Value of image subtraction in 3D gadolinium-enhanced MR angiography of the renal arteries

The objective of this study was to evaluate quantitatively and qualitatively the effect of image subtraction on the image quality of three-dimensional (3D) gadolinium-enhanced MR angiograms of the renal arteries. Breath-hold 3D gadolinium MR angiography (MRA) as well as conventional contrast angiography of the renal arteries was performed on 20 patients with suspected renovascular hypertension. MR angiograms were acquired before and during dynamic infusion of gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA). Contrast-enhanced images were compared with images that had undergone voxel-by-voxel signal intensity subtraction of contrast-enhanced data from precontrast data. One false positive finding for significant renal artery stenosis was recorded with MRA using conventional angiography as the gold standard. Image subtraction did not alter the diagnosis at MRA in any case. The mean contrast-to-noise ratio (CNR) was significantly higher (P < .05) on the subtraction MR angiograms compared to the nonsubtracted MR angiograms. There was no significant difference in the signal-to-noise ratio (SNR). Qualitative analysis revealed a significant improvement in image quality after image subtraction with respect to visualization of the distal renal arteries. In conclusion, image subtraction improves the quality of renal MRA in terms of both CNR and visualization of the distal renal arteries.     

Effect of gadolinium on phase-contrast MR angiography of the renal arteries

OBJECTIVE: Our aim was to evaluate the effect of gadolinium chelates on image quality in phase-contrast MR angiography of renal arteries in patients suspected of having renal artery stenosis. MATERIALS AND METHODS: In 24 patients, axial three-dimensional phase-contrast MR angiography of the renal arteries was obtained on a 1.5-T MR imaging system before and after administration of gadolinium contrast agent. The improvement in distal renal artery signal-to-noise ratio after enhancement was measured and correlated with patient age, serum creatinine level, clinical estimation of renal artery flow, and the imaging parameter flip angle. RESULTS: On average, the distal renal artery signal-to-noise ratio increased 2.2-fold after gadolinium administration (p < .001). The increase was greatest in patients more than 60 years old (3.1-fold; p < .001) and in patients with serum creatinine levels greater than 3.0 mg/dl (4.3-fold; p < .01). After enhancement, we found an apparent increase in renal artery diameter (3.5 +/- 1.1 mm before enhancement versus 4.8 +/- 1.4 mm after enhancement [mean +/- SD; p < .001]). We believe this increase reflects improved visualization of slow blood flow along the artery wall. Although the visualization of renal arteries was better in most patients after enhancement, two patients had poorer image quality after enhancement because of increased venous signal obscuring the arteries. CONCLUSION: Gadolinium administration significantly increases distal renal artery signal-to-noise ratio on three-dimensional phase-contrast MR angiography in most patients. The signal-to-noise ratio improvement is greatest in older patients and in patients with impaired renal function. However, in some cases, increased venous signal may obscure arteries.     

The identity of the previous visitor influences flower rejection by nectar-collecting bees

PURPOSE: To compare subtracted and nonsubtracted gadolinium-enhanced magnetic resonance (MR) angiography and cardiac-synchronized time-of-flight MR angiography for help in detecting pelvic-region stenoses. MATERIALS AND METHODS: Twenty-eight patients with intermittent claudication underwent MR angiography with a 1.5-T system; two-dimensional cardiac-synchronized time-of-flight MR angiograms and three-dimensional MR angiograms (without and with gadolinium enhancement) were obtained. Subtracted images were obtained by subtracting unenhanced data from enhanced data of identical volumes, and maximum intensity projection images were constructed, which two observers independently evaluated in blinded fashion, with conventional angiographic results as the reference standard. RESULTS: Sensitivity and specificity for grading of hemodynamically significant stenoses (> or = 50% lumen reduction) on subtracted MR angiograms were 94% and 93%, respectively. Sensitivity of subtracted images was significantly higher compared with that of time-of-flight images (P < .05) but not with that of nonsubtracted images. Contrast-to-noise ratio on subtracted images was significantly higher compared with that on nonsubtracted images (P < .05) but not with that on time-of-flight images. There was good correlation between stenosis length measurements on gadolinium-enhanced MR angiograms and those on conventional angiograms. CONCLUSION: Subtracted MR angiography is superior to cardiac-synchronized time-of-flight MR angiography for imaging of iliac and upper femoral arteries and provides higher contrast-to-noise ratio, fewer artifacts, and easier image interpretability than nonsubtracted MR angiography.     

