Calf Station Research Articles

Image Quality and Stenosis Assessment of Non-Contrast-Enhanced 3-T Magnetic Resonance Angiography in Patients with Peripheral Artery Disease Compared with Contrast-Enhanced Magnetic Resonance Angiography and Digital Subtraction Angiography.

PurposeTo evaluate the diagnostic performance of flow-sensitive dephasing (FSD)-prepared steady-state free precession (SSFP) magnetic resonance angiography (MRA) at 3 T for imaging infragenual arteries relative to contrast-enhanced MRA (CE-MRA) and digital subtraction angiography (DSA).Materials and MethodsA series of 16 consecutive patients with peripheral arterial disease (PAD) underwent a combined peripheral MRA protocol consisting of FSD-MRA for the calves and large field-of-view CE-MRA. DSA was performed on all patients within 1 week of the MR angiographies. Image quality and degree of stenosis was assessed by two readers with rich experience. Inter-observer agreement was determined using kappa statistics. Receiver operating characteristic (ROC) curve analysis determined the diagnostic value of FSD-MRA, CE-MRA, and CE-MRA combined with FSD-MRA (CE+FSD MRA) in predicting vascular stenosis.ResultsAt the calf station, no significantly difference of subjective image quality scores was found between FSD-MRA and CE-MRA. Inter-reader agreement was excellent for both FSD-MRA and CE-MRA. Both of FSD-MRA and CE-MRA carry a stenosis overestimation risk relative to DSA standard. With DSA as the reference standard, ROC curve analysis showed that the area under the curve was largest for CE+FSD MRA. The greatest sensitivity and specificity were obtained when a cut-off stenosis score of 2 was used.ConclusionIn patients with severe PAD,3 T FSD-MRA provides good-quality diagnostic images without a contrast agent and is a good supplement for CE-MRA. CE+FSD MRA can improve the accuracy of vascular stenosis diagnosis.

Fresh Blood Imaging using variable TR and variable refocusing flip angle for non-contrast peripheral MR angiography at 3T: a 7-Minute iliac to calf station run-offs scan

Fresh Blood Imaging using variable TR and variable refocusing flip angle for non-contrast peripheral MR angiography at 3T: a 7-Minute iliac to calf station run-offs scan

Improved receiver arrays and optimized parallel imaging accelerations applied to time-resolved 3D fluoroscopically tracked peripheral runoff CE-MRA

ObjectivesThree-station stepping-table time-resolved 3D contrast-enhanced magnetic resonance angiography has conflicting demands in the need to limit acquisition time in proximal stations to match the speed of the advancing contrast bolus and in the distal-most station to avoid venous contamination while still providing clinically useful spatial resolution. This work describes improved receiver coil arrays which address this issue by allowing increased acceleration factors, providing increased spatial resolution per unit time. Materials and methodsReceiver coil arrays were constructed for each station (pelvis, thigh, calf) and then integrated into a 48-element array for three-station peripheral CE-MRA. Coil element sizes and array configurations for these three stations were designed to improve SENSE-type parallel imaging taking advantage of an increase in coil count for all stations versus the previous 32 channel capability. At each station either acceleration apportionment or optimal CAIPIRINHA selection was used to choose the optimum acceleration parameters for each subject. Results were evaluated in both single- and multi-station studies. ResultsSingle-station studies showed that SENSE acceleration in the thigh station could be readily increased from R=8 to R=10, allowing reduction of the frame time from 2.5 to 2.1s to better image the typically rapidly advancing bolus at this station. Similarly, the improved coil array for the calf station permitted acceleration increase from R=8 to R=12, providing a 4.0 vs. 5.2s frame time. Results in three-station studies suggest an improved ability to track the contrast bolus in peripheral CE-MRA. ConclusionsModified receiver coil arrays and individualized parameter optimization have been used to provide improved acceleration at all stations in multi-station peripheral CE-MRA and provide high spatial resolution with frame times as short as 2.1s.

High-permittivity thin dielectric padding improves fresh blood imaging of femoral arteries at 3 T.

