Magnetic Resonance Angiography Sequence Research Articles

Non-contrast enhanced magnetic resonance angiography techniques in candidates for kidney transplantation: A comparative study

AimDetailed knowledge of vessel status in potential candidates for kidney transplantation is essential for the surgeon. Contrast enhanced magnetic resonance angiography has previously been used intensively for assessing this, but the discovery that use of gadolinium based contrast agents in magnetic resonance imaging can cause Nephrogenic Systemic Fibrosis in patients suffering from severe kidney disease has lead to renewed interest in non-contrast enhanced magnetic resonance angiography. The aim of this study was to find a non-contrast enhanced magnetic resonance angiography method for preoperative evaluation of the pelvic vessels prior to kidney transplantation, providing a sufficient image quality. MethodIn a prospective study we consecutively included 54 patients undergoing examinations prior to kidney transplantation. The patients were examined with the following magnetic resonance angiography sequences: A 2D Time of flight (n = 54), 3D Time of flight (n = 52) patients, 3D Phase Contrast (n = 54), 3D Balanced Steady State Free Precession (n = 52) and a 2D TRiggered Angiography Non-Contrast Enhanced (TRANCE) (a Spin Echo sequence with subtraction) (n = 48). The sequences were evaluated with respect to contrast, diagnostic performance and artefact burden. ResultsEvaluating contrast, 3D Phase Contrast was significantly better than 2D Time of flight (p < 0.001). The 2D Time of flight was significantly superior to 3D Time of flight, 3D Balanced-Turbo Steady State Free Precession and the TRANCE sequences (p < 0.001). Rating diagnostic performance, the 3D Phase Contrast ranked better than the 2D Time of flight though no significant difference was found (p > 0.2). The 2D Time of flight was significantly better than the other sequences (p < 0.001) in all cases. The artefact score was lowest for the Phase Contrast images and significantly superior to the 2D Time of flight (p < 0.005). The 2D Time of flight was significantly better than the three other sequences (p < 0.001) in all cases. ConclusionNon-contrast enhanced magnetic resonance angiography offers a safe preoperative examination for assessment of vessel status before kidney transplantation. A combination of 2D Time of flight and 3D Phase Contrast acquisitions is recommended and can be performed within a reasonable scan time.

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.

Technical innovation in dynamic contrast-enhanced magnetic resonance imaging of musculoskeletal tumors: an MR angiographic sequence using a sparse k-space sampling strategy

We demonstrate the clinical use of an MR angiography sequence performed with sparse k-space sampling (MRA), as a method for dynamic contrast-enhanced (DCE)-MRI, and apply it to the assessment of sarcomas for treatment response. Three subjects with sarcomas (2 with osteosarcoma, 1 with high-grade soft tissue sarcomas) underwent MRI after neoadjuvant therapy/prior to surgery, with conventional MRI (T1-weighted, fluid-sensitive, static post-contrast T1-weighted sequences) and DCE-MRI (MRA, time resolution = 7-10 s, TR/TE 2.4/0.9 ms, FOV 40 cm(2)). Images were reviewed by two observers in consensus who recorded image quality (1 = diagnostic, no significant artifacts, 2 = diagnostic, <25 % artifacts, 3 = nondiagnostic) and contrast enhancement characteristics by static MRI (presence/absence of contrast enhancement, percentage of enhancement) and DCE-MRI (presence/absence of arterial enhancement with time-intensity curves). Results were compared with histological response (defined as <5 % viable tumor [soft tissue sarcoma] or <10 % [bone sarcoma] following resection). Diagnostic quality for all conventional and DCE-MRI sequences was rated as 1. In 2 of the 3 sarcomas, there was good histological response (≤5 % viable tumor); in 1 there was poor response (50 % viable tumor). By static post-contrast T1-weighted sequences, there was enhancement in all sarcomas, regardless of response (up to >75 % with good response, >75 % with poor response). DCE-MRI findings were concordant with histological response (arterial enhancement with poor response, no arterial enhancement with good response). Unlike conventional DCE-MRI sequences, an MRA sequence with sparse k-space sampling is easily integrated into a routine musculoskeletal tumor MRI protocol, with high diagnostic quality. In this preliminary work, tumor enhancement characteristics by DCE-MRI were used to assess treatment response.

