Aortoiliac stenooculusive disease and aneurysms: screening with non-contrast enhanced two-dimensional cardiac gated cine phase contrast MR angiography with multiple velocity encoded values and cardiac gated two-dimensional time-of-flight MR angiography

PURPOSE: To evaluate the performance of two-dimensional cine phase contrast MRA with multi-velocity encoded values (multi-VENC cine PC) and ECG-gated two-dimensional time-of-flight MRA (ECG-2D-TOF) for the detection of stenoocclusive lesions and aneurysms in the aortoiliac area, when each method was used individually and when the two methods were used together. METHODS: Forty-one patients were included in this study. Multi-VENC cine PC and ECG-2D-TOF were obtained first, then contrast enhanced three-dimensional magnetic resonance angiography (CE-3D-MRA) was performed as the standard of reference. Two observers reviewed the images separately without knowledge of patients' symptoms or histories. Sensitivities and specificities were obtained separately for stenooclusive lesions and aneurysms by two reviewers. RESULTS: When the two methods were applied together, high sensitivities (93.0 by observer 1 and 91.9% by observer 2) and adequate specificities (87.6 and 82.3%) were obtained for stenoocclusive lesions. For aneurysms, moderate to high sensitivities (91.1 and 71.1%) and high specificities (98.8 and 99.4%) were obtained. CONCLUSION: These results suggest that the performance of two non-contrast enhanced MRA techniques may be valuable as a screening tool when the two methods are applied together.     

Evaluation of subclavian steal with two-dimensional phase-contrast and two-dimensional time-of-flight MR angiography.

We describe two MR angiographic methods of diagnosing subclavian steal in each of three patients. By using phase-directional information from a single two-dimensional phase-contrast sequence, we were able to show that the direction of flow in the affected vertebral artery was reversed. The same vertebral artery showed no signal on a 2-D time-of-flight sequence with a concatenated presaturation pulse applied above each section.     

Carotid artery stenosis: clinical efficacy of two-dimensional time-of-flight MR angiography.

To assess the clinical efficacy of two-dimensional time-of-flight magnetic resonance (MR) angiography in the evaluation of carotid artery stenosis, a group of patients was evaluated in which 73 vessels were studied with both MR and conventional angiography. Four experienced neuroradiologists each scored both the MR and conventional angiograms in a blinded manner by using a standardized scoring scheme. Comparison of the scores revealed a high degree of correlation. In particular, MR angiography served to discriminate reliably between mildly narrowed and severely narrowed or occluded vessels. Furthermore, severe stenoses were accurately discriminated from occlusions in all cases. MR angiography is a robust and accurate modality for the characterization of carotid artery stenosis. It is useful in conjunction with routine MR imaging of the brain in the evaluation of the patient with suspected carotid arterial disease.     

Pulsatile flow artifacts in two-dimensional time-of-flight MR angiography: Initial studies in elastic models of human carotid arteries

Initial experimental and numerical analysis of artifacts due to pulsatile flow in two-dimensional time-of-flight (2D-TOF) magnetic resonance (MR) angiography are presented. The experimental studies used elastic models of the carotid artery bifurcation cast from fresh cadavers and accurately reproducing the twisting and tapering of the human blood vessels, allowing direct comparison of images with and without flow. Prominent image artifacts, including periodic ghosts and signal loss, were produced by pulsatile flow even though flow-compensated gradient waveforms were used. The dependence of artifacts due to partial saturation on pulse sequence parameters (TR and flip angle) was investigated theoretically for a simple pulsatile velocity profile and compared with experimental results from a model of a normal carotid artery. Signal reduction was observed proximal and distal to the stenosis in a model with a 70% internal carotid artery (ICA) stenosis and a model with 90% stenoses in both the ICA and the external carotid artery. Although this study deals exclusively with 2D-TOF imaging, the methods can also be applied to evaluate other MR angiography techniques.     

Three-dimensional magnetization-prepared time-of-flight MR angiography of the carotid and vertebral arteries

Three-dimensional magnetization-prepared (MP) MR angiography (MRA) was applied to the carotid and vertebral arteries by using ECG triggering, a slab selective RF inversion pulse, centric phase encoding and acquisition during diastole. Both theoretically and experimentally, the MP MRA sequence was shown to perform well in cases where there was substantial blood replenishment during the inversion time Tl (>330 ms). In comparison with standard, ungated, steady-state 3D time-of-flight MRA in 13 consecutive volunteers, the MP MRA images demonstrated better background suppression with less artifact and generally had more uniform vessel depiction. The MP MRA sequence was generally superior for portraying vessels exhibiting high pulsatility such as the carotid siphon. However, in distal vessels with slow flow and incomplete blood replenishment, the MP MRA technique was inferior due to increased loss of vessel signal. The reasons for this increased signal loss are identified and improvements to the MP MRA sequence are suggested.     