Fresh blood imaging (FBI) is a useful noncontrast magnetic resonance angiographic (MRA) method for the assessment of peripheral arterial disease, particularly for imaging patients with poor renal function. Compared with 1.5 T, 3 T enables higher signal-to-noise ratio and/or spatiotemporal resolution in FBI. Indeed, previous studies have reported successful FBI of the calf station at 3 T. However, FBI of the thigh station at 3 T has been reported to suffer from signal void in the common femoral artery of 1 thigh only because of the radial symmetry in transmit radiofrequency field (B1+) variation. We sought to increase the signal of femoral artery in FBI at 3 T using high-permittivity dielectric padding. We performed FBI and B1+ mapping of the thigh station at 3 T in 13 human subjects to compare the following 3 dielectric padding settings: no padding, commercially available thick (approximately 5 cm) dielectric padding, and high-permittivity thin (approximately 2 cm) dielectric padding. We characterized the radial symmetry in B1+ variation as well as its impact on the FBI signal at baseline and how dielectric padding improves B1+ and FBI. We evaluated the quality of 3 FBI MRA acquisitions using quantitative (ie, contrast-to-noise ratio of femoral arteries) and qualitative (ie, conspicuity of femoral arteries) analyses. With the subjects positioned on the magnetic resonance table in feet-first, supine orientation, the radial symmetry in B1+ variation attenuates the signal in the right common femoral artery. The signal void can be improved partially with commercial padding and improved further with high-permittivity padding. Averaging the results over the 13 subjects, the mean B1+, contrast-to-noise ratio, and conspicuity scores for the right common femoral artery were significantly higher with high-permittivity padding than with commercial padding and baseline (P < 0.001). Our study shows that high-permittivity dielectric padding can be used to increase the signal of femoral artery in FBI at 3 T.

Enhancement Characteristics and Impact on Image Quality of Two Gadolinium Chelates at Equimolar Doses for Time-Resolved 3-Tesla MR-Angiography of the Calf Station

PurposeTo compare enhancement characteristics and image quality of two macrocyclic gadolinium chelates, gadoterate meglumine and gadobutrol, in low-dose, time-resolved MRA of the calf station.Materials and Methods100 consecutive patients with peripheral arterial disease (stages II-IV) were retrospectively analysed. Fifty patients were included in each group - 32 men and 18 women for gadobutrol (mean age 67 years) and 34 men, 16 women for gadoterate meglumine (mean age 64 years). 0.03 mmol/kg bw of either gadobutrol or gadoterate meglumine was injected. Gadobutrol was diluted 1∶1 with normal saline (0.9% NaCl) to provide similar injection volume and bolus geometry compared to the undiluted 0.5 M dose of gadoterate meglumine. Signal-to-noise-ratio (SNR), contrast-to-noise-ratio (CNR) and image quality were analysed and compared between the two groups.ResultsMean SNR ranged from 83.0±46.7 (peroneal artery) to 96.4±64.5 (anterior tibial artery) for gadobutrol, and from 37.6±13.8 (peroneal artery) to 45.3±16.4 (anterior tibial artery) for the gadoterate meglumine group (p<0.0001). CNR values ranged from 30.1±20.1 (peroneal artery) to 37.6±26.0 (anterior tibial artery) for gadobutrol and from 14.9±8.0 (peroneal artery) to 18.6±16.4 (anterior tibial artery) for gadoterate meglumine (p<0.0001). No significant difference in image quality was found except for the peroneal arteries (p = 0.006 and p = 0.04). Interreader agreement was excellent (kappa 0.87–0.93)ConclusionThe significantly better enhancement as assessed by SNR and CNR provided by gadobutrol compared to gadoterate meglumine does not translate into substantial differences in image quality in an equimolar, low-dose, time-resolved MRA protocol of the calves.

Impact of Time-Resolved MRA on Diagnostic Accuracy in Patients With Symptomatic Peripheral Artery Disease of the Calf Station

