTA).

Methods:

Eighteen consecutive patients (13 men; mean age 63 years, range 45–79) with aortic type B dissections (n=5), chronic expanding aortic dissections (n=5), thoracic aortic aneurysms (n=6), or penetrating aortic ulcers (n=2) underwent 16-slice CTA before and after (mean interval 9 days) EVAR. Pulse rate and neurological status were documented. Quantitative density measurements were taken at regions of interest (ROI) in the ascending thoracic aorta and at the level of the diaphragm. Two experienced radiologists qualitatively assessed the posterior intercostal arteries (PIA; fully visible, partially visible, non-visible), dorsal branches (DB; visible/non-visible), and artery of Adamkiewicz (AKA; visible/non-visible) on multiplanar reformations and maximum intensity projection reconstructions.

Results:

MSCTA was performed successfully in 17/18 patients before and after EVAR (1 patient was excluded after EVAR owing to rising creatinine levels). Before EVAR, MSCTA revealed 197/203 PIAs within the stented area, of which 179 were fully and 18 partially visible. No significant (p=0.37) difference was noted for overall PIA detection within the stented area on post-EVAR MSCTA (185/203 PIA), although only 124 were fully and 61 partially visible. Similar results were obtained for DB visualization. The AKA were seen in 10/17 patients pre EVAR and 9/17 post EVAR. In 2 patients, the AKA was localized within the stented aortic segment. ROI analysis revealed contrast densities of 427±89 HU and 398±84 HU on pre- and post-EVAR MSCTA, respectively. No neurological events were observed.

Conclusion:

The majority of posterior intercostal arteries and dorsal branches remain open after EVAR due to retrograde perfusion. High-resolution MSCTA permits accurate pre-and post-EVAR visualization of spinal cord feeding arteries in patients with thoracic aortic pathology.

Unstable abdominal aortic aneurysms: a review of MDCT imaging features

Abdominal aortic aneurysms are commonly encountered during abdominal CT imaging, and size-based parameters for surgical or endovascular repair are well established. Aneurysms greater than 5 cm in diameter are recognized as representing an increased rupture risk and meriting intervention. Increasingly, additional interest has been generated in recognizing imaging features which may herald instability and portend a higher chance for potentially catastrophic rupture. This article will review and illustrate such signs, including hyperattenuation of mural thrombus, rapid expansion, low thrombus to lumen ratio, intimal calcification disruption, posterior mural draping, and saccular outpouching. Other features of complicated abdominal aneurysms including perianeurysmal inflammation, aortocaval and aortoenteric fistula formation will also be addressed. Heightened awareness of these features and their prognostic implications, as well as timely communication with the clinical service, is critical for the interpreting radiologist.

Abdominal aortic aneurysms revisited: MDCT with multiplanar reconstructions for identifying indicators of instability in the pre- and postoperative patient

Rupture of an abdominal aortic aneurysm is commonly a fatal event. Multidetector computed tomographic (CT) signs of frank aortic rupture are usually readily apparent and widely understood. However, diagnosing an impending aortic rupture on the basis of imaging findings can prove more difficult. CT is the primary modality used for serial imaging in patients with aortic aneurysm and may show findings indicative of aortic instability. Therefore, it is critical that radiologists be familiar with the CT findings of aortic instability to avert the potential complications of hemorrhage, end organ or limb ischemia, and death. Various preoperative CT indicators have been previously described in both research investigations and review articles. A large baseline aneurysm size and a rapid increase in size over time are associated with a higher risk for rupture. The importance of obtaining accurate measurements with multiplanar reconstructions and the role of new semiautomated tools for obtaining accurate, reproducible measurements are discussed. Additional CT findings that reflect aortic aneurysm instability include luminal expansion with lysis of thrombus, intramural hemorrhage (ie, the crescent sign), periaortic hemorrhage, a penetrating atherosclerotic ulcer, and contained rupture (ie, the draped aorta sign). After open or endovascular aneurysm repair, CT is routinely used to monitor for graft complications. In this setting, radiologists should understand that the presence of an endoluminal stent or surgical graft does not preclude aortic rupture. Online supplemental material is available for this article.

Defining vascular signatures of benign hepatic masses: role of MDCT with 3D rendering

Multidetector CT (MDCT) provides new opportunities for hepatic tumor characterization. By coupling high-resolution isotropic datasets with advanced post-processing tools, maps of tumor vascularity can be generated to elucidate characteristic findings. This two-part review describes a range of benign and malignant liver masses, with emphasis on IV contrast-enhanced MDCT features and vascular signatures that can be identified on 3D vascular mapping.

