Carotid artery stenosis: accuracy of contrast-enhanced MR angiography for diagnosis

PURPOSE: To assess accuracy of contrast material-enhanced magnetic resonance (MR) angiography as compared with three-dimensional (3D) time-of-flight (TOF) MR angiography and reference digital subtraction angiography (DSA) in diagnosis of carotid artery stenosis. MATERIALS AND METHODS: Enhanced and 3D TOF MR angiography and DSA were performed in 51 consecutive patients suspected of having carotid artery stenosis at duplex ultrasonography. Stenoses were measured by two independent observers blinded to clinical information and other test results. Pearson correlation coefficients were used, and kappa for interobserver variabilities was estimated. Sensitivity and specificity of enhanced and 3D TOF MR angiography were calculated and compared with those of DSA. RESULTS: Pearson correlation coefficients were 0.94 (P <.01) for enhanced angiography versus DSA, 0.92 (P <.01) for 3D TOF angiography versus DSA, and 0.93 (P <.01) for enhanced versus 3D TOF angiography for observer 1 and 0.94 (P <.01), 0.95 (P <.01), and 0.94 (P <.01), respectively, for observer 2. kappa statistics were 0.81 for enhanced angiography, 0.79 for 3D TOF angiography, and 0.78 for DSA. Stenosis measurements of observer 1 at enhanced MR angiography, with inclusion of carotid arteries on the symptomatic side only, compared with those of DSA yielded a sensitivity of 90% (95% CI: 68%, 99%) and a specificity of 77% (95% CI: 55%, 92%). 3D TOF angiography yielded a sensitivity of 86% (95% CI: 67%, 97%) and a specificity of 73% (95% CI: 50%, 89%) compared with those of DSA. For observer 2, sensitivity and specificity for enhanced angiography were 91% (95% CI: 70%, 99%) and 76% (95% CI: 52%, 91%), respectively, and 90% (95% CI: 68%, 99%) and 77% (95% CI: 51%, 92%), respectively, for 3D TOF angiography. CONCLUSION: Accuracy of enhanced MR angiography in diagnosis of severe stenosis is similar to that of 3D TOF MR angiography.     

Carotid artery stenosis: intraindividual correlations of 3D time-of-flight MR angiography, contrast-enhanced MR angiography, conventional DSA, and rotational angiography for detection and grading

PURPOSE: To compare three-dimensional (3D) time-of-flight (TOF) MR angiography, contrast-enhanced MR angiography, digital subtraction angiography (DSA), and rotational angiography for depiction of stenosis. MATERIALS AND METHODS: The study had Ethics Committee approval, and each patient gave written informed consent. Forty-nine patients (18 women, mean age, 67.2 years +/- 9.1 [+/- standard deviation], and 31 men, mean age, 63.1 years +/- 8.0) with symptomatic stenosis of internal carotid artery (ICA) diagnosed at duplex ultrasonography underwent transverse 3D TOF MR angiography with sliding interleaved kY acquisition and coronal contrast-enhanced MR angiography, followed by DSA and rotational angiography within 48 hours. MR angiography was performed at 1.5-T with a cervical coil. Contrast-enhanced MR angiograms were obtained after a bolus injection of 20 mL of gadobenate dimeglumine. Maximum ICA stenosis on maximum intensity projection and source images was quantified according to NASCET criteria. Correlations for 3D TOF MR angiography, contrast-enhanced MR angiography, DSA, and rotational angiography were determined by means of cross tabulation, and accuracy for detection and grading of stenoses were calculated. Data were evaluated with analysis of variance, Wilcoxon signed rank test, and McNemar test, all at significance of P < .05. RESULTS: Ninety-eight ICAs were evaluated at contrast-enhanced MR angiography, DSA, and rotational angiography, and 97 were evaluated at 3D TOF MR angiography. Correlations for contrast-enhanced MR angiography, 3D TOF MR angiography, and DSA relative to rotational angiography were r2 = 0.9332, r2 = 0.9048, and r2 = 0.9255, respectively. Lower correlation (r2 = 0.8593) was noted for contrast-enhanced MR angiography and DSA. Respective sensitivity and specificity for detection of hemodynamically relevant stenosis relative to rotational angiography were 100% and 90% for contrast-enhanced MR angiography, 95.5% and 87.2% for 3D TOF MR angiography, and 88.6% and 100% for DSA. Four of 31 severe stenoses were underestimated at DSA, and three were underestimated at contrast-enhanced MR angiography. Three severe stenoses were underestimated at 3D TOF MR angiography, and one was misclassified as occluded. Of 13 moderate (50%-69%) stenoses, one was overestimated at contrast-enhanced MR angiography, two were underestimated and three overestimated at 3D TOF MR angiography, and two were underestimated at DSA. CONCLUSION: DSA results in an underestimation of ICA stenosis compared with rotational angiography. Contrast-enhanced MR angiography correlates best with rotational angiography.     