The purpose of this article is to evaluate the added diagnostic accuracy of time-resolved MR angiography (MRA) of the calves compared with continuous-table-movement MRA in patients with symptomatic lower extremity peripheral artery disease (PAD) using digital subtraction angiography (DSA) correlation. Eighty-four consecutive patients with symptomatic PAD underwent a low-dose 3-T MRA protocol, consisting of continuous-table-movement MRA, acquired from the diaphragm to the calves, and an additional time-resolved MRA of the calves; 0.1 mmol/kg body weight (bw) of contrast material was used (0.07 mmol/kg bw for continuous-table-movement MRA and 0.03 mmol/kg bw for time-resolved MRA). Two radiologists rated image quality on a 4-point scale and stenosis degree on a 3-point scale. An additional assessment determined the degree of venous contamination and whether time-resolved MRA improved diagnostic confidence. The accuracy of stenosis gradation with continuous-table-movement and time-resolved MRA was compared with that of DSA as a correlation. Overall diagnostic accuracy was calculated for continuous-table-movement and time-resolved MRA. Median image quality was rated as good for 578 vessel segments with continuous-table-movement MRA and as excellent for 565 vessel segments with time-resolved MRA. Interreader agreement was excellent (κ = 0.80-0.84). Venous contamination interfered with diagnosis in more than 60% of continuous-table-movement MRA examinations. The degree of stenosis was assessed for 340 vessel segments. The diagnostic accuracies (continuous-table-movement MRA/time-resolved MRA) combined for the readers were obtained for the tibioperoneal trunk (84%/93%), anterior tibial (69%/87%), posterior tibial (85%/91%), and peroneal (67%/81%) arteries. The addition of time-resolved MRA improved diagnostic confidence in 69% of examinations. The addition of time-resolved MRA at the calf station improves diagnostic accuracy over continuous-table-movement MRA alone in symptomatic patients with PAD.

Nonenhanced ECG-gated quiescent-interval single shot MRA: Image quality and stenosis assessment at 3 tesla compared with contrast-enhanced MRA and digital subtraction angiography

To evaluate the diagnostic accuracy of a nonenhanced electrocardiograph-gated quiescent-interval single shot MR-angiography (QISS-MRA) at 3 Tesla with contrast-enhanced MRA (CE-MRA) and digital subtraction angiography (DSA) serving as reference standard. Following institutional review board approval, 16 consecutive patients with peripheral arterial disease underwent a combined peripheral MRA protocol consisting of a large field-of-view QISS-MRA, continuous table movement MRA, and an additional time-resolved MRA of the calves. DSA correlation was available in eight patients. Image quality and degree of stenosis was assessed. Sensitivity and specificity of QISS-MRA was evaluated with CE-MRA and DSA serving as the standards of reference and compared using the Fisher exact test. With the exception of the calf station, image quality with QISS-MRA was rated statistically significantly less than that of CE-MRA (P < 0.05, P = 0.17, and P = 0.6, respectively). A greater percentage of segments were not accessible with QISS-MRA (19.5-20.1%) in comparison to CE-MRA (10.9%). Relative to DSA, sensitivity for QISS-MRA was high (100% versus 91.2% for CE-MRA, P = 0.24) in the evaluated segments; however, specificity (76.5%) was substantially less than that of CE-MRA (94.6%, P = 0.003). Overall image quality and specificity of QISS-MRA at 3T are diminished relative to CE-MRA. However, when image quality is adequate, QISS-MRA has high sensitivity and, thus, has potential use in patients with contraindications to gadolinium.

Time‐resolved dual‐station calf–foot three‐dimensional bolus chase MR angiography with fluoroscopic tracking

To refine, adapt, and evaluate the technical aspects of fluoroscopic tracking for generating dual-station high-spatial-resolution MR angiograms of the calves and feet using a single injection of contrast material. Nine subjects (seven healthy volunteers followed by two patients) were imaged using a two-station calf-foot three-dimensional time-resolved bolus chase MR angiography protocol which provided <1.0 mm(3) spatial resolution throughout and 2.5- and 6.6-s frame times at the calf and foot stations, respectively. Real-time reconstruction of calf station time frames allowed visually guided triggering of table advance to the foot station. The studies were independently read and scored by two radiologists in six image quality categories. On average, overall diagnostic quality at the calf and foot stations was good-to-excellent, the calf arteries and all but the smallest foot arteries had good-to-excellent signal and sharpness, artifact and venous contamination were minor, and signal continuity across the inter-station interface was good. The feasibility of fluoroscopic tracking has been demonstrated as an efficient approach for high spatiotemporal imaging of the arteries of the calves and feet with good-to-excellent diagnostic quality and low degrading venous contamination.