Multiple breathhold 3D time-of-flight MR angiography of the renal arteries

A technique is described for angiographic imaging of the renal arteries with acquisition performed over several periods of suspended respiration. The 3D Fourier transform (FT) gradient-echo angiographic sequence uses magnetization preparation and appropriately chosen delay times for background nulling and time-of-flight enhancement of the vasculature. The sequence was applied to 10 volunteers, each of whom was imaged in three ways: (i) over a series of breathholds in which feedback was provided to enable reproducible breath-holding; (ii) over a series of breathholds with no feedback; and (iii) over continuous respiration. Results were evaluated by measuring the transverse extent of the well-delineated renal vasculature and by noting the distal extent of the vasculature branching (main, segmental, and interlobar branches). The transverse extent of renal vasculature visible with breathhold feedback, breathholding, and free breathing was 6.1 ± 0.9 cm, 5.0 ±1.8 cm, and 4.0 ±1.4 cm, respectively (mean ± SD). Breathhold feedback enabled visualization of segmental renal arteries bilaterally in all 10 volunteers.     

High-resolution multiphase contrast-enhanced three-dimensional MR angiography compared with two-dimensional time-of-flight MR angiography for the identification of pedal vessels

PURPOSE: The authors prospectively evaluated optimized multiphase high-resolution (HR) Gadolinium (Gd)-enhanced three-dimensional (3D) magnetic resonance (MR) angiography and standard two-dimensional (2D) time-of-flight (TOF) MR angiography for their ability to delineate distal calf and pedal vessels. MATERIALS AND METHODS: Twelve patients (20 limbs) with limb-threatening peripheral arterial occlusive disease underwent HR Gd-enhanced and 2D TOF MR angiography to identify targets for distal bypass. Imaging of the region of the ankle and foot was performed on a 1.5 T system with a head coil. A standard 2D TOF MR angiography sequence was performed first. The HR Gd-enhanced MR angiography sequence was then performed after injection of 0.01-0.2 mmol/kg of gadodiamide, allowing the acquisition of multiple consecutive coronal partitions, each in 18-25 seconds. Two experienced angiographers independently analyzed both studies. Comparison with intraoperative conventional angiography was available in 10 limbs. RESULTS: HR Gd-enhanced MR angiography allowed significantly faster imaging time (P <.0001) and larger coverage area (P <.0001) than 2D TOF MR angiography. All segments seen on 2D TOF MR angiography were visualized on HR Gd MR angiography, and significantly more suitable targets were seen well on HR Gd-enhanced MR angiography than on 2D TOF MR angiography (mean targets per limb: 3.9 +/- 1.9 vs 2.6 +/- 1.5, respectively; P =.02). In addition, HR Gd-enhanced MR angiography allowed better visualization of the arcuate pedal branch than 2D TOF MR angiography (P <.0001). Excellent correlation was demonstrated between HR Gd-enhanced MR angiography and intraoperative angiography in 29 segments (binary similarity coefficient, 0.90). A significantly higher percentage of artifacts adversely affected image interpretation with 2D TOF MR angiography than with HR Gd-enhanced MR angiography (14 limbs vs five limbs, P <.001). Artifacts on HR Gd-enhanced MR angiography included suboptimal mask in two limbs, venous contamination in one patient (two limbs), and motion artifact in one limb, although the studies remained diagnostic in all cases. CONCLUSION: HR Gd-enhanced MR angiography identified more distal target vessels with greater confidence than 2D TOF MR angiography. Optimized HR Gd-enhanced MR angiography may replace 2D TOF MR angiography as the gold standard examination for evaluation of distal runoff.     

MRI of thoracic vascular lesions with emphasis on two-dimensional time-of-flight MR angiography

MRI is a valuable method for evaluating thoracic vascular lesions by virtue of its non-invasiveness and multiplanar capability. In addition, ionizing radiation and iodinated contrast medium are not required. Electrocardiographically gated T1 weighted spin echo MRI remains the principal technique for demonstrating the anatomy and morphology of thoracic vascular diseases. Cine MRI allows dynamic evaluation of vascular flow, whereas MR angiography is particularly useful in the two-dimensional (2D) or three-dimensional (3D) display of vascular anatomy. This pictorial review illustrates the use of 2D time-of-flight MR angiography in the assessment of various thoracic vascular conditions including aortic arch and great vessel anomalies, heterotaxic syndromes, aortic dissection, aortic or arch vessel aneurysms, pulmonary embolism, pulmonary sequestration, axillofemoral bypass and tumour/vessel relationships.     