Breath-hold gadolinium-enhanced MR angiography of the major vessels at 1.0 T: dose-response findings and angiographic correlation

PURPOSE: To find the appropriate contrast agent dose for gadolinium-enhanced magnetic resonance (MR) angiography by using individual measurement of contrast agent transit times in a randomized study. MATERIALS AND METHODS: A total of 34 patients with disease of the aorta or its major branches or both were randomly assigned to receive a dose of 0.1, 0.2, or 0.3 mmol of gadopentetate dimeglumine per kilogram of body weight. Initially, contrast agent transit times were measured with use of a turbo fast-low-angle-shot sequence. Subsequently, a three-dimensional fast imaging with steady-state precession sequence (7.3-msec repetition time, 2.8-msec echo time) was used for breath-hold MR angiography. Gadopentetate dimeglumine was injected with an MR-compatible power injector. Efficacy was evaluated by measurement of vessel enhancement and by clinical correlation of MR angiograms with x-ray angiograms. RESULTS: Evaluation of contrast agent transit time was possible in all patients with the test doses, which provided contrast-enhanced MR angiograms of constant quality. Neither vessel enhancement nor diagnostic information was significantly different across the these study groups. CONCLUSION: The clinical gadolinium dose of 0.1 mmol/kg is sufficient for diagnostic assessment of the aorta and its major branches at contrast-enhanced MR angiography. High-dose studies appear not to be required for these large vessels.     

Radiosurgery and microsurgery for AVMs

We developed a method of velocity-coded color MR angiography using a color code from the data obtained from velocity-phase images of phase-contrast MR angiography in order to add flow direction information to MR angiograms. Phase-contrast MR angiography with reconstruction of velocity-phase images was performed in 30 patients. Two projection images from velocity-phase images of each phase-contrast MR angiogram were obtained and assigned color according to flow direction. We then superimposed the two color images onto the maximum intensity projection image of the MR angiogram. The velocity-coded color MR angiogram clearly showed flow direction from the data on the phase-contrast MR angiogram of the neck. Veins were readily distinguishable from arteries, and flow changes, such as a subclavian steal, were also identified.     

Symptomatic peripheral vascular disease: selection of imaging parameters and clinical evaluation with MR angiography

In the first phase of this study, seven healthy subjects underwent examination with two-dimensional time-of-flight (TOF) magnetic resonance (MR) angiography to develop a protocol for evaluation of peripheral arterial vasculature from the infrarenal aorta to the foot. In the second phase, 73 patients with symptomatic peripheral vascular disease underwent examination with both conventional contrast material-enhanced arteriography and two-dimensional TOF MR angiography to evaluate the clinical usefulness of MR angiography. Postinterventional and intraoperative angiography or direct surgical exploration was the standard of reference. In 32 patients, discrepancies occurred between findings on arteriograms and those on MR angiograms; most of these discrepancies were caused by improved depiction of runoff vessels on MR angiograms. The demonstration with MR angiography of blood vessels not seen on conventional arteriograms, unidentified stenoses, or misidentified blood vessels altered surgical management in 12 patients (16%). Metal-clip artifacts obscured clinically important disease on MR angiograms in two patients. It is concluded that two-dimensional TOF MR angiography is very useful in preoperative assessment of patients with severe peripheral vascular disease.     

Pituitary growth hormone release and gene expression in cafeteria-diet-induced obese rats

PURPOSE: To determine prospectively the feasibility and accuracy of combined gadolinium-enhanced magnetic resonance (MR) angiography, MR urography, and MR nephrography in the presurgical evaluation of potential renal transplant donors. MATERIALS AND METHODS: Twenty-two potential donors for renal transplantation were evaluated with 1.5-T MR imaging. MR angiograms were evaluated for the number of renal arteries, presence of early arterial branches, and renal artery stenoses. The renal collecting system and ureters were evaluated on the MR urograms. Renal parenchyma was assessed on the MR nephrogram. Prospective interpretation of MR images was compared with that of conventional angiograms and excretory urograms and with surgical findings. RESULTS: Gadolinium-enhanced MR angiography enabled correct identification of the arterial supply to all 44 native kidneys (44 single or dominant renal arteries and nine accessory renal arteries), four of five early arterial branches arising in the proximal 2 cm of the renal artery, a mild truncal stenosis in one renal artery, and two anomalies of the draining renal veins. The MR urogram accurately depicted a duplicated collecting system and mild unilateral pelvicalicectasis. The MR nephrogram showed renal size and a solitary cyst in one kidney, confirmed with sonography. CONCLUSION: Combined gadolinium-enhanced MR angiography, MR urography, and MR nephrography can accurately depict the arterial supply, collecting system, and renal parenchyma of donor kidneys.     

