Unenhanced MR Angiography Research Articles

Diagnostic performance of 3.0 T unenhanced Dixon water-fat separation coronary MR angiography in patients with low-to-intermediate risk of coronary artery disease

PurposeTo evaluate the diagnostic performance of 3.0 T unenhanced compressed-sensing sensitivity encoding (CS-SENSE) Dixon water-fat separation coronary MR angiography (CMRA) in patients with low-to-intermediate risk of coronary artery disease (CAD) and its ability to grade the severity of CAD based on Coronary Artery Disease Reporting and Data System (CAD-RADS). MethodsA total of 55 patients who was clinically evaluated as low-to-intermediate risk of CAD were finally included to undergo both 3.0 T CS-SENSE water-fat separation CMRA and coronary computed tomography angiography (CCTA), and 11 of them also underwent X-ray coronary angiography (CAG). The severity of coronary artery disease was graded in patients who had completed both CCTA and CMRA examinations by the use of CAD-RADS reports for the patients with stable chest pain, and the diagnostic consistency between the two approaches was evaluated. Diagnostic performance of CMRA was assessed using the combination of CCTA and CAG as the reference standard for excluding or confirming CAD respectively. ResultsThe sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and diagnostic accuracy of 3.0 T unenhanced water-fat separation coronary MRA were 90.0%, 95.0%, 81.8%, 97.4% and 94.0% for a patient-based analysis respectively. In comparison with CCTA, 3.0 T Dixon water-fat separation CMRA demonstrated excellent consistency in grading the severity of coronary heart disease according to CAD-RADS (0.77 for kappa value). ConclusionIn the group of low-to-intermediate probability for CAD, 3.0 T unenhanced CS-SENSE Dixon water-fat separation CMRA can present satisfactory diagnostic performance for the exclusion of CAD with high sensitivity and negative predictive value as well as the evaluation of grading the severity of coronary artery disease.

Effects of Tissue Relaxation, Eddy currents, and Acceleration on Velocity-Selective Preparation Pulses

Fourier-transform-based velocity-selective (FT-VS) magnetization preparation has shown great promise for unenhanced MR angiography and arterial spin labeling. Although recent technical advances made FT-VS preparation resistant to B0 and B1 field inhomogeneity, there remain other non-ideal conditions including tissue relaxation, eddy currents, and accelerated motion, which are often ignored during excitation pulse design. In this study, using a double-refocused VS preparation pulse as a testbed, excitation profiles were numerically simulated taking into account the potential effects of the three non-ideal conditions. The longitudinal magnetization of arterial blood resulting from FT-VS preparation turned out to decrease from the ideal value of MSUB0/SUB to 0.92MSUB0/SUB, 0.99MSUB0/SUB, and 0.88MSUB0/SUB due to tissue relaxation, eddy currents, and accelerated motion, respectively. When all three factors were considered simultaneously, the worst-case relative contrast ratio (CR) between arterial blood and muscle tissue was estimated as 0.86, corresponding to a decrease by 14 % from the ideal CR of 1.0.

Use of Non-Contrast-Enhanced MR Angiography to Assess Recanalization after Uterine Artery Embolization

The purpose of this study was to examine the use of non-contrast-enhanced MR angiography (MRA) for assessing recanalization of uterine arteries (UAs) after uterine artery embolization (UAE) for symptomatic fibroids. Pre-procedural and follow-up unenhanced MRA images of 30 patients were reviewed, and the extent to which the UAs could be visualized was classified on a 4-point scale. An increase in the score between consecutive time points indicates that a previously inconspicuous segment of the UA became visible on follow-up images. Patients were divided into two groups according to the presence (or absence) of recanalization. The median UA visualization score at each follow-up was significantly lower than that at baseline (p < 0.01), but there was no significant difference between the scores of the follow-up images. Recanalization was detected in 63% (19/30) of patients. In these patients, the mean decrease in uterine and largest fibroid volume at 12 months after UAE was inferior to the mean decrease in patients for whom recanalization was not detected. Based on MRA assessment, recanalization after UAE occurred in 63% of patients but did not compromise the reduction in uterine and dominant fibroid volumes within 12 months after UAE.