MR angiography of the intracranial venous system

PURPOSE: To compare the effectiveness of different imaging planes at time-of-flight (TOF) magnetic resonance (MR) angiography and phase-contrast MR angiography in the visualization of the normal intracranial venous system. MATERIALS AND METHODS: In 12 healthy volunteers, two-dimensional (2D) TOF MR angiography and three-dimensional (3D) phase-contrast MR angiography were performed in transverse, sagittal, and coronal planes. All data were displayed as maximum intensity projection (MIP) images. Four neuroradiologists assessed the visibility of 28 intracranial venous structures on the MIP images. Statistical analysis was performed by using the Friedman two-way analysis of variance and the Cochran Q test. RESULTS: Visualization of the normal intracranial venous system was better with 3D phase-contrast and coronal 2D TOF MR angiography than with transverse or sagittal 2D TOF MR angiography (P < .05, Friedman test) for each observer and the group of observers. Differences were found between each of the 2D TOF and 3D phase-contrast MR angiographic sequences in the visualization of individual venous structures (Cochran Q test). The kappa values ranged from 0.36 to 0.71, which indicated a moderate to good agreement between observers. CONCLUSION: The normal intracranial venous system is adequately visualized with 3D phase-contrast and coronal 2D TOF MR angiography.     

Improved image quality of intracranial aneurysms: 3.0-T versus 1.5-T time-of-flight MR angiography

BACKGROUND AND PURPOSE: We hypothesize that the nearly doubling of signal-to-noise ratio at 3.0 T compared with that at 1.5 T yields improved clinical MR angiograms and enables superior visualization of intracranial aneurysms. The goal of this study was to determine whether 3.0-T time-of-flight (TOF) MR angiography is superior to 1.5-T TOF MR angiography in the detection and characterization of intracranial aneurysms. METHODS: Fifty consecutive patients referred for MR angiography of a known or suspected intracranial aneurysm underwent 3-T TOF MR angiography. Seventeen of these 50 patients had also previously undergone 1.5-T TOF MR angiography and these images were used as a basis for comparison with images obtained at 3.0 T. Fourteen of 23 patients in whom aneurysms were identified also underwent prior conventional angiography, which was used as the reference standard. Readers blinded to patient history identified the presence and location of aneurysm(s) on angiograms and graded images for overall image quality by using a five-point scale. RESULTS: Twenty-eight aneurysms were identified in 23 of 50 patients. Seventeen aneurysms in 17 patients had been documented with 1.5-T MR angiography. The 3.0-T technique had a higher mean image quality score than that of the 1.5-T MR technique (P <.0001). Both 3.0-T and 1.5-T TOF MR angiography depicted all the aneurysms that had been documented by conventional angiography. CONCLUSION: 3D TOF MR angiography at 3 T offers superior depiction of intracranial aneurysms compared with that of 1.5-T TOF MR angiography.     

Determination of optimal injection parameters for intraarterial gadolinium-enhanced MR angiography

PURPOSE: Rapid vascular depiction with use of a minimum of gadolinium (Gd) contrast agent will be required to generate road-map vascular images for magnetic resonance (MR) imaging-guided endovascular interventions. The objective of this study was to optimize intraarterial injections of MR contrast agent during magnetic resonance angiography (MRA), obtained during interventions, by determining the optimal Gd vascular concentration ([Gd]) for vessel depiction. MATERIALS AND METHODS: The authors derived theoretical expressions to estimate the [Gd] resulting in maximal signal in blood. A model was developed to account for flow dilution to estimate [Gd] given the injected Gd concentration, injection rate, and the blood flow rate. Experiments in four animals (three dogs, one pig) were conducted to verify this model with use of both time-resolved two-dimensional (2D) thick-slab and single-phase three-dimensional (3D) MRA acquisitions. The authors also determined the optimal [Gd] required for vessel depiction in animal models. RESULTS: The theoretical expressions yielded optimal [Gd] of 10.2 mmol/L in blood. The animal experiments used the flow dilution model and examined signal enhancement in the aorta and the renal and iliac arteries. Maximal enhancement occurred at [Gd] = 16.2 +/- 4.0 mmol/L (mean +/- SE). CONCLUSIONS: The theoretically predicted values for [Gd]optimal and the flow dilution model were successfully validated. The relationship between injected [Gd], injection rate, and blood flow rate permits rapid intraarterial administration of contrast material, using less overall contrast material than with standard intravenous Gd-enhanced MRA.     