Thoracic MR aortography: imaging techniques and strategies

Three-dimensional (3D) gadolinium-enhanced magnetic resonance (MR) angiography is a promising technique for thoracic aortography that complements electrocardiographically gated T1-weighted spin-echo imaging and cine MR imaging. Axial and left anterior oblique T1-weighted spin-echo images are well suited to measurement of aortic dimensions and evaluation of aortic aneurysms. Sagittal and coronal spin-echo images are helpful in evaluation of vascular rings and aortic dissection. Cine gradient-echo and cine phase-contrast imaging allow dynamic evaluation of aortic and valvular flow. Cine phase-contrast imaging also enables noninvasive quantification of blood flow. Capable of being performed during a single breath hold, 3D gadolinium-enhanced MR angiography provides high-resolution 3D data that can be readily used for projection angiography and multiplanar reformation. This technique enables further demonstration of subtle pathologic conditions. Three-dimensional gadolinium-enhanced MR angiography allows more comprehensive and efficient evaluation of the thoracic aorta.     

Iliac artery stenosis measurements: comparison of two-dimensional time-of-flight and three-dimensional dynamic gadolinium-enhanced MR angiography

OBJECTIVE: We compared our ability to make iliac artery measurements on two-dimensional (2D) time-of-flight (TOF) and three-dimensional dynamic gadolinium-enhanced MR angiography with conventional angiography. SUBJECTS AND METHODS: Fifteen patients with lower extremity vascular disease underwent pelvic MR angiography. Parameters of the cardiac-gated axial 2D TOF sequence included a TR/TE of 24/7 msec and a 50 degrees flip angle. Parameters for the three-dimensional MR angiography sequence, in which we obtained 32 coronal 3-mm slices with fat suppression, included a TR/TE of 32/5 msec and a 40 degrees flip angle during infusion of 40 ml of gadolinium-chelated contrast material. Patients then underwent conventional angiography of the iliac arteries. Maximum stenosis in the common iliac, external iliac, and common femoral arteries was then measured. Measurements of stenosis were compared by repeated measures of analysis of variance. Sensitivity and specificity were calculated for identification of greater than or equal to 50% stenosis and less than 50% stenosis. RESULTS: For all vessels studied, we found no significant difference in measurements obtained from the gadolinium-enhanced MR angiography technique and those obtained from conventional angiography (p > .05). However, significantly different stenotic measurements were obtained from the 2D TOF MR angiography sequence and conventional angiography. In the external iliac arteries, 2D TOF MR angiography exaggerated stenoses most substantially. Gadolinium-enhanced MR angiography achieved 100% sensitivity and specificity. CONCLUSION: Dynamic gadolinium-enhanced MR angiography was more accurate than 2D TOF MR angiography when measuring degree of stenosis in the iliac arteries.     