Non-contrast MRI protocol for TAVI guidance: quiescent-interval single-shot angiography in comparison with contrast-enhanced CT

ObjectivesTo prospectively compare unenhanced quiescent-interval single-shot MR angiography (QISS-MRA) with contrast-enhanced computed tomography angiography (CTA) for contrast-free guidance in transcatheter aortic valve intervention (TAVI).MethodsTwenty-six patients (mean age 83 ± 5 years, 15 female [58%]) referred for TAVI evaluation underwent QISS-MRA for aortoiliofemoral access guidance and non-contrast three-dimensional (3D) “whole heart” MRI for prosthesis sizing on a 1.5-T system. Contrast-enhanced CTA was performed as imaging gold standard for TAVI planning. Image quality was assessed by a 4-point Likert scale; continuous MRA and CTA measurements were compared with regression and Bland-Altman analyses.ResultsQISS-MRA and CTA-based measurements of aortoiliofemoral vessel diameters correlated moderately to very strong (r = 0.572 to 0.851, all p ≤ 0.002) with good to excellent inter-observer reliability (intra-class correlation coefficient (ICC) = 0.862 to 0.999, all p < 0.0001) regarding QISS assessment. Mean diameters of the infrarenal aorta and iliofemoral vessels differed significantly (bias 0.37 to 0.98 mm, p = 0.041 to < 0.0001) between the two modalities. However, inter-method decision for transfemoral access route was comparable (κ = 0.866, p < 0.0001). Aortic root parameters assessed by 3D whole heart MRI strongly correlated (r = 0.679 to 0.887, all p ≤ 0.0001) to CTA measurements.ConclusionQISS-MRA provides contrast-free access route evaluation in TAVI patients with moderate to strong correlations compared with CTA and substantial inter-observer agreement. Despite some significant differences in minimal vessel diameters, inter-method agreement for transfemoral accessibility is strong. Combination with 3D whole heart MRI facilitates unenhanced TAVI guidance.Key Points• QISS-MRA and CTA inter-method agreement for transfemoral approach is strong.• QISS-MRA is a very good alternative to CTA and MRA especially in patients with Kidney Disease Outcomes Quality Initiativestages 4 and 5.• Combination of QISS-MRA and 3D “whole heart” MRI facilitates fully unenhanced TAVI guidance.

Multi-observer comparison study between unenhanced quiescent-interval single-shot magnetic resonance angiography and invasive carbon dioxide angiography in patients with peripheral arterial disease and chronic renal insufficiency

ObjectivesNon-contrast-enhanced quiescent-interval single-shot magnetic resonance angiography (QISS-MRA) and invasive carbon dioxide (CO2) angiography are suggested as nephroprotective methods for accurate staging of peripheral arterial disease (PAD) in patients with chronic renal insufficiency (CRI). The aim of our study was to compare the image quality of both examinations. Methods16 consecutive PAD patients with highly impaired renal function (estimated glomerular filtration rate (eGFR) < 30 ml/min/1.73 m²) who underwent 3 T MRA with QISS and catheter angiography with CO2 within 90 days were retrospectively included. Subjective image quality was determined using a five-point Likert scale (1, non-diagnostic; 5, excellent) and presence of significant (≥50%) stenoses of pelvic and lower extremity arteries (21-segment-model) was evaluated per-region and per-segment, respectively, in random order by four independent readers with different levels of experience. CO2 angiography of an experienced interventional radiologist was considered the standard reference method. Results167 segments were available for direct comparison with a prevalence of ≥50% stenoses of 28.1%. QISS-MRA yield was: sensitivity 91.5%, specificity 94.2%, positive predictive value 86.0% and negative predictive value 96.6%, with an intraclass correlation coeffcient (ICC) of 0.88. Median values of qualitative imaging parameters for QISS-MRA were as follows: arterial signal intensity: 4 (pelvis), 5 (thigh), 5 (calf); venous overlay: 4, 5, 5; susceptibility artifacts: 5, 5, 5; motion artifacts: 4, 5, 5; ECG-related artifacts: 5, 5, 5. ICC-values for image quality were 0.74, 0.73, 0.93, 0.69 and 0.79, respectively. Arterial opacification at CO2 angiography was rated 3, 4, 3, with an ICC of 0.63. ConclusionsImage quality of non-invasive unenhanced MR angiography with QISS was preferred over invasive CO2 angiography, whilst taking into account that it offers high diagnostic performance for the detection and ruling out of PAD.