Diagnostic Performance of a Non–Contrast-Enhanced Magnetic Resonance Imaging Protocol for Potential Living Related Kidney Donors

The objective of the study was to evaluate the performance of a non-contrast-enhanced magnetic resonance (MR) imaging protocol for preoperative screening of living related kidney donors. Forty consecutive subjects (mean age 52.2 ± 11.3 years, range 29-73 years) underwent MR imaging with T2-weighted sequences (coronal and axial plane), with a non-contrast-enhanced respiratory-gated three-dimensional steady state free precession MR angiography (NCE-MRA) sequence and with contrast-enhanced magnetic resonance MR angiography (CE-MRA) sequences in the arterial and venous phases. Two blinded readers independently assessed arterial and venous anatomy and potential kidney lesions. Results of non-contrast-enhanced images were compared to CE-MRA and in a subgroup of 21 subjects to surgery as standard of reference. Regarding arterial anatomy, NCE-MRA yielded sensitivity, specificity, and accuracy of 100%, 89%, and 91% compared to CE-MRA. Three kidneys were found to have more accessory renal arteries at NCE-MRA than at CE-MRA. In the subgroup of 21 subjects, 1 surgically proven accessory artery was depicted with NCE-MRA but not with CE-MRA. Accuracy of T2-weighted images regarding accessory veins or variant venous course was 99%, with one missed circumaortic vein on T2-weighted images. Two simple cysts were missed on T2-weighted and NCE-MRA but not on CE-MRA images. A non-contrast-enhanced MR imaging protocol including NCE-MRA and T2-weighted images allows for the accurate screening of living related kidney donors and may serve as an alternative to CE-MRA.

Direct coronary motion extraction from a 2D fat image navigator for prospectively gated coronary MR angiography

Direct 2D tracking of cardiac motion may provide superior respiratory navigator gating for coronary magnetic resonance angiography compared to conventional liver-diaphragm navigators. However, additional 2D processing for motion extraction is unsuitable for real-time prospective gating. In this work, a 2D fat-selective image navigator, which delineates the epicardial fat surrounding coronary arteries, is developed to directly monitor epicardial fat motion at every heartbeat in real-time for prospective gating. The proposed navigator is incorporated into a real-time interactive software that allows rapid setup and efficient motion extraction, and runs on standard clinical hardware without any additional dedicated components for processing. The proposed 2D cardiac fat image navigator was compared with the conventional 1D diaphragm navigator in free-breathing b-SSFP coronary MRAs in 12 healthy volunteers at 1.5T. Real-time motion extraction from 2D cardiac fat navigator images was feasible within 20 ms, enabling successful prospectively gated coronary magnetic resonance angiographies in all subjects. Compared to 1D diaphragmatic navigator, 2D fat image navigator reduced scan time by 38% (P < 0.0005), and significantly improved vessel sharpness, myocardial suppression, and image quality (P < 0.05). This demonstrates the feasibility of a 3D SSFP coronary magnetic resonance angiography sequence using a 2D epicardial fat image as a navigator for real-time prospective motion tracking.

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.