Peripheral arteries in diabetic patients: standard bolus-chase and time-resolved MR angiography

PURPOSE: To prospectively determine the diagnostic performance of a combination of standard bolus-chase magnetic resonance (MR) angiography and MR angiography with time-resolved imaging of contrast kinetics (TRICKS) for depicting severity of peripheral vascular disease of the lower extremity, including the pedal arteries, in diabetic patients with digital subtraction angiography (DSA) as the reference standard. MATERIALS AND METHODS: An ethical committee approved this study; written informed consent was obtained from patients. Standard three-station and TRICKS MR angiography of the calf and foot were performed in 31 consecutive diabetic patients (23 men, eight women; mean age, 67 years; range, 43-81 years). Two readers separately assessed images of arterial segments as diagnostic or nondiagnostic and graded stenosis. Results were compared with those at DSA when the corresponding arterial segments were considered diagnostic at DSA. Wilcoxon signed rank test was used to determine if a significant difference between imaging techniques existed, and kappa statistics were used to determine interobserver agreement. RESULTS: The difference between standard MR angiography and DSA regarding the number of diagnostic segments in the thigh was not significant (P = .50). A significantly higher number of calf and foot segments was considered diagnostic at TRICKS MR angiography than at standard MR angiography (P < .025). Sixteen of 26 segments in the foot that were considered nondiagnostic at DSA were considered diagnostic at TRICKS MR angiography. Average sensitivity of standard MR angiography for depicting hemodynamically significant arterial stenosis was 84% (reader 1) and 83% (reader 2) in the thigh and 78% (reader 1) and 80% (reader 2) in the calf. For both readers, average specificity was 97% in the thigh and 90% in the calf. Sensitivity and specificity of TRICKS MR angiography in the calf and foot were improved compared with those at standard MR angiography. CONCLUSION: TRICKS MR angiography of the distal calf and pedal vessels is superior to standard MR angiography regarding the number of diagnostic segments and assessment of the degree of luminal narrowing.     

Vascularization of head and neck paragangliomas: comparison of three MR angiographic techniques with digital subtraction angiography

BACKGROUND AND PURPOSE: MR angiography of the head and neck region has been studied widely, but few studies have been performed concerning the efficacy of MR angiography for the identification of the specific vascular supply of the highly vascular head and neck paragangliomas. In this study, we compared three MR angiography techniques with respect to visualization of branch arteries in the neck and identification of tumor feeders in patients with paragangliomas. METHODS: Fourteen patients with 29 paragangliomas were examined at 1.5 T using 3D phase-contrast (PC), 2D time-of-flight (2D TOF), and multi-slab 3D TOF MR angiography. In the first part of the study, two radiologists independently evaluated the visibility of first-, second-, and third-order branch arteries in the neck. In the second part of the study, the number of feeding arteries for every paraganglioma was determined and compared with digital subtraction angiography (DSA), the standard of reference in this study. RESULTS: Three-dimensional TOF angiography was superior to the other MR angiography techniques studied (P < .05) for depicting branch arteries of the external carotid artery in the neck, but only first- and second-order vessels were reliably shown. DSA showed a total of 78 feeding arteries in the group of patients with 29 paragangliomas, which was superior to what was revealed by all MR angiography techniques studied. More tumor feeders were identified with 3D TOF and 2D TOF angiography than with 3D PC MR angiography (P < .05), with a sensitivity/specificity of 61%/98%, 54%/95%, and 31%/95%, respectively. Sensitivity was lowest for carotid body tumors. CONCLUSION: Compared with intra-arterial DSA, the 3D TOF MR angiography technique was superior to 3D PC and 2D TOF MR angiography for identifying the first- and second-order vessels in the neck. With 3D TOF angiography, more tumor feeders were identified than with the other MR angiography techniques studied. The sensitivity of MR angiography, however, is not high enough to reveal important vascularization. The sensitivity of MR angiography is too low to replace DSA, especially in the presence of carotid body tumors.     