Characterization and suppression of stripe artifact in velocity-selective magnetization-prepared unenhanced MR angiography.

To characterize and suppress stripe artifact associated with velocity-selective (VS) magnetization for unenhanced MRA. Extended phase graph formalism was used to show that the stripe artifact contains multiples of the fundamental frequency that is determined by the area of unipolar VS gradient. Four VS preparation pulses whose excitation profiles are spatially shifted by quarter the fundamental period of the stripes, were applied alternately. For further suppression of the artifact, k-space data at kz = 0 were averaged over the 4 VS preparations. The proposed schemes were tested in a chicken breast phantom and healthy human subjects. When the standard VS preparation scheme was used, stripe artifact was shown in all the reconstructed images and appeared as artifactual peaks in k-space that corresponded to the first and second order harmonics of the fundamental frequency. Alternate application of the 4 phase-shifted VS preparation pulses suppressed the stripes, but not completely, as evidenced by residual erroneous peaks in k-space. After the k-space averaging, the stripe artifact was nearly eliminated. Stripe artifact in VS-MRA consists of multiples of the fundamental frequency and can be effectively suppressed through alternate application of phase-shifted VS preparations along with k-space averaging.

Unenhanced and Contrast-Enhanced MR Angiography and Perfusion Imaging for Suspected Pulmonary Thromboembolism.

This article discusses the basics of unenhanced MR angiography (MRA) and MR venography (MRV), time-resolved contrast-enhanced (CE) MRA and dynamic first-pass CE perfusion MRI, and unenhanced and CE MRV, in addition to assessing the clinical relevance of these techniques for evaluating patients with suspected pulmonary thromboembolism and deep venous thrombosis. Since the 1990s, the efficacy of MRA or MRV and dynamic perfusion MRI for patients with suspected pulmonary thromboembolism and deep venous thrombosis has been evaluated. On the basis of the results of single-center trials, comprehensive MRI protocols, including pulmonary unenhanced and CE MRA, perfusion MRI, and MRV, promise to be safe and time effective for assessing patients with suspected pulmonary thromboembolism, although future multicenter trials are required to assess the real clinical value of MRI.

Unenhanced 3D turbo spin echo MR angiography of lower extremity arteries: comparison with 128-MDCT angiography.

This study aimed to investigate the feasibility and diagnostic power of unenhanced 3D turbo spin echo MR angiography sequence (a technique based on subtraction of corresponding images acquired in diastole and systole, Syngo Native Space-Siemens healthcare) to identify peripheral artery disease (PAD). Thirty patients (619 arterial segments in total) suspected with PAD and who were assessed with lower extremity MDCT angiography were examined starting from the level of aortic bifurcation for both lower extremities by 3D native space MR angiography. Two readers assessed the image quality of native space MR angiography and number of lesions, their degrees of stenosis and localizations. The differences and compliance between the readers in the parameters assessed were investigated. Out of 619 segments; Reader 1 considered 187 segments (30.2%) and Reader 2 considered 177 segments (28.6%) to have poor and inadequate MR image quality. When compared to CTA, sensitivity, specificity and diagnostic accuracy of native space MR angiography were calculated as 81.0, 83.1, 82.6%, respectively, by Reader 1, while the same parameters were calculated as 69.9, 92.6, 84.9%, respectively, by Reader 2. When the two readers were examined together, sensitivity, specificity, diagnostic accuracy were found to be 76.3, 88.1, 83.7%, respectively, and the positive predictive value and negative predictive value was 70.3 and 89.9%, respectively. A significantly better image quality was acquired with the age group below 50years (p=0.002). Native space MR angiography technique can be used as the first-step imaging technique before contrast-enhanced examinations in young and middle age patients with suspected PAD and for patients with the risk of nephrogenic systemic fibrosis in chronic renal failure.