Brain mechanical property measurement using MRE with intrinsic activation

Many pathologies alter the mechanical properties of tissue. Magnetic resonance elastography (MRE) has been developed to noninvasively characterize these quantities in vivo. Typically, small vibrations are induced in the tissue of interest with an external mechanical actuator. The resulting displacements are measured with phase contrast sequences and are then used to estimate the underlying mechanical property distribution. Several MRE studies have quantified brain tissue properties. However, the cranium and meninges, especially the dura, are very effective at damping externally applied vibrations from penetrating deeply into the brain. Here, we report a method, termed ‘intrinsic activation’, that eliminates the requirement for external vibrations by measuring the motion generated by natural blood vessel pulsation. A retrospectively gated phase contrast MR angiography sequence was used to record the tissue velocity at eight phases of the cardiac cycle. The velocities were numerically integrated via the Fourier transform to produce the harmonic displacements at each position within the brain. The displacements were then reconstructed into images of the shear modulus based on both linear elastic and poroelastic models. The mechanical properties produced fall within the range of brain tissue estimates reported in the literature and, equally important, the technique yielded highly reproducible results. The mean shear modulus was 8.1 kPa for linear elastic reconstructions and 2.4 kPa for poroelastic reconstructions where fluid pressure carries a portion of the stress. Gross structures of the brain were visualized, particularly in the poroelastic reconstructions. Intra-subject variability was significantly less than the inter-subject variability in a study of six asymptomatic individuals. Further, larger changes in mechanical properties were observed in individuals when examined over time than when the MRE procedures were repeated on the same day. Cardiac pulsation, termed intrinsic activation, produces sufficient motion to allow mechanical properties to be recovered. The poroelastic model is more consistent with the measured data from brain at low frequencies than the linear elastic model. Intrinsic activation allows MRE to be performed without a device shaking the head so the patient notices no differences between it and the other sequences in an MR examination.

Time‐of‐flight magnetic resonance angiography (TOF‐MRA) of the normal equine head

Noncontrast magnetic resonance angiography (MRA) is widely used in human and small animal medicine. However, this technique has not yet been described in the horse, and compared to other angiographic techniques MRA could be more cost efficient and potentially safer. The aim of this study was to provide a comprehensive anatomical reference of the normal equine head vasculature using a noncontrast MRA technique, on both low- and high-field MRI. Five healthy adult horses were examined, 4 with a low-field magnet (0.23T) and the remaining one with a high-field magnet (1.5T). The magnetic resonance angiography sequence used was TOF (time-of-flight) 2D-MRA and CT images of a vascular corrosion cast were subsequently used as anatomical references. The MRA imaging protocol provided good visualisation of all major intra- and extracranial vessels down to a size of approximately 2 mm in diameter on both low- and high-field systems. This resulted in identification of vessels to the order of 3rd-4th branches of ramification. The visibility of the arteries was higher than of the veins, which showed lower signal intensity. Overall, MRA obtained with the high-field protocol provided better visualisation of the arteries, showing all the small arterial branches with a superior resolution. The use of a specific vascular sequence such as TOF 2D-MRA allows good visualisation of the equine head vasculature and eliminates the need for contrast media for MRA. Magnetic resonance angiography allows for visualisation of the vasculature of the equine head. Vessel morphology, symmetry and size can be evaluated and this may possibly play a role in preoperative planning or characterisation of diseases of the head, such as neoplasia or guttural pouch mycosis.

Basi-parallel Anatomical Scanning (BPAS)-MRI Can Improve Discrimination of Vertebral Artery Dissection from Atherosclerosis and Hypoplasia

The purpose of this study was to determine the effectiveness of combining basi-parallel anatomic scanning (BPAS)-magnetic resonance (MR) imaging findings with those of time-of-flight (TOF)-MR angiography (MRA) for differentiating vertebral artery dissection (VAD) from other causes of true artery narrowing such as atherosclerosis or an anatomical variation such as vertebral artery hypoplasia. Fifteen cases of VAD, 15 of atherosclerotic narrowing, and 8 of hypoplastic vertebral arteries were retrospectively selected for this study. Conventional MR sequences (T1WI, T2WI, and T2*WI, fluid attenuation inversion recovery, TOF-MRA) and BPAS images were analyzed by two readers blinded to the patients' clinical data and history. Receiver operating characteristic analyses were performed to compare the diagnostic capability of conventional MR sequences with and without BPAS imaging in suspected VAD cases. The area under the curve increased significantly by combining BPAS imaging findings with those of conventional MRI (0.72 vs. 0.96 and 0.81 vs. 0.99; P = .0022 and P = .0068, respectively, for readers 1 and 2). In addition, the sensitivity was 100% (15/15) for both readers and significantly greater than that of conventional MRI (53.3% [8/15] for both readers, P = .0156); however, specificities were not significantly different (82.6% [19/23] vs. 82.6% [19/23] and 91.33% [21/23] vs. 95.7% [22/23]). The interobserver agreement also improved by adding BPAS imaging. Adding BPAS imaging to conventional MRI and MRA sequences can improve diagnostic capability and sensitivity in suspected VAD cases and be helpful in differentiating it from other causes of vertebral artery narrowing such as atherosclerosis or hypoplasia.