Diagnostic accuracy of time-resolved 2D projection MR angiography for symptomatic infrapopliteal arterial occlusive disease

OBJECTIVE: Our objective was to evaluate the diagnostic accuracy of time-resolved 2D projection MR angiography in detecting calf and pedal artery occlusive disease. MATERIALS AND METHODS: Time-resolved MR angiography of calf and pedal arteries was performed on 59 symptomatic legs of 52 patients using the head coil and bolus injections of 6 mL of gadolinium contrast medium. Selective X-ray digital subtraction angiography was performed within 30 days after MR angiography. Calf and pedal arteries were divided into 10 segments. X-ray digital subtraction angiography and MR angiography images were retrospectively interpreted by three expert observers, who graded segments as having no significant stenosis, significant stenosis (> 50%), or occlusion. The accuracy of MR angiography interpretations was compared with the accuracy of consensus X-ray digital subtraction angiography interpretations as the standard of reference. Arterial segments with discrepant grading on X-ray digital subtraction angiography and MR angiography were reviewed again to determine the reasons for disagreement. RESULTS: Arterial phase MR angiography images free of venous contamination were obtained in every case. The agreement between MR angiography and X-ray digital subtraction angiography in depicting infrapopliteal arterial disease was fair to good (kappa = 0.44-0.92). Overall sensitivity and specificity were 83% and 87%, respectively, for detecting significant stenosis of calf and pedal arteries and 86% and 93%, respectively, for detecting occlusions. Accuracy was higher in the larger vessels-for example, calf (84%) compared with foot (71%). In 21% (22/105) of the segments graded differently on MR angiography than on X-ray digital subtraction angiography, it was believed that MR angiography was more likely to be correct than X-ray digital subtraction angiography because of visualization of late-filling arteries on MR angiography that did not opacify on X-ray digital subtraction angiography. CONCLUSION: Time-resolved 2D projection MR angiography accurately evaluates calf and pedal arteries without degradation from venous contamination.     

The value of MR angiography techniques in the detection of head and neck paragangliomas

OBJECTIVE: The objective of this study was to compare three-dimensional phase-contrast angiography (3D PCA), 2D time-of-flight (2D TOF), and 3D TOF magnetic resonance (MR) angiography and a proton density weighted technique in terms of their ability to detect head and neck paragangliomas. MATERIALS AND METHODS: 14 patients with 29 paragangliomas were examined at 1.5 T. Three MR angiography sequences (3D PCA, 2D TOF, and multi-slab 3D TOF) and a proton density (PD) weighted sequence were reviewed by four neuroradiologists. The gold standard was digital subtraction angiography. Presence of tumor was assessed in five grades of confidence. Sensitivity and specificity were calculated after dichotomizing the results. Data was analyzed using the logistic regression method. RESULTS: Mean sensitivity and specificity for the four observers were for PD: 72%/97%, for 3D PCA: 75%/90%, for 2D TOF: 66%/93%, and for 3D TOF: 90%/92%. Sensitivity was significantly better for 3D TOF MRA (P < 0.001). No substantial between-observer variation for tumor detection was present. CONCLUSION: Our results demonstrate that, using 3D TOF MRA, paragangliomas in the head and neck region can be detected with high sensitivity and specificity. Further investigation is necessary to judge the value of 3D TOF MR angiography against fat suppressed contrast enhanced T1 weighted and fat suppressed T2 weighted MR sequences to find the optimal imaging sequence for paragangliomas.     