Hemodynamic analysis of renal artery stenosis using computational fluid dynamics technology based on unenhanced steady-state free precession magnetic resonance angiography: preliminary results

This study aims to evaluate the feasibility of computational fluid dynamics (CFD) technology in analysis of renal artery stenosis (RAS) based on unenhanced MR angiography (MRA). Thirty hypertensive patients with unilateral RAS, and 10 normal volunteers, underwent unenhanced MRA on a 1.5 T MR scanner. 12 of 30 patients also underwent ultrasound (US) to detect peak systolic velocity. The patient-specific CFD based on MRA was carried out thereafter. Stenosis grades and hemodynamic variables at the stenosis of main renal artery, including pressure difference (PD), velocity and mass flow rate (MFR), were analysed. And the hemodynamic indices of stenoses were compared with the parameters of normal renal arteries and available US velocity profile. High intraclass correlation coefficient (value 0.995) and no significant difference (p > 0.05) was shown between maximum velocity of CFD and peak systolic velocity of US in 12 patients. For normal renal arteries, the average PD, velocity and MFR were all in the reported normal physiological range. However, for stenotic arteries, the translesional PD and velocity of main renal arteries increased with the severity of stenotic degrees, while the MFR decreased. 50 % diameter stenosis was the threshold at which all three hemodynamic parameters experienced significant changes (p < 0.01). This preliminary study shows that unenhanced-MRA-based CFD can be utilized to noninvasively analyse hemodynamic parameters of RAS. The acquired variables may provide meaningful information regarding stratification of the stenosis and further therapeutic treatment.

State-of-the-art aortic imaging: Part I - fundamentals and perspectives of CT and MRI

Over the last two decades, imaging of the aorta has undergone a clinically relevant change. As part of the change non-invasive imaging techniques have replaced invasive intra-arterial digital subtraction angiography as the former imaging gold standard for aortic diseases. Computed tomography (CT) and magnetic resonance imaging (MRI) constitute the backbone of pre- and postoperative aortic imaging because they allow for imaging of the entire aorta and its branches. The first part of this review article describes the imaging principles of CT and MRI with regard to aortic disease, shows how both technologies can be applied in every day clinical practice, offering exciting perspectives. Recent CT scanner generations deliver excellent image quality with a high spatial and temporal resolution. Technical developments have resulted in CT scan performed within a few seconds for the entire aorta. Therefore, CT angiography (CTA) is the imaging technology of choice for evaluating acute aortic syndromes, for diagnosis of most aortic pathologies, preoperative planning and postoperative follow-up after endovascular aortic repair. However, radiation dose and the risk of contrast induced nephropathy are major downsides of CTA. Optimisation of scan protocols and contrast media administration can help to reduce the required radiation dose and contrast media. MR angiography (MRA) is an excellent alternative to CTA for both diagnosis of aortic pathologies and postoperative follow-up. The lack of radiation is particularly beneficial for younger patients. A potential side effect of gadolinium contrast agents is nephrogenic systemic fibrosis (NSF). In patients with high risk of NSF unenhanced MRA can be performed with both ECG- and breath-gating techniques. Additionally, MRI provides the possibility to visualise and measure both dynamic and flow information.

Unenhanced 3D Turbo Spin-Echo MR Angiography of Lower Limbs in Peripheral Arterial Disease: A Comparative Study With Gadolinium-Enhanced MR Angiography

The purpose of this study was to assess the feasibility and diagnostic performance of an unenhanced MR angiography sequence (Syngo Native Space, Siemens Healthcare) to detect and quantify lower-limb peripheral arterial disease (PAD), with gadolinium-enhanced MR angiography (CE-MRA) as the reference standard. Fifty-one patients known to have lower-limb arteriopathy were included in this prospective study. For every patient, we performed Native sequence and CE-MRA on a 1.5-T system. We evaluated examination duration, image quality, and location, number, and severity of lesions. Examination duration was longer for Native sequence (mean, 39.6 min, vs 10 min for CE-MRA). Image quality was significantly better for CE-MRA, with 92% of images listed as good to excellent for CE-MRA, compared to 53% for Native. Sensitivity, specificity, negative predictive value (NPV), and accuracy of Native were respectively 75%, 95%, 89%, and 88% for all mixed levels; 52%, 97%, 88%, and 87% for aortoiliac level; 87%, 99%, 95%, and 92% for femoropopliteal level; and 82%, 87%, 87%, and 85% for subpopliteal level. If we considered only patients with Leriche and Fontaine stage II arteriopathy, Native results were slightly better, with respective specificities and NPVs of 96% and 91% for all mixed levels; 98% and 90% for aortoiliac level; 98% and 93% for femoropopliteal level; and 91% and 90% for subpopliteal level. Unenhanced MR angiography, cheaper than CE-MRA, showed in our study a good NPV, which suggests its utility as first-line test to screen for PAD, especially in patients at risk of nephrogenic systemic fibrosis.