3T versus 1.5T MR angiography in peripheral arterial occlusive disease: an equivalence trial in comparison with digital subtraction angiography

Summary Standardized single-injection 3-station moving-table 3T contrast-enhanced MR angiography (CE-MRA) is reliable for stenosis detection and classification in peripheral arterial occlusive disease with equivalent diagnostic performance as 1.5T CE-MRA, while contrast-to-noise ratio significantly increased at 3T for identical contrast dosage. Background Contrast-enhanced MR angiography (CE-MRA) has evolved into a reliable imaging technique for peripheral arterial occlusive disease (PAOD). Recent advances in MRI technology offer large homogeneous magnetic fields with comparable Field-of-Views at 3T and 1.5T, allowing visualization of the complete runoff vascular tree by single-injection 3-station (pelvic/thigh/calf) moving-table CE-MRA. Diagnostic performance of 3T versus 1.5T CE-MRA has not yet been described. The purpose of this study was to compare diagnostic accuracy of 3T CE-MRA in POAD in an equivalence trial with 1.5T CE-MRA, with conventional digital subtraction angiography (DSA) as the standard of reference. Methods In nineteen patients (13 men; mean age 69 years), DSA and standardized single-injection 3-station moving-table CE-MRA with equivalent acquisition protocols and contrast dosage were performed at 3T and 1.5T MRI (Philips, Best, the Netherlands). For CE-MRA, 0.2 mmol/kg body weight gadoterate meglumine was injected, with the first half of the bolus at 2 mL/s and second half at 0.6 mL/s. At 1.5T, a quadrature body coil (QBC) was used for imaging pelvic and thigh stations and a 4-element phased array coil for calf station. At 3T, a QBC was used in all three stations. DSA was performed using iomeprol injection at variable volumes and flow rates depending on the arterial segment. The arterial tree in each patient was divided into 27 segments, infrarenal aorta, common and external iliac arteries, common and superficial femoral arteries, popliteal arteries in thigh and calf station, tibiofibular trunk, proximal and distal halves of the anterior and posterior tibial arteries and peroneal arteries. Visual stenosis classification was performed in consensus by two radiologists in blinded manner using the following categories: class 1 (0%-stenosis), 2 (1-50%), 3 (51-75%), 4 (76-99%) and 5 (100%). Quantitative analysis of contrast-to-noise ratio (CNR) was performed for the external iliac artery and the superficial femoral artery. Results

Combined large field-of-view MRA and time-resolved MRA of the lower extremities: Impact of acquisition order on image quality

PurposeDifferent approaches exist for hybrid MRA of the calf station. So far, the order of the acquisition of the focused calf MRA and the large field-of-view MRA has not been scientifically evaluated. Therefore the aim of this study was to evaluate if the quality of the combined large field-of-view MRA (CTM MR angiography) and time-resolved MRA with stochastic interleaved trajectories (TWIST MRA) depends on the order of acquisition of the two contrast-enhanced studies. MethodsIn this retrospective study, 40 consecutive patients (mean age 68.1±8.7 years, 29 male/11 female) who had undergone an MR angiographic protocol that consisted of CTM-MRA (TR/TE, 2.4/1.0ms; 21° flip angle; isotropic resolution 1.2mm; gadolinium dose, 0.07mmol/kg) and TWIST-MRA (TR/TE 2.8/1.1; 20° flip angle; isotropic resolution 1.1mm; temporal resolution 5.5s, gadolinium dose, 0.03mmol/kg), were included. In the first group (group 1) TWIST-MRA of the calf station was performed 1–2min after CTM-MRA. In the second group (group 2) CTM-MRA was performed 1–2min after TWIST-MRA of the calf station. The image quality of CTM-MRA and TWIST-MRA were evaluated by 2 two independent radiologists in consensus according to a 4-point Likert-like rating scale assessing overall image quality on a segmental basis. Venous overlay was assessed per examination. ResultsIn the CTM-MRA, 1360 segments were included in the assessment of image quality. CTM-MRA was diagnostic in 95% (1289/1360) of segments. There was a significant difference (p<0.0001) between both groups with regard to the number of segments rated as excellent and moderate. The image quality was rated as excellent in group 1 in 80% (514/640 segments) and in group 2 in 67% (432/649), respectively (p<0.0001). In contrast, the image quality was rated as moderate in the first group in 5% (33/640) and in the second group in 19% (121/649) respectively (p<0.0001). The venous overlay was disturbing in 10% in group 1 and 20% in group 2 (p=n.s.). ConclusionIf a combined hybrid MRA approach with large field-of-view and time-resolved MRA is acquired the large field-of-view MRA should be acquired first in order for optimal image quality.