CT angiography of intracranial arterial vessels: impact of tube voltage and contrast media concentration on image quality

BACKGROUND

Computed tomography angiography (CTA) of intracranial arteries has high demands on image quality. Important parameters influencing vessel enhancement are injection rate, concentration of contrast media and tube voltage.

PURPOSE

To evaluate the impact of an increase of contrast media concentration from 300 to 400 mg iodine/mL (mgI/mL) and the effect of a decrease of tube voltage from 120 to 90 kVp on vessel attenuation and image quality in CT angiography of intracranial arteries.

MATERIAL AND METHODS

Sixty-three patients were included into three protocol groups: Group I, 300 mgI/mL 120 kVp; Group II, 400 mgI/mL 120 kVp; Group III, 400 mgI/mL 90 kVp. Hounsfield units (HU) were measured in the internal carotid artery (ICA) and the M1 and M2 segments of the middle cerebral artery. Image quality grading was performed regarding M1 and M2 segments, volume rendering and general image impression.

RESULTS

The difference in mean HU in ICA concerning the effect of contrast media concentration was statistically significant (P = 0.03) in favor of higher concentration. The difference in ICA enhancement due to the effect of tube voltage was statistically significant (P < 0.01) in favor of lower tube voltage. The increase of contrast medium concentration raised the mean enhancement in ICA with 18% and the decrease of tube voltage raised the mean enhancement with 37%. Image quality grading showed a trend towards improved grading for higher contrast concentration and lower tube voltage. Statistically significant better grading was found for the combined effect of both measures except for general impression (P 0.01-0.05).

CONCLUSION

The uses of highly concentrated contrast media and low tube voltage are easily performed measures to improve image quality in CTA of intracranial vessel.

Accuracy of hepatocellular carcinoma detection on multidetector CT in a transplant liver population with explant liver correlation

AIM

To evaluate the diagnostic accuracy of multidetector computed tomography (MDCT) for hepatocellular carcinoma (HCC) in cirrhotic patients undergoing liver transplantation. Secondary aims were to examine the effect of radiologist experience and lesion size on diagnostic accuracy.

MATERIALS AND METHODS

Thirty-nine patients (72% male with a mean age of 56.5 years) underwent liver transplantation following preoperative triple-phase MDCT examination of the liver. MDCT examinations were retrospectively independently reviewed by three radiologists for the presence and location of suspected HCCs, with the diagnostic confidence recorded using a five-point confidence scale. MDCT examinations were compared with explant specimens for histopathological correlation.

RESULTS

Histopathological results demonstrated 46 HCCs in 29 of the 39 patients. Analysis demonstrated a sensitivity of 65-75% and specificity of 47-88% for detection of HCC lesions. The sensitivity dropped to 48-57% for lesions of size ≤20mm. As the diagnostic confidence increased, there was a further decrease in the sensitivity (4-26%). The radiologist with the greatest number of years experience was found to have a significantly higher accuracy of detection of HCC lesions compared with the least experienced radiologist.

CONCLUSION

Larger lesion size of HCC and greater number of years experience of the radiologist resulted in significantly higher accuracy of HCC lesion detection. The overall sensitivity and specificity results for MDCT detection of HCC are comparable to previous helical CT imaging.

Technical considerations for lower limb multidetector computed tomographic angiography

Multidetector computed tomography (MDCT) enables imaging of the entire arterial tree non-invasively. Optimal technical considerations for performing MDCT angiography (MDCTA) are essential for accurate diagnosis and atherosclerotic disease stratification. This review article focuses on the various technical aspects necessary for peripheral computed tomographic angiography (CTA) acquisition. Common clinical indications for peripheral MDCTA and the latest scan protocols are described. The essential issue of radiation dose reduction is discussed, along with methods of optimal contrast bolus detection and delivery. Post-processing techniques are also presented. Previously, digital subtraction angiography was the only established reliable imaging technique to quantify atherosclerotic disease load; however, MDCTA may now challenge this old gold standard, along with other non-invasive techniques such as magnetic resonance angiography (MRA).

Secretin-stimulated multi-detector CT versus mangafodipir trisodium-enhanced MR imaging plus MRCP in characterization of non-metastatic solid pancreatic lesions

BACKGROUND AND AIM

Our study was aimed to compare multiphasic multi-detector computed tomography after secretin stimulation and mangafodipir trisodium-enhanced magnetic resonance imaging plus MR cholangiopancreatography in the characterization of solid pancreatic lesions.