Evaluation of Renal Artery in Hypertensive Patients by Unenhanced MR Angiography Using Spatial Labeling With Multiple Inversion Pulses Sequence and by CT Angiography

The purposes of this study were to determine the performance of a new unenhanced MR angiography (MRA) sequence, spatial labeling with multiple inversion pulses (SLEEK), with regard to its ability to present the renal arteries and to reveal renal artery disease in patients with secondary hypertension. Unenhanced MRA using SLEEK was performed on a 1.5-T MRI system for assessing renal arteries in 50 patients with hypertension. Then all patients underwent CT angiography (CTA) within 1-7 days. The ability to present the renal arteries and to reveal renal artery disease with SLEEK was evaluated by two experienced radiologists and was compared with CTA results using a joint reading performed in consensus. Forty-six patients with hypertension successfully underwent SLEEK MRA. A total of 119 renal arteries were assessed, including 86 normal arteries, 26 with stenoses, and seven with fibromuscular dysplasia on CTA. There was excellent correlation between SLEEK and CTA in presenting the degree of renal artery stenosis (r(s) = 0.851; p < 0.05). SLEEK was superior to CTA in revealing the third- and fourth-order segmental branches in the renal parenchyma (p < 0.05). SLEEK has the advantage of avoiding interference from vertebra, atherosclerotic plaques, and early venous system enhancement. Unenhanced MRA using SLEEK is a reliable diagnostic method for evaluating renal artery disease and revealing segmental branches in the renal parenchyma. It is relatively inexpensive and is not associated with renal complications. It can be used as an alternative to CTA for screening for renal artery disease, especially in patients with hypertension and renal insufficiency.

Unenhanced MR Angiography of Renal Arteries: 51 Patients

The purpose of this research was to assess the feasibility and performance of an unenhanced 3D balanced steady-state free precession (SSFP) sequence, compared with contrast-enhanced MR angiography (CEMRA), which is the reference standard to detect and quantify renal artery stenoses (RAS). Fifty-one patients were included in this prospective study. Balanced SSFP sequence (Native) and CEMRA were performed using a 1.5-T magnet. Signal quality and stenosis grade were assessed per segment for renal arteries and for ostia of celiac trunk and superior mesenteric artery (SMA). We compared signal quality of Native and CEMRA. Sensitivity, specificity, negative predictive value (NPV), and accuracy were also calculated. Evaluation involved 114 renal arteries, 51 celiac trunks, and 51 SMAs. By use of CEMRA, 20 significant stenoses were found for renal arteries, 10 stenoses and three occlusions for celiac trunk, and three stenoses for SMA. At artery-by-artery analysis, sensitivity, specificity, accuracy, and NPV of the balanced SSFP sequence in detecting stenosis were respectively 85%, 96%, 94%, and 96% for renal arteries; 100%, 97%, 98%, and 100% for celiac trunk; and 100%, 100%, 100%, and 100% for SMA. No significant difference of signal quality was found for the entire examination and for the different segments evaluated except for hilar and intrarenal branches, which showed better signal quality on balanced SSFP sequence. The NPV results in our study suggest that unenhanced balanced SSFP MR angiography can be the first-choice imaging method to exclude RAS in patients at high risk of nephrogenic systemic fibrosis. However, when stenosis is found, other imaging modalities are necessary for better estimation.

First-pass contrast-enhanced renal MRA at 7 Tesla: initial results

The aim of this study was to assess the feasibility of first-pass contrast-enhanced renal MR angiography (MRA) at 7 T. In vivo first-pass contrast-enhanced high-field examinations were obtained in eight healthy subjects on a 7-T whole-body MRI. A custom-built body transmit/receive radiofrequency (RF) coil and RF system suitable for RF shimming were used for image acquisition. For dynamic imaging, gadobutrol was injected intravenously and coronal unenhanced, arterial and venous data sets using a T1-weighted spoiled gradient-echo sequence were obtained. Qualitative image analysis and assessment of artefact impairment were performed by two senior radiologists using a five-point scale (5 = excellent, 1 = non-diagnostic). SNR and CNR of the perirenal abdominal aorta and both main renal arteries were assessed. Qualitative image evaluation revealed overall high-quality delineation of all assessed segments of the unenhanced arterial vasculature (meanunenhanced 4.13). Nevertheless, the application of contrast agent revealed an improvement in vessel delineation of all the vessel segments assessed, confirmed by qualitative (meanunenhanced 4.13 to meancontrast-enhanced 4.85) and quantitative analysis (SNR meanunenhanced 64.3 to meancontrast-enhanced 98.4). This study demonstrates the feasibility and current constraints of ultra-high-field contrast-enhanced renal MRA relative to unenhanced MRA.