Peripheral MRA with continuous table movement: Imaging speed and robustness compared to a conventional stepping table technique

To investigate the potential of continuous table movement (CTM)-MRA for reduction of acquisition time and to evaluate the image quality in comparison to conventional stepping table (CST) MRA. The data of 82 patients were included in this retrospective, IRB-approved study. All patients underwent peripheral MRA at our institution. 41 consecutive patients were examined with a CST-MRA at a 1.5 T MR system. 41 different consecutive patients were examined with a CTM-MRA at 3.0 T MR system. Image quality was assessed by two independent radiologists in consensus on a 4-point Likert-type scale. Descriptive statistics and t-tests were used to compare image acquisition time of CST-MRA to that of CTM-MRA with and without additional time-resolved imaging of the feet using the TWIST technique. Additionally, acquisition time was compared in a subgroup of the fastest 50%. The mean imaging time for the CTM-MRA was 34% less than with the CST-MRA (18.2 min vs. 27.5 min; p<0.0001). Even with inclusion of the TWIST sequence the combined CTM-/TWIST-MRA protocol was 26% faster (20.3 min vs. 27.5 min; p<0.0001). The image quality was slightly better with CTM-MRA (CTM-MRA mean score 3.3±0.5, mean score CST-MRA 2.9±0.6). Venous overlay was significantly lower using the CTM-MRA approach (CTM-MRA mean score 2.8±0.4; CST-MRA mean score 2.2±0.7; p<0.0001). CTM-MRA is on average 30% faster than a comparable CST-MRA protocol with equal image quality. Even when adding an additional time-resolved-MRA of the calf station the CTM-MRA protocol is still 26% faster. In conclusion, this study proves that CTM-MRA further improves MRA by reducing user interference and image acquisition times and hence allowing to increase the clinical throughput.

Magnetic resonance angiography (MRA) of the calf station at 3.0 T: intraindividual comparison of non-enhanced ECG-gated flow-dependent MRA, continuous table movement MRA and time-resolved MRA

To compare 3D non-enhanced ECG-gated inflow-dependent MRA (NE-MRA) vs. continuous table movement (CTM) MR-angiography and time-resolved TWIST-MRA in the calf station at 3.0T in a clinical patient collective. 36 patients (27 male/9 female, 66.1 ± 14.4years) with PAOD (stage II-IV) underwent during a single MRI: NE-MRA, contrast-enhanced CTM-MRA and TWIST-MRA with a single dose of a gadolinium-based contrast agent. The image quality (IQ) and the degree of stenoses were rated on a four-point scale. Positive (PPV) and negative predictive values (NPV), sensitivity (SS) and specificity (SP) for stenoses detection were calculated for NE-MRA vs. CTM-MRA and vs. TWIST-MRA. Values were obtained for overall graduation of wall changes and for severe stenoses (>70%). With NE-MRA 122/288 segments were not assessable. Compared with CTM-MRA and TWIST-MRA the IQ was significantly inferior (p < 0.0001 to p = 0.0426). CTM-MRA/TWIST-MRA detected stenoses in 44.9%/46.1% of the segments, NE-MRA in 53.5%. SS/NPV of the NE-MRA ranged from 97.8 to 100%. The SP and PPV ranged from 72.7 to 85.5% and 66.7 to 78.2%. Contrast-enhanced MRA techniques are superior to NE-MRA regarding IQ and correct identification of stenoses. If technically successful, NE-MRA is characterised by high NPV and overestimation of the degree of stenoses.

Contrast-Enhanced Magnetic Resonance Angiography Following Subintimal Recanalization

To describe the appearance of lower extremity runoff vessels following subintimal recanalization (SIR) on contrast-enhanced magnetic resonance angiography (ceMRA) and compare 2 different ceMRA techniques. A total of 6 patients underwent stepping table 3-dimensional (3D) ceMRA and time-resolved 2-dimensional (2D) MRA within 1 to 3 days (mean 1.83 days) following SIR. The 2 techniques were compared with intra-arterial digital subtraction angiography (DSA). A total of 15 arteries were recanalized in 6 patients. Three-dimensional ceMRA allowed evaluation of patency in all segments above the knee. Postprocedural hyperemia impaired the assessment of the trifurcation vessels on 3D ceMRA. Due to its higher temporal resolution 2D MRA was not affected by venous contamination and allowed reliable confirmation of patency of the recanalized vessels. Diagnostic MRA studies of the lower extremity runoff vessels following SIR is possible, but a hybrid technique using a stepping table MR DSA and a time-resolved sequence like 2D MRA of the calf station is necessary for runoff assessment.