In vitro stent lumen visualisation of various common and newly developed femoral artery stents using MR angiography at 1.5 and 3 tesla

To evaluate stent lumen assessment of various commonly used and newly developed stents for the superficial femoral artery (SFA) using MR angiography (MRA) at 1.5 and 3 T. Eleven nitinol stents and one cobalt-chromium stent were compared regarding stent lumen visualisation using a common three-dimensional MRA sequence. Maximum visible stent lumen width and contrast ratio were analysed in three representative slices for each stent type. A scoring system for lumen visualisation was applied. Nitinol stents showed significantly better performance than the cobalt chromium stent (P < 0.05) at 1.5 and 3 T. Maximum visible stent lumen ranged between 43.4 and 95.5 %, contrast ratio between 7.2 and 110.6 %. Regarding both field strengths, seven of the nitinol stents were classified as "suitable". Three nitinol stents were "limited", and one nitinol stent and the cobalt chromium stent were "not suitable". Intraluminal loss of signal and artefacts of most of the SFA stents do not markedly limit assessment of stent lumen by MRA at 1.5 and 3 T. MRA can thus be considered a valid technique for detection of relevant in-stent restenosis. Applied field strength does not strongly influence stent lumen assessment in general, but proper choice of field strength might be helpful.

Triple-TWIST MRA: high spatial and temporal resolution MR angiography of the entire peripheral vascular system using a time-resolved 4D MRA technique

Multi-station contrast-enhanced magnetic resonance angiography (MRA) is considered as the imaging investigation of first choice in patients suffering from peripheral arterial occlusive disease. In order to overcome venous overlay and to gain dynamic flow information as provided by digital subtraction angiography (DSA), we developed a triple injection protocol for high-resolution MRA of the entire peripheral vascular system, applying time-resolved (TR) four-dimensional (4D) MRA sequences. Ten patients underwent three-station TR-MRA of the pelvis and lower extremities with DSA as reference standard. Both investigations were compared concerning stenosis on a segment-by-segment basis. Furthermore, 28 consecutive patients underwent the same MR-only imaging protocol. All images were evaluated concerning image quality (1 = non-diagnostic, 4 = excellent), venous overlay (from none up to substantial) and time to venous enhancement (very early/early/normal/late). Three-station TR-MRA proved feasible and was comparable with DSA in 282 vessel segments, with underestimation grade of stenosis in four segments and overestimation in four segments, respectively. In 32/38 patients no venous overlay was noted; in six patients there was mild venous overlay. Image quality was rated excellent or good in most cases. TR-MRA provides morphological and functional information without any timing issues due to optimal arterial enhancement at high spatial resolution without venous overlay.

Follow-up of coiled intracranial aneurysms: comparison of 3D time-of-flight and contrast-enhanced magnetic resonance angiography at 3T in a large, prospective series