Peripheral Arterial Disease in a Symptomatic Diabetic Population: Prospective Comparison of Rapid Unenhanced MR Angiography (MRA) With Contrast-Enhanced MRA

The joint guidelines of the American College of Cardiology and American Heart Association support the use of contrast-enhanced MR angiography (CEMRA) to diagnose the location and degree of stenosis in patients with known or suspected peripheral arterial disease (PAD). The high prevalence of chronic renal impairment in diabetic patients with PAD and the need for high doses of gadolinium-based contrast agents place them at risk for nephrogenic systemic fibrosis. The purpose of our study was to evaluate the accuracy of the rapid technique of quiescent-interval single-shot (QISS) unenhanced MR angiography (MRA) compared with CEMRA for the diagnosis in diabetic patients referred with symptomatic chronic PAD. This prospective two-center study evaluated 25 consecutive diabetic patients with documented or suspected symptomatic PAD. Both centers used identical imaging protocols. Images were independently analyzed by two radiologists. A subgroup analysis was performed of patients who were also assessed with digital subtraction angiography (DSA) as part of the standard-of-care protocol before revascularization. For this study, 775 segments were analyzed. On a per-segment basis, the mean values of the diagnostic accuracy of unenhanced MRA compared with reference CEMRA for two reviewers, reviewers 1 and 2, were as follows: sensitivity, 87.4% and 92.1%; specificity, 96.8% and 96.0%; positive predictive value, 90.8% and 94.0%; and negative predictive value, 95.5% and 94.6%. Substantial agreement was found when overall DSA results were compared with QISS unenhanced MRA (κ = 0.68) and CEMRA (κ = 0.63) in the subgroup of patients who also underwent DSA. There was almost perfect agreement between the two readers for stenosis scores, with Cohen's kappa values being greater than 0.80 for both MRA techniques. The results of our study indicate that QISS unenhanced MRA is an accurate noncontrast alternative to CEMRA for showing clinically significant arterial disease in patients with diabetes with symptomatic PAD.

Preoperative evaluation of neurovascular relationship by using contrast-enhanced and unenhanced 3D time-of-flight MR angiography in patients with trigeminal neuralgia

Microvascular decompression is an etiological strategy for the therapy of trigeminal neuralgia (TN). Preoperative identification of neurovascular compression, therefore, could have an impact on the determination of appropriate treatment for TN. To evaluate the value of contrast-enhanced and unenhanced three-dimensional (3D) time-of-flight (TOF) MR angiography in the visualization of neurovascular relationship in patients with TN. Thirty-seven patients with unilateral TN underwent unenhanced and contrast-enhanced 3D TOF MR angiography with a 3.0-T MR system. Images were reviewed by a radiologist blinded to clinical details. Vascular contact with the trigeminal nerve was identified, and the nature of the involved vessels (artery or vein) was determined. All patients underwent microvascular decompression. In 37 patients with TN, contrast-enhanced 3D TOF MR angiography identified surgically verified neurovascular contact in 35 of 36 symptomatic nerves, and there was no false-positive. Based on surgical findings, the sensitivity of MR imaging was 97.2% and specificity 100%. The nature of the offending vessel was correctly identified in 94.4% of the patients by using the combination of contrast-enhanced and unenhanced MR angiography. Contrast-enhanced 3D TOF MR angiography is useful in the detection of vascular contact with the trigeminal nerve in patients with TN, and this MR imaging in combination with unenhanced MR angiography could help in the identification of the nature of the responsible vessels.