Accuracy of pre- and postcontrast 3D time-of-flight MR angiography in patients with acute ischemic stroke: correlation with catheter angiography

BACKGROUND AND PURPOSE: 3D time-of-flight (TOF) MR angiography (MRA) is insensitive to slow flow; however, the use of MR imaging contrast agents helps to visualize slow-flow vessels and avoids overestimation of vascular occlusion. The purpose of this study was to correlate pre- and postcontrast 3D TOF MRA with the results of conventional angiography during endovascular reperfusion therapy and to determine the accuracy of postcontrast 3D TOF MRA. MATERIALS AND METHODS: Thirteen patients who underwent endovascular reperfusion therapy for acute ischemic stroke were retrospectively analyzed. MR imaging techniques included single-slab 3D TOF MRA with and without contrast, as well as perfusion-weighted imaging. Angiography during reperfusion therapy was used as a standard of reference. Affected arteries were divided into segments either proximal or distal to the lesion, and pre- and postcontrast MRA signals were graded as absent, diminished or narrowed, or normal. RESULTS: In 2 of 5 patients with arterial stenosis and 6 of 8 patients with complete occlusion, MRA signal intensity proximal to each lesion was absent, indicating a proximal pseudo-occlusion on precontrast MRA. Postcontrast MRA demonstrated an arterial signal intensity proximal to the stenotic or occlusive lesions in all 13 patients. Arterial signal intensity distal to the occlusion was identified on postcontrast MRA in 7 of 8 patients having complete occlusion, and the extent of occlusion on postcontrast MRA was similar to results of conventional angiography. CONCLUSION: In this small series, postcontrast 3D TOF MRA more accurately delineated the extent of stenotic or occlusive arterial lesions than precontrast MRA.     

Three-dimensional time-of-flight MR angiography with a specialized gradient head coil

A gradient head coil has been developed, incorporating two independent gradients within the conventional body coil of the magnetic resonance (MR) system, with reduced rise times (200 μsec) and maximum amplitudes of 37 and 18 mT/m in the z and y directions, respectively. This gradient coil was systematically evaluated by testing two-dimensional (2D) and three-dimensional (3D) time-of-flight (TOF) MR angiography sequences applied to a pulsatile flow phantom simulating a carotid stenosis and the intracranial vasculature. When standard 2D and 3D TOF MR angiography techniques were used to image the carotid stenosis model, dramatic signal loss in the stenotic segment and a large flow void distal to the stenosis were seen. The shorter (3.8 msec) absolute echo times (TEs) achievable with the gradient coil in 3D sequences substantially reduced the phase dispersion and associated signal loss in the region of stenosis. Shorter TEs alone (3.2 msec) did not minimize signal loss, and firstorder flow compensation in the read and section-select directions provided further improvements (despite slightly longer TEs). Reduction of TEs in 2D sequences yielded relatively poor results regardless of the refocusing scheme or TE. This study confirms the predicted benefits of a dedicated coil with improved gradient capabilities for 3D MR angiography. The study suggests the limitations of 2D TOF MR angiography in the evaluation of severe stenoses.     

Prominent laterality of the posterior cerebral artery at three-dimensional time-of-flight MR angiography in M1-segment middle cerebral artery occlusion

BACKGROUND AND PURPOSE: Three-dimensional time-of-flight MR angiography (3D TOF MRA) often discloses prominent posterior cerebral artery (PCA) laterality in the setting of M1-segment middle cerebral artery (MCA) occlusion. We sought to analyze the implications of prominent PCA laterality at 3D TOF MRA. METHODS: We retrospectively reviewed 3D TOF MRA and digital subtraction angiography (DSA) findings in 25 patients (12 male, 13 female; mean age, 68.8 years [age range, 29-94 years]) with M1-segment occlusion. The observable laterality of the PCA, determined on the basis of 3D TOF MRA findings, was scored according to distal signal extent and compared with findings of collateral flow from the ipsilateral PCA via the leptomeningeal anastomosis (LMA) at DSA. Frequency of PCA laterality at 3D TOF MRA in patients and that in 56 healthy control subjects was also compared. RESULTS: The positive predictive value of PCA laterality for the existence of collateral flow was 99.9% and the negative predictive value 30.7%. The distal extent of ipsilateral PCA signal at 3D TOF MRA positively correlated with the grade of collateral flow from the PCA via the LMA (r = 0.802; P <.01). PCA laterality was significantly less common in control subjects (P <.01). CONCLUSION: Prominent PCA laterality at 3D TOF MRA in patients with M1-segment occlusion represents the existence of collateral flow from the PCA via the LMA.     