PATIENTS AND METHODS

Forty patients with ultrasound diagnosis of solid pancreatic lesion prospectively underwent both multi-detector computed tomography and magnetic resonance imaging. Three minutes after intravenous administration of secretin, post-contrast computed tomography scans were performed 40, 80, and 180 s after contrast medium injection. MR protocol included axial/coronal, thin/thick-slab, single-shot T2 w sequences and axial/coronal T1 w breath-hold spoiled gradient-echo images before and 30-40 min after intravenous infusion of manganese dipyri-doxal diphosphate. Different observers blindly evaluated the ability of computed tomography and magnetic resonance imaging to characterize focal pancreatic lesions. Surgery, biopsy, and/or follow-up were considered as our diagnostic gold standard.

RESULTS

Thirty-five focal pancreatic lesions (adenocarcinoma, n=18; focal chronic pancreatitis, n=4; endocrine tumor, n=6; metastasis, n=1; cystic tumor, n=3; indeterminate cystic lesions, n=3) were present in 34 patients since the remaining 6 subjects showed no pathological finding. Both multi-detector computed tomography and magnetic resonance imaging showed a statistically significant correlation with the gold standard and between themselves in the characterization of 29 solid lesions of the pancreas (p<0.05).

CONCLUSION

Both imaging techniques well correlate to final diagnosis of non-metastatic solid pancreatic lesions and particularly of adenocarcinomas with a slight advantage for mangafodipir trisodium-enhanced magnetic resonance imaging plus MR cholangiopancreatography.

64-Slice CT angiography of the abdominal aorta and abdominal arteries: comparison of the diagnostic efficacy of iobitridol 350 mgI/ml versus iomeprol 400 mgI/ml in a prospective, randomised, double-blind multi-centre trial

Purpose

The purpose of this study was to assess the influence of iodine concentration on diagnostic efficacy in multi-detector-row computed tomography (MDCT) angiography of the abdominal aorta and abdominal arteries.

Methods

IRB approval and informed consent were obtained. In this double-blind trial, patients were randomised to undergo MDCT angiography of the abdominal arteries during administration of iobitridol (350 mgI/ml) or iomeprol (400 mgI/ml). Each centre applied its own technique for delivery of contrast medium, regardless of iodine concentration. Diagnostic efficacy, image quality, visualisation of the arterial wall and arterial enhancement were evaluated. A total of 153 patients received iobitridol and 154 received iomeprol.

Results

The ability to reach a diagnosis was “satisfactory” to “totally satisfactory” in 152 (99.3%) and 153 (99.4%) patients respectively. Image quality was rated as being “good” to “excellent” in 94.7 and 94.8% segments respectively. Similar results were observed for image quality of arterial walls (84.3 vs. 83.2%). The mean relative changes in arterial enhancement between baseline and arterial phase images showed no statistically significant differences.

Conclusion

This study demonstrated the non-inferiority of the 350 versus 400 mgI/ml iodine concentration, in terms of diagnostic efficacy, in abdominal MDCT angiography. It also confirmed the high robustness and reliability of this technique across multi-national practices.

Comparison between 64-row CT angiography and digital subtraction angiography in the study of lower extremities: personal experience

PURPOSE

This study was undertaken to evaluate the potential of 64-row multislice computed tomography (CT) versus digital subtraction angiography (DSA) in detecting significant lesions of lower-extremity inflow and runoff arteries.

MATERIALS AND METHODS

Fifty-three patients underwent 64-row multislice CT and DSA over a mean of 36 days. The vascular tree was divided into 33 segments. Three readers independently reviewed the axial CT scans and multiplanar oblique and two- and three-dimensional reconstructions (maximum intensity projection and volume rendering) images to assess degree of stenosis according to four categories: 1 (0%-49% stenosis); 2 (50%-99% stenosis); 3 (occluded); 4 (not evaluable). In all cases, DSA was performed by arterial catheterisation.

RESULTS

In 53 patients, 1,440 segments were evaluated (infrarenal aorta and 16 arterial segments for each leg; 42 bilateral studies, 11 unilateral studies). Compared with DSA, CT angiography yielded 97.2% sensitivity, 97% specificity, 92.5% positive predictive value, 98.9% negative predictive value, 97.1% diagnostic accuracy and 95.4% concordance on the degree of stenosis.