Moyamoya disease: diagnosis with three-dimensional time-of-flight MR angiography.

Twelve patients with moyamoya disease were studied with three-dimensional time-of-flight magnetic resonance (MR) angiography, and the findings were compared with results obtained with conventional arteriography. Of a total of 24 supraclinoid internal carotid arteries studied, 21 arteries (88%) were accurately evaluated with MR angiography and in three arteries the extent of occlusive disease was overestimated. Of a total of 72 large branch basal cerebral vessels, including the bilateral anterior, middle, and posterior cerebral arteries, 61 arteries (85%) were accurately evaluated with MR angiography and in 11 arteries the extent of occlusive disease was overestimated. While conventional arteriography showed basal cerebral moyamoya vessels in all 24 hemispheres, MR angiography showed moyamoya vessels in 20 of these. Of a total of 28 large leptomeningeal and transdural collateral vessels, 18 were identified with MR angiography. In the one surgical collateral vessel evaluated, MR angiography successfully showed its patency. MR angiography may have value in following disease progression and, perhaps, in evaluation of surgical bypass patency.     

Coronary arteries: breath-hold MR angiography

The authors describe a method for performance of ultrafast magnetic resonance (MR) angiography of coronary arteries with a standard clinical MR system and a body coil. Each image was obtained within a single breath hold by using an electrocardiography-gated, segmented, ultrafast, gradient-echo pulse sequence with an incremental excitation flip angle for the eight phase-encoding steps acquired per segment. By using overlapping 4-mm-thick sections, the coronary arteries were routinely depicted from the coronary ostia distally at MR in healthy subjects. Ultrafast MR angiography of the coronary arteries is feasible with use of a standard body coil. This technique offers considerable potential as an investigational tool and, with further development, may become a clinically useful imaging application.     

Carotid arteries: evaluation with low-field-strength MR angiography.

Magnetic resonance (MR) angiography of neck vessels was performed with a 0.2-T permanent magnet by using a two-dimensional, time-of-flight technique. Thirty-one patients were included in the study. The imaging parameters used included a repetition time of 60 msec, an echo time of 10 msec, a 90 degrees flip angle, and a 192 x 256 matrix; 40-50 sequential two-dimensional sections were acquired through the neck. Stenosis was graded on a scale of 1-5. Correlation of digital and MR angiography was made in the clinically nonrelevant cases (stenoses of grades 1 and 2), with overestimation to grade 3 in six cases. Two grade 3 stenoses were overestimated as grade 4. Severe stenoses were correctly characterized in all but one case, which was underestimated because of a segmental short extension of the stenotic lesion. Obstructions were found in two cases. Areas with a lack of signal were observed in four patients with severe stenosis and in two with tortuous arteries. Correct diagnosis, however, was achieved with analysis of the maximum intensity projection animation display. Low-field-strength MR angiography has the same clinical value as that performed with high field strengths.     

Real-time projection MR angiography: feasibility study

Intraarterial injections of small doses of gadopentetate dimeglumine were combined with a fast spoiled-gradient-echo magnetic resonance (MR) sequence to obtain real-time projection angiographic images of the rabbit aorta and canine coronary arteries. Arterial filling and washout, as well as venous and perfusion phases, were clearly displayed, demonstrating that arterial fluoroscopy in which an MR technique is used is feasible.     

Renal arteries: comparison of steady-state free precession MR angiography and contrast-enhanced MR angiography

All participants provided informed consent to participate in this study, which was approved by the institutional review board. Breath-hold three-dimensional (3D) steady-state free precession (SSFP) magnetic resonance (MR) angiography was compared with 3D contrast material-enhanced MR angiography in patients suspected of having renal artery stenosis. Two radiologists assessed visualization of renal arteries and detection of vascular disease. With SSFP MR angiography, 39 of 41 renal arteries in 19 patients were correctly detected. Relevant stenoses were correctly identified with SSFP MR angiography in two patients. In two patients, SSFP MR angiographic data sets led to false-positive overgrading of vascular disease. Fast breath-hold 3D SSFP MR angiography appears to be feasible for MR angiography of renal arteries.     

MR angiography with superparamagnetic iron oxide: feasibility study.

Magnetic resonance (MR) angiography with blood-pool superparamagnetic iron oxide (SPIO) particles was evaluated in the whole-body vascular system. In 12 adult patients, three-dimensional fast imaging with steady-state precession was performed in successive steps from the lungs to the calves before and after a standard dose for liver imaging (15 mumol of iron per kilogram of body weight) of AMI-25. On SPIO-enhanced MR angiograms, visualization of the pulmonary arterial, whole-body, and lower extremity venous systems was graded as good or sufficient in all patients, and femoral vein thrombosis was clearly demonstrated in one patient.