Multidirectional depiction of internal carotid arterial stenosis: three-dimensional time-of-flight MR angiography versus rotational and conventional digital subtraction angiography

PURPOSE: To evaluate whether and to what extent greater number of projection images obtained at three-dimensional (3D) time-of-flight (TOF) magnetic resonance (MR) angiography versus conventional digital subtraction angiography (DSA) causes overestimation of internal carotid arterial (ICA) stenosis. MATERIALS AND METHODS: DSA (two or three projections), rotational angiography (16 or 32 projections), and 3D TOF MR angiography (12 projections) were performed in 47 stenotic ICAs of 38 symptomatic patients. Two observers independently measured maximum stenosis, and the mean differences among MR angiography, DSA, and rotational angiography were compared. RESULTS: Three rotational and five MR angiograms were nondiagnostic. Seven MR angiograms of ICA stenoses showed a signal void and were excluded from analysis. On the remaining 32 angiograms, mean differences in maximum stenosis for observers 1 and 2, respectively, were 7% (95% CI: 3%, 12%) and 8% (95% CI: 3%, 13%) at MR angiography versus DSA and 2% (95% CI: -2%, 7%) and -1% (95% CI: -5%, 3%) at MR angiography versus rotational angiography. ICA stenosis was graded significantly higher at MR angiography versus DSA, whereas, it was not overestimated at MR angiography versus rotational angiography. The difference in maximum stenosis at MR angiography versus DSA was significantly different from that of MR angiography versus rotational angiography. CONCLUSION: Apparent overestimation of ICA stenosis at 3D TOF MR angiography versus conventional DSA may be partly explained by the greater number of projection images available at 3D TOF MR angiography.     

MR angiography of the renal artery: comparison of breath-hold two-dimensional phase-contrast cine technique with the phased-array coil and breath-hold two-dimensional time-of-flight technique with the body coil

Breath-hold 2D phase-contrast (PC) cine MR angiography with a phased-array coil and 2D time-of-flight (TOF) MR angiography were performed in the renal arteries and their findings were compared. Breath-hold 2D thin slice PC and TOF MR angiography were performed in 10 normal volunteers for renal arteries. A PC technique with k-space segmentation was utilized with the phased-array coil. A PC technique provided visualization of the renal artery more distally than a TOF technique (4.8 ± 0.5cm vs.3.7 ± 0.8 cm). With cardiac triggering, distal renal arteries were well demonstrated in PC MR angiography. On PC images, up- or downward movements of the mid to distal renal arteries with aortic pulsatility were recognized. The quality of the images was better with the PC than with the TOF technique (3.4 vs. 2.7). The mid to distal portions of the renal arteries translationally move with aortic pulsatility. To consistently visualize and evaluate them on MR angiography, cardiac triggering might be required to reduce the effects of pulsatile motions of the renal artery in the use of a phased-array coil.     

Intraarterial gadolinium-enhanced 2D and 3D MR angiography: a preliminary study

PURPOSE: To evaluate, in phantom and canine models, intraarterial gadolinium-enhanced two-dimensional (2D) and three-dimensional (3D) magnetic resonance angiography (MRA). MATERIALS AND METHODS: The in vitro experiments examined gadodiamide solutions ranging in gadolinium (Gd) concentration from 0.1% to 100%. A spoiled gradient-recalled echo (SPGR) sequence was used with various repetition time/echo time (TR/TE) parameters. Signal was measured to determine which concentration yielded the highest signal. For in vivo experiments, pigtail catheters were placed in the abdominal aortae of two dogs. Intraarterial injections of 20-30 mL of 0.5%-25% Gd solutions were performed. We acquired images with use of 2D and 3D SPGR techniques. Depiction of the abdominal aortae and renal vessels was assessed qualitatively and quantitatively. RESULTS: Phantom experiments demonstrated that a 2%-6% solution of Gd produced the highest MR signal, depending on the imaging parameters. In the canine model, a 2% Gd solution was best for 2D techniques, whereas 7%-14% Gd solutions were optimal for 3D techniques. CONCLUSIONS: Intraarterial contrast material-enhanced 2D and 3D MRA can be successfully implemented with use of dilute Gd. Dilution permits the administration of more intraarterial injections per day, without exceeding the dose limit, compared with intravenous Gd-enhanced MRA. Intraarterial injections also limit scan synchronization and contrast material dispersion issues. This technique may have application in MR-guided endovascular procedures.     