MR angiography with three-dimensional MR digital subtraction angiography

We have developed a time-resolved, contrast-enhanced, volume-imaging technique for magnetic resonance (MR) angiography, known as three-dimensional (3D) MR digital subtraction angiography (DSA). This technique greatly improves MR angiogram quality because it combines the injection of a contrast agent with the ability to image the temporal passage of this agent and, thereby, obviates the need for timing scans or other complicated synchronization schemes. Three-dimensional MR DSA also represents a potential improvement in the sense that, relative to DSA and computed tomography (CT) angiography, the contrast agent is less toxic. Additionally, unlike CT angiography, images may be acquired during the passage of the contrast agent. Therefore, 3D MR DSA shows the sequential passage of contrast through the arterial and venous system, followed by uptake in various organs. Unlike conventional DSA, 3D MR DSA imaging acquires full volume datasets, which allows subsequent reprojection and reformatting. Because images are obtained at approximately 2-6 s time intervals using a temporal aperture on the order of several seconds, motion (such as respiration) causes only a temporary disruption of image quality, similar to that observed in MR fluoroscopy. These temporal characteristics also make the proposed sequence insensitive to variations in the shape and timing of the contrast-pass curve. Although the individual time-resolved images will have somewhat decreased signal-to-noise ratio (SNR) relative to nontime-resolved scans collected in the same acquisition time, the SNR improvement due to the gadolinium appears to accommodate this trade-off. Additionally, if motion between successive images is small, then the full suite of temporal processing schemes, previously investigated in connection with DSA and time-resolved two-dimensional (2D) MR, such as mask mode subtraction, simple matched filtering and Eigen filtering, can be used to obtain composite images. These derived images generally have an increased SNR or negligible venous signal if an arterial-phase image is not obtained in the early time-resolved images. In summary, 3D MR DSA will significantly advance MR angiography because of the following intrinsic advantages: (1) improved signal-to-noise, (2) scan orientation may be chosen independently of the direction of blood flow, (3) uniform vascular signal, even from regions of complex flow, (4) minimization of motion artifacts, (5) greatly reduced sensitivity to variation in the shape and timing of the contrast bolus, (6) ability to be reformatted or reprojected, and (7) ability to apply a variety of temporal postprocessing techniques.     

Intracranial aneurysms: detection and characterization with MR angiography with use of an advanced postprocessing technique in a blinded-reader study

PURPOSE: To assess magnetic resonance (MR) angiography for the detection and characterization of angiographically proved intracranial aneurysms by using an advanced method of postprocessing, in a blinded-reader study. MATERIALS AND METHODS: One hundred fifty-eight vessels were examined with catheter angiography and three-dimensional time-of-flight MR angiography in 44 patients with 63 aneurysms and 15 patients with no aneurysm at catheter angiography. Postprocessing was performed off-line with an advanced multifeature-extraction, ray-tracing algorithm. MR angiograms were interpreted independently by three neuroradiologists blinded to the catheter angiographic results for presence, location, size, and morphology of the aneurysm. Proof of diagnosis was consensus reading of catheter angiograms. RESULTS: Mean sensitivity for detection of aneurysms was 75% (range, 70%-79%). As a screening tool (ie, detection of at least one aneurysm necessitating catheter angiography), mean sensitivity was 91% for all aneurysms and 95% for aneurysms larger than 3 mm. This method was not adequate for detection of lobulation or size of aneurysm. CONCLUSION: MR angiography with an advanced method of postprocessing can result in highly sensitive, specific studies for the diagnosis of intracranial aneurysms that are of sufficient size to be considered for surgical treatment, but it is inadequate for characterization of aneurysms.     

Prevalence and risk factors for diabetic retinopathy among Omani diabetics

To determine the minimal contrast dosage required for diagnostic contrast-enhanced three-dimensional (3D) magnetic resonance angiography (MRA) image quality of the pulmonary (PAs) or renal arteries (RAs). In 12 volunteers (10 females, 2 males; mean age 24 years) imaging was performed with 4 different dosages: 0.05, 0.1, 0.2 and 0.3 mmol/kg of body weight (BW) 0.5 M gadolinium (Gd) contrast agent. The PAs and RAs were evaluated separately each in groups of six volunteers. Qualitative and quantitative signal-to-noise ratio (SNR) image analysis was performed. For the PAs, the increases in signal-to-noise ratio were paralleled by increases in image quality ratings. For the PAs, with the use of 0.05 mmol/kg, only 50.3% of all segments were rated diagnostic, whereas with higher dosages the percentage rose to 89.2% for 0.1 mmol/kg, 98.2% for 0.2 mmol/kg. and 99.1% for 0.3 mmol/kg. For the RAs, 0.3 mmol/kg provided no significant increase in singal-to-noise ratio compared to 0.2 mmol/kg (p = 0.4). Only by a dosage of 0.2 and 0.3 mmol/kg, all evaluated segments were diagnostic evaluable. A dose of 0.2 mmol/kg is required for proper assessment of the RAs or PAs.     