Peripheral Magnetic Resonance Angiography With Continuous Table Movement in Combination With High Spatial and Temporal Resolution Time-Resolved MRA With a Total Single Dose (0.1 mmol/kg) of Gadobutrol at 3.0 T

To prove the concept of peripheral continuous table movement (CTM) MR-angiography (MRA) in combination with high spatial and temporal resolution time-resolved TWIST-MRA in a single MR-examination at 3.0 T with a single dose (0.1 mmol/kg) of gadobutrol in total. We included 22 consecutive patients (15 m/7 f, mean age: 64 years) referred for peripheral MRA with clinical symptoms of peripheral arterial occlusive disease Fontaine stages II-IV. All of them underwent both CTM-MRA (TR: 2.4 ms/TE: 1.0 ms/flip angle: 21 degree) of the entire run-off vessels and TWIST-MRA (TR: 2.8 ms/TE: 1.1 ms/flip angle: 20 degree) of the calf station during a single MR-examination. All examinations were performed on a 3.0 T MR system (Tim Trio). Spatial resolution of the CTM-MRA datasets was technically limited to an acquired resolution of 1.2 x 1.2 x 1.96 mm3 reconstructed to 1.2 mm isotropic. The TWIST-MRA was acquired with 1.1 x 1.1 x 1.35 mm3 and reconstructed to 1.1 mm isotropic with a temporal resolution of 5.5 seconds in the calf station. A total of 0.1 mmol/kg BW gadobutrol diluted 1:1 with saline was injected at a flow rate of 1.5 mL/s of which 0.07 mmol/kg was administered for the CTM-MRA and 0.03 mmol/kg for the TWIST-MRA. CTM-MRA run off datasets were qualitatively assessed using a 4 point scale (4 = excellent, 1 = nondiagnostic) followed by TWIST-MRA datasets for the calf using the same scale. Additional relevant findings only visible in the TWIST-MRA were documented. All datasets could be evaluated with a total of 397 assessable segments. CTM-MRA was diagnostic in 99% (393/397 segments) with image quality judged as excellent in 54% (213/397 segments), good in 42% (14/397), and moderate in 4% (14/397) of analyzed segments respectively. Nondiagnostic image quality was seen in 1% (4/397 segments). Venous overlay in the calf station was found in 27% (6/22 patients). TWIST-MRA was diagnostic in 100% (115/115 segments), throughout with good or excellent image quality. In 14 of 22 patients additional relevant findings were detected by TWIST-MRA. Single-dose gadobutrol CTM-MRA in combination with a high spatial and temporal resolution TWIST-MRA at 3.0 T is a reliable technique with good image quality. Despite the use of single dose contrast agent large field of view coverage and dynamic images can be acquired. Because of its robustness, this imaging approach of the vasculature has great potential for a broad clinical use.

Peripheral Magnetic Resonance Angiography (MRA) With Continuous Table Movement at 3.0 T

To compare a standard step-by-step and a newly developed continuous table movement (CTM) technique for peripheral magnetic resonance angiography (MRA) at a 3.0-Tesla MR system equipped with a matrix coil system. We included 14 consecutive patients referred for peripheral MRA with clinical symptoms of peripheral arterial occlusive disease Fontaines stages II-IV. All of them underwent both step-by-step MRA and CTM-MRA in one session. Patients with impaired renal function (calculated glomerular filtration rate <30 mL/min) were not included. All examinations were performed on a 3.0-Tesla MR system. Maximal contrast agent volume was 31.5 mL (1.5 mL testbolus, 15 mL/MRA technique). For both techniques the same biphasic CA injection protocol was used, first 8 mL were injected at a flow rate of 1.5 mL/s directly followed by 7 mL at 0.8 mL/s again followed by 25 mL of saline also at 0.8 mL/s. Spatial resolution of the CTM-MRA datasets was technically limited to 1.2 mm(3), step-by-step MRA reached 1.4 x 1.1 x 1.2 mm(3) in the abdominal station, 0.9 x 0.9 x 0.9 mm(3) in the most distal calf station. First CTM-MRA datasets were read and findings thereafter correlated with the step-by-step MRA datasets. Examination time of both examinations were recorded and compared. All datasets could be evaluated. The first 4 CTM-MRA cases were limited by incorrect timing in the most distal vessels obscuring distinct atherosclerotic changes of those vessels. Because of the absence of multiple localizers and subtraction masks examination time was considerably shorter when using the CTM-MRA technique. Relevant findings that were detected by the step-by-step MRA were also detected by CTM-MRA. MRA with CTM is an easy applicable technique for imaging peripheral vessels without the need for planning different steps and field of view positioning, thereby reducing examination time considerably. However, the slightly reduced spatial resolution compared with standard step-by-step MRA is a drawback especially in the most distal calf vessels.