To compare 3D-TOF magnetic resonance angiography (MRA) and contrast-enhanced MRA (CE-MRA) sequences at 3T in the follow-up of coiled aneurysms with digital subtracted angiography (DSA) as the gold standard. DSA, 3D-TOF and CE-MRA were performed in a prospective series of 126 aneurysms in 96 patients (57 female, 39 male; age: 25-75years, mean: 51.3 ± 11.3years). The quality of aneurysm occlusion was assessed independently and anonymously by a core laboratory. Using DSA (gold standard technique), total occlusion was depicted in 57 aneurysms (45.2%), neck remnant in 34 aneurysms (27.0%) and aneurysm remnant in 35 aneurysms (27.8%). Sensitivity, specificity, positive predictive value and negative predictive value were very similar with 3D-TOF and CE-MRA. Visibility of coils was much better with 3D-TOF (95.2%) than with CE-MRA (23.0%) (P < 0.001). Also, substantial artefacts were less frequent with 3D-TOF (4.0%) than with CE-MRA (11.9%; P = 0.012). In this large prospective series of patients with coiled aneurysms, at 3T 3D-TOF MRA was equivalent to CE-MRA for the evaluation of aneurysm occlusion, but coil visibility was superior at 3D-TOF. Thus the use of 3D-TOF at 3T is recommended for the follow-up of coiled intracranial aneurysms. • Different Magnetic Resonance (MR) imaging techniques are used to evaluate intracranial aneurysms. • At 3T MR, 3D-TOF and CE-MRA appear equivalent for evaluating coiled aneurysms.. • Coils are better visualised on 3D-TOF than on CE-MRA. • Combined analysis of 3D-TOF and CE-MRA does not seem helpful. • At 3T, 3D-TOF techniques are recommended for monitoring patients with coiled aneurysms.

Magnetic resonance imaging for diagnosis of acute pulmonary embolism: not yet a suitable alternative to CT‐PA

See also Revel MP, Sanchez O, Couchon S, Planquette B, Hernigou A, Niarra R, Meyer G, Chatellier G. Diagnostic accuracy of magnetic resonance imaging for acute pulmonary embolism: results of the ‘IRM-EP’ study. This issue, pp 743–50; and Sodhi KS, Saxena AK. Diagnostic accuracy of computed tomography pulmonary angiography and magnetic resonance imaging for an acute pulmonary embolism. This issue, pp 961.

Magnetic resonance imaging/magnetic resonance angiography fusion technique for intraoperative navigation during microsurgical resection of cerebral arteriovenous malformations

Microsurgical resection of arteriovenous malformations (AVMs) is facilitated by real-time image guidance that demonstrates the precise size and location of the AVM nidus. Magnetic resonance images have routinely been used for intraoperative navigation, but there is no single MRI sequence that can provide all the details needed for characterization of the AVM. Additional information detailing the specific location of the feeding arteries and draining veins would be valuable during surgery, and this detail may be provided by fusing MR images and MR angiography (MRA) sequences. The current study describes the use of a technique that fuses contrast-enhanced MR images and 3D time-of-flight MR angiograms for intraoperative navigation in AVM resection. All patients undergoing microsurgical resection of AVMs at the Dartmouth Cerebrovascular Surgery Program were evaluated from the surgical database. Between 2009 and 2011, 15 patients underwent surgery in which this contrast-enhanced MRI and MRA fusion technique was used, and these patient form the population of the present study. Image fusion was successful in all 15 cases. The additional data manipulation required to fuse the image sets was performed on the morning of surgery with minimal added setup time. The navigation system accurately identified feeding arteries and draining veins during resection in all cases. There was minimal imaging-related artifact produced by embolic materials in AVMs that had been preoperatively embolized. Complete AVM obliteration was demonstrated on intraoperative angiography in all cases. Precise anatomical localization, as well as the ability to differentiate between arteries and veins during AVM microsurgery, is feasible with the aforementioned MRI/MRA fusion technique. The technique provides important information that is beneficial to preoperative planning, intraoperative navigation, and successful AVM resection.