Diabetes and peripheral arterial occlusive disease: prospective comparison of contrast-enhanced three-dimensional MR angiography with conventional digital subtraction angiography

OBJECTIVE: The purpose of this study was to compare contrast-enhanced three-dimensional MR angiography with conventional digital subtraction angiography (DSA) for identifying and evaluating arteries of the distal calf and foot in diabetic patients with severe arterial occlusive disease who will undergo distal bypass surgery. SUBJECTS AND METHODS: Twenty-four feet of 24 consecutive patients with diabetes and limb-threatening lower extremity ischemia were prospectively imaged using an ultrafast three-dimensional fast low-angle shot sequence on a 1.5-T MR scanner. All patients also underwent DSA of the diseased extremity within 5 days. Images were interpreted in a randomized manner by two observers in conference. Each lower extremity was divided into seven potential arterial segments. Image analysis included the detection of patent, stenosed, or occluded vessel segments. A vascular surgeon formulated treatment plans on the basis of findings from DSA and then formulated treatment plans on the basis of findings from both DSA and MR angiography. RESULTS: MR angiography was significantly better than DSA in revealing peripheral runoff vessels (p < 0.001). In nine (38%) of the 24 patients, MR angiography showed patent pedal vessels suitable for distal bypass grafting that were not revealed by DSA. Because of the results of MR angiography, treatment plans changed in seven of the nine patients in whom patent vessels were subsequently used as target vessels for distal pedal bypass grafts. CONCLUSION: Contrast-enhanced three-dimensional MR angiography is superior to DSA in revealing patent vessel segments of the foot in diabetic patients with severe arterial occlusive disease. Contrast-enhanced three-dimensional MR angiography should be part of the diagnostic algorithm for patients in whom pedal bypass grafting is a therapeutic option.     

3.0-Tesla MR angiography of intracranial aneurysms: comparison of time-of-flight and contrast-enhanced techniques

PURPOSE: To determine whether 3.0-T elliptical-centric contrast-enhanced (CE) magnetic resonance (MR) angiography is superior to 3.0-T elliptical-centric time-of-flight (TOF) MR angiography in the detection and characterization of intracranial aneurysms, and to determine whether increasing the acquisition matrix size in 3.0-T CE MR angiography improves image quality. MATERIALS AND METHODS: A total of 50 consecutive patients referred for MR angiographic evaluation of a known or suspected intracranial aneurysm underwent MR angiography, including three-dimensional TOF and elliptical-centric CE techniques at 3.0 T. The 3.0-T three-dimensional TOF and 3.0-T CE examinations were graded for image quality. A blind review identified the presence and location of aneurysms. RESULTS: A total of 28 aneurysms were identified in 23 of the 50 patients. The 3.0-T TOF MR angiography had a higher mean score for image quality than the 3.0-T elliptical-centric CE MR angiography (P < 0.0001). A total of 14 patients with aneurysms had conventional angiography for comparison. The 3.0-T TOF showed all the aneurysms, whereas 3.0-T CE MR angiography did not show 1 of 19 aneurysms when conventional angiography was the reference standard. CONCLUSION: For imaging intracranial aneurysms, 3.0-T TOF MR angiography offers better image quality than 3.0-T CE MR angiography using the elliptical-centric technique.     

Validation of injection parameters for catheter-directed intraarterial gadolinium-enhanced MR angiography

RATIONALE AND OBJECTIVES: Catheter-directed intraarterial (IA) injections of gadolinium contrast agents may be used during endovascular interventions with magnetic resonance (MR) imaging guidance. Injection protocols require further validation. Using a flow phantom and swine, the authors aimed to (a) measure the optimal arterial gadolinium concentration ([Gd]) required for MR angiography and (b) validate a proposed IA injection protocol for gadolinium-enhanced MR angiography. MATERIALS AND METHODS: For in vitro experiments, the authors placed a catheter in the aorta of an aorto-renal-iliac flow phantom. Injected [Gd], injection rates, and aortic blood flow rates were varied independently for 36 separate IA gadolinium injections. The authors performed 2D and 3D MR angiography with a fast spoiled gradient-recalled echo sequence. For subsequent in vivo experiments, they selectively placed catheters within the aorta, renal artery, or common iliac artery of three pigs. Injection rate and injected [Gd] were varied. The authors performed 32 separate IA gadolinium injections for 2D MR angiography. Signal-to-noise ratios (SNRs) were compared for the various combinations of injection rate and injected [Gd]. RESULTS: In vitro, an arterial [Gd] of 2%-4% produced an optimal SNR for 2D MR angiography, and 3%-5% was best for 3D MR angiography. In swine, an arterial [Gd] of 1%-4% produced an optimal SNR. In the phantom and swine experiments, SNR was maintained at higher injection rates by inversely varying the injected [Gd]. CONCLUSION: Dilute arterial [Gd] is required for optimal IA gadolinium-enhanced MR angiography. To maintain an optimal SNR, injection rates and injected [Gd] should be varied inversely. The postulated injection protocol was validated.     