Hybrid contrast-enhanced MR angiography of pelvic and lower extremity vasculature at 3.0 T: Initial experience

Purpose The objective of this study was to describe contrast-enhanced magnetic resonance angiography (MRA) of the lower extremities at 3.0 T system for assessment of high resolution images in patients with peripheral arterial occlusive disease (PAOD). Material and methods 21 Patients with suspected PAOD were examined with four-station MRA at a 3.0 T MR system. The MRA protocol consisted of a hybrid technique with two contrast media injections, the first one for visualization of the calf and foot vasculature (non-moving-table technique), the second one for imaging the aortoiliacal and femoral arteries (moving-table technique). For the femoropopliteal and calf station a randomly segmented central k-space ordering (contrast-enhanced timing-robust angiography [CENTRA]) was used. MR-images were analyzed independently by two radiologists with regard to image quality, venous overlap and grade of stenosis. In 6 patients digital subtraction angiography was performed within the following 7 days and evaluated by two radiologists in consensus with regard to the grade of stenosis. The vasculature-tree of each leg was divided in 12 segments, and 3 anatomical regions (iliacal, femoropopliteal, calf/foot). Results 490 and 488 of 495 arterial segments were visualized with diagnostic image quality by observer 1 and observer 2, respectively. Image quality was excellent in 470 and 457 arterial segments, respectively. Only 4 segments were rendered as non-diagnostic due to venous overlap. Relevant arterial stenoses (50–99%) were detected in 43 and 47 segments by observer 1 and observer 2, 66 and 65 arterial segments, respectively, were interpreted as occluded. Conclusion The hybrid MRA protocol at 3.0 T offers high diagnostic quality for the whole peripheral arterial tree without venous contamination at high spatial resolution.

Peripheral Magnetic Resonance Angiography with a Multi-Compartment Curved Leg Wrap for Thigh Compression

A curved urethane rf-welded leg wrap with multi-compartment inflation was developed for optimal thigh compression to suppress venous enhancement during peripheral magnetic resonance angiography (MRA). In 49 patients with suspected peripheral vascular disease, bilateral thigh leg wraps were inflated to 60 mm Hg just prior to mask imaging of 3D bolus chase peripheral MRA at 1.5 T using 45 mL gadolinium contrast agent. The time from contrast arrival in the abdominal aorta to venous enhancement in the calf was measured by repeating the calf station at approximately 30 second intervals until venous contamination was observed. The mean time to venous enhancement with thigh compression was 108 +/- 35 s, ranging from 40 to 181 s. In 64 out of 98 legs (65%), veins did not enhance even after repeating the calf station 3 times. In 10 legs (10%), venous enhancement was identified on the first phase of the calf station including 2 legs with cellulitis. However, the enhancing veins tended to be superficial and did not substantially interfere with visualization of calf arteries. This preliminary experience with a curved multi-compartment leg wrap for thigh compression shows high quality MRA with a long window of arterial enhancement and a minimum of venous contamination.

Comparison of Multistation MR Angiography with Integrated Parallel Acquisition Technique versus Conventional Technique with a Dedicated Phased-array Coil System in Peripheral Vascular Disease