Susceptibility-Weighted Imaging: A New Tool in the Diagnosis and Evaluation of Abnormalities of the Vein of Galen in Children

We retrospectively identified 9 consecutive children, 3 males and 6 females (age 5.2 ± 6.3 years, range 1 day to 18 years), with known or suspected AVGs who underwent MR imaging, including SWI, at our institution between January 2007 and March 2011. On the SWI sequence, arterialized blood flow was considered to be present in the vein of Galen or its tributaries when these showed abnormal signal hyperintensity from arteriovenous shunting. SWI findings were correlated with findings from DSA studies or findings from time-of-flight or contrast-enhanced MR angiography sequences. SWI was found to accurately differentiate between high-flow and low-flow AVGs and was also useful in characterizing the arterial supply and venous drainage patterns associated with high-flow AVGs.

Abstract 167: High Resolution MR Imaging Of Intracranial Arterial Vessel Walls In Moyamoya Disease

Background: The pathogenesis of the primary occlusive vasculopathy or vasculopathies involving the basal arteries in patients with moyamoya phenomenon is unknown. Newer Magnetic Resonance (MR) techniques have been developed to characterize atheroma in the arterial wall. This is a pilot study of vessel wall imaging using high field-strength, high-spatial resolution MR techniques in patients with moyamoya. Method: Twenty patients with idiopathic moyamoya were recruited. MR imaging was performed on a 3T head MR system. Imaging included a time-of-flight (TOF) magnetic resonance angiography (MRA) and high-resolution T2-weighted sequences through the circle of Willis. Images were inspected for evidence of an intramural occlusive lesion or atheroma. Vessel wall thickness of the internal carotid artery (ICA) at the points of maximal narrowing as determined by catheter angiography was compared to the wall thickness of the distal basilar artery in each patient. Vessel wall thickness was calculated as the difference between the intraluminal diameter measured on MRA and the extraluminal diameter measured on the T2 image, divided by 2. Results: All patients demonstrated diminished arterial diameters on T2 imaging corresponding to sites of luminal stenosis on catheter angiography and time-of-flight MRA sequences. No focal or diffuse intramural thickening was subjectively observed at the sites of stenosis. Objective measures of vessel wall thickness found no difference between the sites of maximal stenosis of involvded vessels and univolved vessels of similar diameter. The mean thickness of the basilar artery was 0.66 mm (standard deviation 0.14). The mean thickness of the diseased ICA was 0.61 mm (s.d. 0.22) in patients with bilateral disease. The mean thickness of the uninvolved ICA in patients with unilateral disease was 0.69 mm (s.d. 0.07). The figure includes sequential high resolution T2 images of a patients with unilateral right sided moyamoya phenomenon (a,b) demonstrating a small right ICA (arrow) compared to the unaffected contralateral ICA. TOF MRA (c,d) illustrate luminal stenosis without evidence of intramural thickening. Multiple moyamoya collateral vessels are also evident (c). Conclusion: These data suggest that the pathological process underlying vessel narrowing and occlusion is not a static structural lesion in the vessel wall leading to luminal compromise. In addition, these imaging techniques may be useful in distinguishing idiopathic basal occlusive disease from other processes such as atherosclosis.

Non-contrast-enhanced magnetic resonance angiography: techniques and applications

Non-contrast-enhanced magnetic resonance angiography has gained renewed interest since the discovery of the association between gadolinium-based contrast agents and nephrogenic systemic fibrosis. The following article is an overview of the different magnetic resonance angiography sequences, the technical possibilities and new developments. Clinical options and recent advancements will be highlighted, and recommendations for non-contrast-enhanced magnetic resonance angiography techniques in different anatomical regions will be given. Furthermore, the authors seek to predict the future of non-contrast-enhanced magnetic resonance angiography, with special focus on patients at risk.