Distal lower extremity imaging: prospective comparison of 2-dimensional time of flight, 3-dimensional time-resolved contrast-enhanced magnetic resonance angiography, and 3-dimensional bolus chase contrast-enhanced magnetic resonance angiography

OBJECTIVE: To compare the 2-dimensional time of flight, the 3-dimensional time-resolved contrast-enhanced magnetic resonance (MR) angiography, and the 3-dimensional 3-station bolus chase contrast-enhanced MR angiography in assessing distal station atherosclerosis. METHODS: Two-dimensional time of flight, 3-dimensional time-resolved contrast-enhanced MR angiography, and 3-dimensional bolus chase contrast-enhanced MR angiography were performed from the knees to the metatarsal heads of 40 patients. Blinded to the patients' identity, 2 readers independently reviewed the 3 sequences in random order; differences were resolved by consensus. Anterior tibial, peroneal, and posterior tibial arterial lengths to the talar dome were scored as follows: 1, greater than 50% of the length of a normal artery; 2, less than 50%; and 3, total occlusion. Stenoses were scored as follows: 1, less than 50%; and 2, greater than 50%. The pedal vessels (dorsalis pedis, posterior tibial, and plantar pedal arch arteries) were scored as follows: 1, less than 50% stenosis; and 2, greater than 50% stenosis. The reference standard was a combined interpretation of all 3 sequences by both readers in consensus. RESULTS: For the 240 calf segments scored for length, concordance with reference assessment was poorer for the time of flight than for either the bolus chase or time-resolved angiography (P = 0.0021 and P = 0.0082, respectively), and the latter two were statistically indistinguishable. For stenosis grading of the 461 calf and pedal segments, the time-resolved and bolus chase methods were superior to the time of flight (P = <0.0001 and P = 0.0041, respectively), and the contrast-enhanced methods were statistically indistinguishable. CONCLUSIONS: Both contrast-enhanced time-resolved and bolus chase MR angiography are superior to the time of flight in diagnosing distal station peripheral vascular disease.     

Carotid arteries: maximizing arterial to venous contrast in fluoroscopically triggered contrast-enhanced MR angiography with elliptic centric view ordering

PURPOSE: To obtain high-spatial-resolution, venous-suppressed, contrast material-enhanced, three-dimensional (3D) magnetic resonance (MR) angiograms of the carotid arteries and aortic arch by using an elliptic centric view ordering with MR fluoroscopic triggering. MATERIALS AND METHODS: Forty consecutive patients with cerebrovascular disease in the differential diagnosis were evaluated with fluoroscopically triggered 3D MR angiography (gadoteridol dose range, 0.1-0.3 mmol per kilogram of body weight; mean acquisition time, 40 second +/- 8 [SD]). The contrast-enhanced 3D MR angiograms were evaluated for overall quality, vascular signal intensity, venous suppression, and motion artifact. Twenty patients also underwent two-dimensional (2D) time-of-flight (TOF) MR angiography. The overall quality of the 2D TOF MR angiograms and comparative quality between the 2D TOF and contrast-enhanced 3D MR angiograms were determined. RESULTS: The contrast-enhanced 3D MR angiograms were of excellent or more than adequate quality for diagnosis in 36 of the 40 studies (90%). In 35 of the 38 contrast-enhanced 3D studies in which the contrast material bolus was detected fluoroscopically, the internal jugular vein signal intensity was either not detectable or barely visible. In 18 of the 20 patients who also underwent 2D TOF MR angiography, the quality of the contrast-enhanced 3D MR angiograms was graded as markedly superior or superior. CONCLUSION: Contrast-enhanced, elliptic centric 3D MR angiography with real-time MR fluoroscopic triggering offers high-spatial-resolution images of the carotid arteries and aortic arch with reliable venous suppression.