To assess the impact of integrated parallel acquisition technique (iPAT) on signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), venous contamination, and overall image interpretability for peripheral magnetic resonance (MR) angiography with use of a dedicated phased-array coil system. Three-dimensional contrast material-enhanced conventional MR angiography and iPAT peripheral MR angiography was performed at three stations (pelvis, thigh, calf) in 38 consecutive patients on a 1.5-T high-performance cardiovascular system (conventional MR angiography, n=19; iPAT MR angiography, n=19). A total of 29 vessel segments per patient were analyzed. For each segment, arterial, muscle, and background signal were measured; SNR and CNR were calculated; and repeated-measures analysis of variance was performed. For each of the three stations, the degree of venous contamination and the overall confidence of interpretability were analyzed with use of ordinal logistic regression analysis accounting for correlated outcome data. A total of 1,018 vessel segments were available for analysis (477 with conventional MR angiography, 541 with iPAT MR angiography). Compared with conventional MR angiography, iPAT MR angiography resulted in decreased SNR and CNR in the pelvis and thigh stations but no change in the calf station. The difference in the pelvis was statistically significant (P<.007 for SNR and P<0.01 for CNR). Venous contamination in the calf station was significantly less on iPAT MR angiography (P<.003), with no significant differences in the other stations. The overall confidence of interpretability with iPAT MR angiography was significantly better on the lower station (P<.008). iPAT MR angiography leads to reduced SNR and CNR in the pelvis and thigh, but this does not affect interpretability of images obtained at these stations. The temporal gain results in significantly increased interpretability as a result of less venous contamination in the calf station. iPAT MR angiography is superior to conventional MR angiography for peripheral imaging.

Lower Extremity: Low-Dose Contrast Agent Intraarterial MR Angiography in Patients—Initial Results

Institutional review board approval and patient consent were obtained. A low-dose injection protocol for intraarterial three-dimensional (3D) gadolinium-enhanced magnetic resonance (MR) angiography was derived from femoral flow phantom studies and prospectively evaluated in patients with peripheral arterial occlusive disease (PAOD). All MR angiograms were obtained at 1.5 T with a T1-weighted gradient-echo sequence. MR angiograms of a gadolinium dilution series (0.8-200.0 mmol/L) were acquired in a femoral phantom at different flow rates. Signal-to-noise ratios (SNRs) above the 75% threshold of the measured maximum were considered optimal. The lowest optimal concentration was injected intraarterially in nine patients to obtain 3D MR angiograms of the thigh and calf station. Contrast-to-noise ratios (CNRs) were calculated for four arterial segments. The low optimal concentration of 50 mmol/L (20-mL bolus volume), about 5% of the total permissible dose, showed SNRs larger than the 75% threshold in the phantom study. In patients, this concentration led to high-spatial-resolution angiograms with mean CNRs of 70.0 +/- 14.5 (+/- standard deviation) for the superficial femoral artery and 47.5 +/- 13.4 at the infrapopliteal level. Low-dose contrast agent intraarterial 3D MR angiography showed high arterial enhancement, enabling assessment of lower extremity arteries in patients with PAOD and multiple injections--a crucial precondition for MR-guided endovascular interventions.

Decreased venous contamination on 3D gadolinium-enhanced bolus chase peripheral mr angiography using thigh compression.

We evaluated the potential for improving bolus chase peripheral MR angiography in patients with fast arterial flow using thigh compression to prevent venous contamination. We performed bolus chase peripheral MR angiography in 32 consecutive patients in whom the travel time for a contrast agent to reach the popliteal artery trifurcation was less than 25 sec. Thigh compression was applied by a tourniquet (n = 13) or blood pressure cuff inflated to 60 mm Hg (n = 19). We compared the results with those of 36 consecutive patients who underwent angiography without thigh compression. The effect of thigh compression on arterial flow and tissue enhancement was assessed in patients with symmetric travel time in both legs by applying compression to one leg during the time-resolved 2D-projection MR angiography with 6 mL of gadolinium. On 3D bolus chase MR angiography, thigh compression was applied bilaterally. Venous contamination on the 3D images of the calf was graded as 0, none; 1, trace; 2, mild; 3, moderate; and 4, severe. Signal-to-noise ratio was measured in the popliteal artery. Thigh compression slowed the arterial travel time by a mean +/- SD of 4.7 +/- 2 sec (p < 0.001) with a blood pressure cuff and 3.1 +/- 1 sec (p < 0.001) with a tourniquet. Blood pressure cuffs reduced the score of venous contamination on the calf station from 1.9 to 0.4 (p < 0.05) for intermediate flow (contrast travel time, 20-25 sec) and from 2.5 to 0.9 (p < 0.05) for fast flow (< 20 sec). Thigh compression increased the popliteal artery signal-to-noise ratio (81 vs 52, p < 0.001). Thigh compression with blood pressure cuffs inflated to 60 mm Hg slows down arterial flow, increases arterial signal-to-noise ratio, and reduces venous contamination on 3D gadolinium-enhanced bolus chase peripheral MR angiography.