Contrast-Enhanced Magnetic Resonance Angiography in Rabbits

: To evaluate the performance of a gadolinium-based contrast compound (P846) as well as an ultra-small particle of iron oxide agent (P904) in contrast-enhanced magnetic resonance angiography (MRA) in rabbits and to compare those agents with gadoterate meglumine (Gd-DOTA) for first pass and steady state imaging. : A total of 6 rabbits underwent contrast-enhanced MRA of the aorta and its branches at 3 different time points. All examinations were performed on a 1.5T MR (Siemens HealthCare, Magnetom Espree), and the contrast agents were applied in random order. Image data were acquired using a time-resolved MRA sequence (time-resolved angiography with stochastic trajectories) during the first pass to assess the bolus phase and a high-resolution MRA sequence followed by repetitive measurements over the next 10 minutes for all 3 agents to evaluate the postbolus phase. Two radiologists reviewed the images in consensus blinded to the contrast agent used. Signal-to-noise ratio and contrast-to-noise ratio for three-dimensional high-resolution MRA were calculated for each time point and agent. Image quality was consensually evaluated on a 4-point Likert scale. A Wilcoxon-Mann-Whitney U test was used for comparison with P < 0.05 as level of statistical significance. : All agents led to diagnostic MR angiograms in all 6 rabbits. The time-resolved angiography with stochastic trajectories datasets provided detailed information about the bolus phase for all the 3 agents. During the first pass, P904 and P846 proved to be superior to Gd-DOTA with the highest peak enhancement for P846. In the postbolus phase up to 10 minutes postcontrast injection, P904 proved to be superior to the other agents. All the agents led to excellent image quality, with no statistical difference to a maximum of 3 minutes postinjection, whereas thereafter images with Gd-DOTA and P846 were assessed as nondiagnostic. : P846 and P904 proved to be superior to Gd-DOTA for time-resolved MRA. The ultra-small particle of iron oxide compound P904 showed continuous high signal over 10 minutes and seems to be best suited for first pass and steady-state imaging.

Assessment of qualitative and quantitative features in coronary artery MRA

In this paper, an analysis of the coronary trees using magnetic resonance angiography (MRA) is performed. The objective is to estimate how much MRA is capable to provide insights into the vascular network. A qualitative exploration of the MRA volumes with anatomical labelling by experts is first performed, Quantitative vessel features are then manually extracted providing a ground truth which is further compared to a semi-automatic extraction. This evaluation is carried out on 10 datasets of the SSFP MRA sequence and allows getting a more precise view on the current state-of-the- art as well as on future achievements to be done.

Simultaneous Visualization of Nerves and Vessels of the Lower Extremities Using Magnetization-Prepared Susceptibility Weighted Magnetic Resonance Imaging at 3.0 T

Identifying the extent of involvement of the vessel and nerve, particularly in regard to preoperative evaluation and precise localization of the tumor and its relation to the structures of the extremities, has important applications for advancing the treatment of lower extremity diseases. To review the technical feasibility of simultaneous visualization of nerves and vessels of the lower extremities by using magnetization-prepared susceptibility-weighted magnetic resonance (MR) imaging (MP-SWI) at 3.0T. Ten healthy volunteers and 10 patients were studied. Optimized MP-SWI, MR neurography (MRN) based on 3D diffusion-weighted steady-state free precession imaging and contrast-enhanced MR angiography (CE-MRA) sequences were performed for each subject. The means of signal-to-noise ratio (SNR)n, SNRv, SNRm, contrast-to-noise ratio (CNR)n,m and CNRv,m were calculated and the certainty of identifying nerves and vessels was determined. CNRn,m between MP-SWI and MRN, and CNRv,m between MP-SWI and CE-MRA were compared. MP-SWI provides slightly poorer CNRv,m than CE-MRA, whereas MP-SWI provides a better CNRn,m than MRN. In thin-slice-thickness maximum-intensity projection arbitrary planes, the sciatic nerve and its branches were clearly identified (score 1 or 2 of 2) in 17 subjects (85%); the femoral artery and the main branches were identified (score 1 or 2 of 2) in all 20 subjects (100%). The nerves are isointense to slightly hypointense to muscle, and the vessels show a more obvious hyperintense signal than muscle in MP-SWI. The proposed MP-SWI demonstrates the feasibility of simultaneously visualizing nerves and vessels of the lower extremities without using an exogenous contrast agent. It may enable straightforward localization of a disease process to a specific nerve and vessel.