Diagnosis of pulmonary embolism with magnetic resonance angiography

BACKGROUND: Diagnosing pulmonary embolism may be difficult, because there is no reliable noninvasive imaging method. We compared a new noninvasive method, gadolinium-enhanced pulmonary magnetic resonance angiography, with standard pulmonary angiography for diagnosing pulmonary embolism. METHODS: A total of 30 consecutive patients with suspected pulmonary embolism underwent both standard pulmonary angiography and magnetic resonance angiography during the pulmonary arterial phase at the time of an intravenous bolus of gadolinium. All magnetic resonance images were reviewed for the presence or absence of pulmonary emboli by three independent reviewers who were unaware of the findings on standard angiograms. RESULTS: Pulmonary embolism was detected by standard pulmonary angiography in 8 of the 30 patients in whom pulmonary embolism was suspected. All 5 lobar emboli and 16 of 17 segmental emboli identified on standard angiograms were also identified on magnetic resonance images. Two of the three reviewers reported one false positive magnetic resonance angiogram each. As compared with standard pulmonary angiography, the three sets of readings had sensitivities of 100, 87, and 75 percent and specificities of 95, 100, and 95 percent, respectively. The interobserver correlation was good (k=0.57 to 0.83 for all vessels, 0.49 to 1.0 for main and lobar vessels, and 0.40 to 0.81 for segmental vessels). CONCLUSIONS: In this preliminary study, gadolinium-enhanced magnetic resonance angiography of the pulmonary arteries, as compared with conventional pulmonary angiography, had high sensitivity and specificity for the diagnosis of pulmonary embolism. This new technique shows promise as a noninvasive method of diagnosing pulmonary embolism without the need for ionizing radiation or iodinated contrast material.     

The effects of incomplete breath-holding on 3D MR image quality

The purpose of this study was to investigate how fast three-dimensional (3D) MR image quality is affected by breath-holding and to develop an optimal breath-holding strategy that minimizes artifact in the event of an incomplete breath-hold. A computer model was developed to study variable-duration breath-holds during fast 3D imaging. Modeling was validated by 3D gradient-echo imaging performed on 10 volunteers. Signal-to-noise ratio (SNR) and image blur were measured for both simulated and clinical images. Insights gained were applied to clinical 3D gadolinium-enhanced MR angiography. Breath-holding significantly improved abdominal 3D MR image quality. Most of this benefit could be achieved with a breath-hold fraction of 50% if it occurred during acquisition of central k space. Breath-holding during peripheral k-space acquisition, however, had no significant benefit. Respiratory motion artifact on fast 3D MRI occurring when a patient fails to suspend respiration for the entire scan duration can be minimized by collecting central k space first (centric acquisition) so that premature breathing affects only the acquisition of peripheral k space.     

MR angiography in the preoperative evaluation of abdominal aortic aneurysms: a preliminary study

PURPOSE: The ability of magnetic resonance (MR) angiography to depict visceral and renal vessels was evaluated in patients with abdominal aortic aneurysms (AAAs). PATIENTS AND METHODS: MR sequences (sagittal T1-weighted, two-dimensional coronal, and three-dimensional axial time-of-flight) were compared in a prospective blinded fashion with conventional angiograms obtained preoperatively in 23 patients with AAAs. Results were correlated with surgical findings when available. RESULTS: Operative aortic clamp site was correctly predicted with conventional angiography in 95% of patients and with MR angiography in 86% (P > .1). Aneurysm neck measurements obtained with the two modalities were within 1 cm in 91% of cases. With conventional angiography as the standard of reference, 96% of all renal arteries were identified on MR angiograms but 36% of accessory arteries were missed. MR angiography enabled identification of patients who had at least one renal artery stenosis greater than 50% with a sensitivity of 100% and specificity of 89%. For identifying individual renal artery, celiac artery, and superior mesenteric artery stenoses of similar severity, the sensitivity and specificity were 67% and in excess of 96%, respectively. The celiac artery could not be evaluated in one case. CONCLUSION: The results of this small study suggest that the role of MR angiography in the preoperative evaluation of AAA warrants further investigation.     