Diagnostic accuracy of contrast-enhanced MR angiography and unenhanced proton MR imaging compared with CT pulmonary angiography in chronic thromboembolic pulmonary hypertension

To evaluate the diagnostic accuracy of contrast-enhanced MR angiography (CE-MRA) and the added benefit of unenhanced proton MR angiography compared with CT pulmonary angiography (CTPA) in patients with chronic thromboembolic disease (CTE). A 2 year retrospective study of 53 patients with chronic thromboembolic pulmonary hypertension who underwent CTPA and MRI for suspected pulmonary hypertension and a control group of 36 patients with no CT evidence of pulmonary embolism. The MRI was evaluated for CTE and the combined diagnostic accuracy of ce-MRA and unenhanced proton MRA was determined. CE-MRA generated lung perfusion maps were also assessed. The overall sensitivity and specificity of CE-MRA in diagnosing proximal and distal CTE were 98% and 94%, respectively. The sensitivity improved from 50% to 88% for central vessel disease when CE-MRA images were analysed with unenhanced proton MRA. The CE-MRA identified more stenoses (29/18), post-stenosis dilatation (23/7) and occlusions (37/29) compared with CTPA. The CE-MRA perfusion images showed a sensitivity of 92% for diagnosing CTE. CE-MRA has high sensitivity and specificity for diagnosing CTE. The sensitivity of CE-MRA for visualisation of adherent central and lobar thrombus significantly improves with the addition of unenhanced proton MRA which delineates the vessel wall.

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Unenhanced calf MR angiography at 3.0 T using electrocardiography-gated partial-fourier fast spin echo imaging with variable flip angle

This study was to evaluate diagnostic performance of unenhanced electrocardiography-gated fast spin echo based MRA with variable flip angle on 3.0 T for assessment of calf arteries in patients with peripheral arterial occlusive disease (PAOD). 64 patients underwent unenhanced MRA (UE), time-resolved contrast-enhanced MRA of the calf and bolus-chase contrast-enhanced lower peripheral MRA (BCE). Diagnostic performance of UE was evaluated and compared with contrast-enhanced MRA in 61 patients and x-ray angiography in 10 patients. With UE, 852 of 960 segments (88.75%) were diagnostic even in patients with arrhythmia, demonstrating similar image quality with those on BCE (P > 0.05). For those diagnostic segments, statistics revealed good agreement between unenhanced and contrast-enhanced techniques with a Kappa value of 0.77 and 0.75 for stenosis detection and visualized vessel length, respectively. When using X-ray angiography as reference standard, no significant difference was found between UE and contrast-enhanced MRA concerning sensitivity and specificity in depiction of severe stenosis and occlusion (P > 0.05). Although further technical refinements are required, this optimized UE technique may be used as a supplement to contrast-enhanced MRA particularly in patients with PAOD in whom venous contamination occurs frequently.

High-Resolution 3D Unenhanced ECG-Gated Respiratory-Navigated MR Angiography of the Renal Arteries: Comparison With Contrast-Enhanced MR Angiography

The aim of this study is to determine the diagnostic value of high-resolution 3D unenhanced ECG-gated respiratory-navigated MR angiography (MRA) of the renal arteries using a steady-state free precession (SSFP) technique in comparison with 1.0-molar contrast-enhanced MRA in patients with suspected renal artery stenosis. Forty-five consecutive patients underwent unenhanced MRA before contrast-enhanced MRA within the same session. We assessed examination time, image quality, renal artery architecture, and localization and severity of renal artery stenosis. Examination time was shorter for contrast-enhanced MRA (mean ± SD, 12 ± 3 minutes) than for unenhanced MRA (19 ± 3 minutes; p < 0.001). On a 5-point scale, the image quality was similar for contrast-enhanced MRA (3.8 ± 1.0) and unenhanced MRA (4.0 ± 1.3; p = 0.24). Contrast-enhanced MRA offered more assessable data sets than did unenhanced MRA (95% vs 90%); however, unenhanced MRA had more data sets with maximum image quality (49% vs 30%). There was moderate agreement in stenosis grading between both MRA techniques (κ = 0.51; p < 0.001), but in only one case (1.3%) we found mismatch of more than one severity stenosis grade (stenoses > 75%). Sensitivity, specificity, and positive and negative predictive values of unenhanced MRA to detect renal artery stenoses greater than 50% were 75%, 99%, 75%, and 99%, respectively. We show that SSFP 3D unenhanced MRA is a very promising technique for patients with suspected renovascular disease and could be used as an alternative if gadolinium-based contrast agents cannot be administered.