CONCLUSIONS

Sixty-four-row multislice CT proved to be helpful in detecting haemodynamically significant lesions in peripheral arterial occlusive disease and improved the results obtained with 4- and 16-slice multidetector CT. In addition, owing to the high spatial resolution and rigorous technique, no variations in the data obtained below the knee were detected, overcoming a limitation of earlier generations of CT scanners.

Effect of X-ray tube parameters, iodine concentration, and patient size on image quality in pulmonary computed tomography angiography: a chest-phantom-study

OBJECTIVES

The aim of this phantom study was to evaluate the contrast-to-noise ratio (CNR) in pulmonary computed tomography (CT)-angiography for 300 and 400 mg iodine/mL contrast media using variable x-ray tube parameters and patient sizes. We also analyzed the possible strategies of dose reduction in patients with different sizes.

MATERIALS AND METHODS

The segmental pulmonary arteries were simulated by plastic tubes filled with 1:30 diluted solutions of 300 and 400 mg iodine/mL contrast media in a chest phantom mimicking thick, intermediate, and thin patients. Volume scanning was done with a CT scanner at 80, 100, 120, and 140 kVp. Tube current-time products (mAs) varied between 50 and 120% of the optimal value given by the built-in automatic dose optimization protocol. Attenuation values and CNR for both contrast media were evaluated and compared with the volume CT dose index (CTDI(vol)). Figure of merit, calculated as CNR/CTDIvol, was used to quantify image quality improvement per exposure risk to the patient.

RESULTS

Attenuation of iodinated contrast media increased both with decreasing tube voltage and patient size. A CTDIvol reduction by 44% was achieved in the thin phantom with the use of 80 instead of 140 kVp without deterioration of CNR. Figure of merit correlated with kVp in the thin phantom (r = -0.897 to -0.999; P < 0.05) but not in the intermediate and thick phantoms (P = 0.09-0.71), reflecting a decreasing benefit of tube voltage reduction on image quality as the thickness of the phantom increased. Compared with the 300 mg iodine/mL concentration, the same CNR for 400 mg iodine/mL contrast medium was achieved at a lower CTDIvol by 18 to 40%, depending on phantom size and applied tube voltage.

CONCLUSIONS

Low kVp protocols for pulmonary embolism are potentially advantageous especially in thin and, to a lesser extent, in intermediate patients. Thin patients profit from low voltage protocols preserving a good CNR at a lower exposure. The use of 80 kVp in obese patients may be problematic because of the limitation of the tube current available, reduced CNR, and high skin dose. The high CNR of the 400 mg iodine/mL contrast medium together with lower tube energy and/or current can be used for exposure reduction.

Preoperative imaging for metastasectomy

For most solid neoplasms, medical imaging is a vital component of tumor staging and surveillance. Imaging strategies vary according to the type and grade of primary neoplasm, tumor stage at diagnosis, tumor markers, previous therapies, and patient symptoms. In this article, we address imaging of individual organs (lung, liver, adrenals) and outline imaging strategies for specific types of neoplasms.

Pancreatic adenocarcinoma: analysis of the effect of various concentrations of contrast material

PURPOSE

The aim of this study was to compare the efficacy of two contrast materials with moderate and high iodine concentrations for the depiction of pancreatic adenocarcinoma.

MATERIALS AND METHODS

A series of 107 patients with histologically proven pancreatic adenocarcinoma underwent helical computed tomography. A fixed dose of 100 ml of iopamidol 300 (mg I/ml) was administered to 50 patients (group A) and iopamidol 370 (mg I/ml) to 57 patients (group B) at the same injection rate (3 ml/s). Unenhanced helical scans and contrast-enhanced scans for three phases (30, 70, and 300 s after starting the infusion of contrast material) were obtained. We evaluated enhancement of the aorta, portal vein, hepatic parenchyma, pancreatic parenchyma, and pancreatic adenocarcinoma during each phase.

RESULTS

During all phases, both aortic and pancreatic enhancement were significantly greater in group B than in group A (P<0.01). Enhancement of the portal vein and hepatic parenchyma was significantly greater at 70 and 300 s in group B than in group A (both P<0.01). Tumor-to-pancreas contrast was significantly greater in group B than in group A at both 30 s (P<0.01) and 70 s (P<0.05).

CONCLUSION

Administration of contrast material with a high iodine concentration is more effective for depicting pancreatic adenocarcinomas.

[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.