Nontumorous hepatic pseudolesion around the falciform ligament: prevalence on gadolinium chelate-enhanced MR examination

OBJECTIVE: Our objective was to determine the prevalence of nontumorous hepatic pseudolesions seen around the falciform ligament on dynamic spoiled three-dimensional (3D) gradient-recalled echo (GRE) MR imaging obtained during i.v. injection of a gadolinium chelate. SUBJECTS AND METHODS: The gadolinium chelate-enhanced spoiled 3D GRE examinations of the liver of 103 patients were prospectively analyzed by two readers for the presence of a nontumorous hepatic pseudolesion around the falciform ligament to determine the prevalence of this finding. For all pseudolesions, pathologic examination or follow-up imaging studies excluded true tumors. RESULTS: A total of 15 nontumorous hepatic pseudolesions were found on 13 (13%) of 103 examinations. The size of pseudolesions ranged from 5 to 15 mm (mean, 9 mm). Twelve pseudolesions were located in segment IV, and three were in segment III. On two MR examinations, two pseudolesions (one in segment IV and one in segment III) were found. Fourteen (93%) of 15 pseudolesions were seen during the arterial phase of the bolus injection. All pseudolesions (100%) were seen during the portal phase, and one pseudolesion (7%) remained visible during the equilibrium phase. The presence of true tumors was excluded in one case by pathologic examination and in twelve cases by follow-up imaging examinations. CONCLUSION: Nontumorous hepatic pseudolesions around the falciform ligament are not rarely seen on gadolinium chelate-enhanced spoiled 3D GRE examinations. Thus, recognition of these pseudolesions is crucial because they may be misinterpreted as true tumors.     

Magnetic resonance urography by breath-hold contrast-enhanced three-dimensional FISP

The purpose of this study was to present our initial experience with contrast-enhanced MR urography with a breath-hold three-dimensional imaging technique. We performed MR urographic studies in two pigs (four studies) and five human subjects using gadopentetate dimeglumine. The FISP sequence we used was the same as the one used for contrast-enhanced three-dimensional breath-hold angiography. MR three-dimensional urograms were obtained 7-24 minutes after the contrast injection with a dose as low as .03 mmol/kg. The calyces, renal pelves, and ureters were very well visualized. Three-dimensional MR urography can be acquired within a single breath-hold after administration of gadolinium chelates. This technique could become part of a protocol that could potentially lead to a single comprehensive diagnostic workup for suspected ureteral obstruction and gross hematuria.     

MR angiography of the portal venous system: techniques, interpretation, and clinical applications

Magnetic resonance (MR) angiography is a noninvasive means of assessing the portal venous system that has potential advantages over currently used modalities. Time-of-flight and phase-contrast MR angiography are useful techniques that differ fundamentally in their means of data acquisition but are comparable in their ability to demonstrate normal anatomy as well as abnormalities of the portal venous system. Occasionally, artifacts caused by respiratory motion, implanted metallic devices or surgical clips, in-plane saturation, or areas of complex flow are seen at MR angiography of the portal venous system. However, most artifacts can easily be identified as such and either remedied or ignored. In addition, the suppression of signal from surrounding soft tissues may result in poor detection of parenchymal lesions. The utility of standard projection angiograms and source images can be increased through the use of intravenously administered contrast material and postprocessing techniques such as partial-volume maximum intensity projection reconstructions and shaded surface renderings. In addition to providing information on portal venous anatomy and portosystemic collateral vessels, MR angiography of the portal vein has clinical application in portal venous thrombosis and stenosis, liver transplantation, and the evaluation and planning of surgical and transjugular intrahepatic portosystemic shunts.     

Vessel enhancement filtering in three-dimensional MR angiograms using long-range signal correlation

Small vessels in three-dimensional MR angiograms have low visibility in maximum-intensity projection images because of their low contrast. In a previous study, we had two nonlinear filters that appeared to give significant improvement in small vessel detail. In this paper, we report on a generalization of this filter that allows a more general modeling of the vessels and a more complete suppression of background. One implementation of the general filter gave a vessel mean contrast-to-noise ratio that is 2.52 and 3.51 times higher than the vessel mean contrast-to-noise ratio obtained using our previously reported maximum-minimum (max-min) filter and cross-section filter, respectively.     

CADASIL in a North American family: clinical, pathologic, and radiologic findings

Spoiled fast three-dimensional gradient-echo magnetic resonance imaging of the aorta and iliac arteries was performed in 13 patients after administration of a single bolus of gadopentetate dimeglumine. The imaging table was moved manually 40-45 cm between two acquisitions. Arterial signal-to-noise ratio did not vary significantly between the thoracic (aortic) and pelvic stations, but venous signal-to-noise ratios increased and arterial contrast-to-noise ratios decreased on the pelvic studies. This method was feasible and increased anatomic coverage.