Petrice M. Mostardi

Controlled experimental study depicting moving objects in view-shared time-resolved 3D MRA

Various methods have been used for time‐resolved contrast‐enhanced magnetic resonance angiography (CE‐MRA), many involving view sharing. However, the extent to which the resultant image time series represents the actual dynamic behavior of the contrast bolus is not always clear. Although numerical simulations can be used to estimate performance, an experimental study can allow more realistic characterization. The purpose of this work was to use a computer‐controlled motion phantom for study of the temporal fidelity of three‐dimensional (3D) time‐resolved sequences in depicting a contrast bolus. It is hypothesized that the view order of the acquisition and the selection of views in the reconstruction can affect the positional accuracy and sharpness of the leading edge of the bolus and artifactual signal preceding the edge. Phantom studies were performed using dilute gadolinium‐filled vials that were moved along tabletop tracks by a computer‐controlled motor. Several view orders were tested using view‐sharing and Cartesian sampling. Compactness of measuring the k‐space center, consistency of view ordering within each reconstruction frame, and sampling the k‐space center near the end of the temporal footprint were shown to be important in accurate portrayal of the leading edge of the bolus. A number of findings were confirmed in an in vivo CE‐MRA study. Magn Reson Med, 2009.

High temporal and spatial resolution 3D time-resolved contrast-enhanced magnetic resonance angiography of the hands and feet

Methods are described for generating 3D time‐resolved contrast‐enhanced magnetic resonance (MR) angiograms of the hands and feet. Given targeted spatial resolution and frame times, it is shown that acceleration of about one order of magnitude or more is necessary. This is obtained by a combination of 2D sensitivity encoding (SENSE) and homodyne (HD) acceleration methods. Image update times from 3.4–6.8 seconds are provided in conjunction with view sharing. Modular receiver coil arrays are described which can be designed to the targeted vascular region. Images representative of the technique are generated in the vasculature of the hands and feet in volunteers and in patient studies. J. Magn. Reson. Imaging 2011;.

Estimating T1 from multichannel variable flip angle SPGR sequences

Quantitative estimation of T1 is a challenging but important task inherent to many clinical applications. The most commonly used paradigm for estimating T1 in vivo involves performing a sequence of spoiled gradient‐recalled echo acquisitions at different flip angles, followed by fitting of an exponential model to the data. Although there has been substantial work comparing different fitting methods, there has been little discussion on how these methods should be applied for data acquired using multichannel receivers. In this note, we demonstrate that the manner in which multichannel data is handled can have a substantial impact on T1 estimation performance and should be considered equally as important as choice of flip angles or fitting strategy. Magn Reson Med, 2013.

Max CAPR: High‐resolution 3D contrast‐enhanced MR angiography with acquisition times under 5 seconds

High temporal and spatial resolution is desired in imaging of vascular abnormalities having short arterial‐to‐venous transit times. Methods that exploit temporal correlation to reduce the observed frame time demonstrate temporal blurring, obfuscating bolus dynamics. Previously, a Cartesian acquisition with projection reconstruction‐like (CAPR) sampling method has been demonstrated for three‐dimensional contrast‐enhanced angiographic imaging of the lower legs using two‐dimensional sensitivity‐encoding acceleration and partial Fourier acceleration, providing 1mm isotropic resolution of the calves, with 4.9‐sec frame time and 17.6‐sec temporal footprint. In this work, the CAPR acquisition is further undersampled to provide a net acceleration approaching 40 by eliminating all view sharing. The tradeoff of frame time and temporal footprint in view sharing is presented and characterized in phantom experiments. It is shown that the resultant 4.9‐sec acquisition time, three‐dimensional images sets have sufficient spatial and temporal resolution to clearly portray arterial and venous phases of contrast passage. It is further hypothesized that these short temporal footprint sequences provide diagnostic quality images. This is tested and shown in a series of nine contrast‐enhanced MR angiography patient studies performed with the new method. Magn Reson Med, 2010.

Recovery of phase inconsistencies in continuously moving table extended field of view magnetic resonance imaging acquisitions

MR images formed using extended FOV continuously moving table data acquisition can have signal falloff and loss of lateral spatial resolution at localized, periodic positions along the direction of table motion. In this work we identify the origin of these artifacts and provide a means for correction. The artifacts are due to a mismatch of the phase of signals acquired from contiguous sampling fields of view and are most pronounced when the central k‐space views are being sampled. Correction can be performed using the phase information from a periodically sampled central view to adjust the phase of all other views of that view cycle, making the net phase uniform across each axial plane. Results from experimental phantom and contrast‐enhanced peripheral MRA studies show that the correction technique substantially eliminates the artifact for a variety of phase encode orders. Magn Reson Med, 2005.

High Temporal and Spatial Resolution Imaging of Peripheral Vascular Malformations

To assess the performance of a recently developed 3D time‐resolved CE‐MRA technique, Cartesian Acquisition with Projection‐Reconstruction‐like sampling (CAPR), for accurate characterization and treatment planning of vascular malformations of the periphery.

Contrast-enhanced MR Angiography of the Abdomen with Highly Accelerated Acquisition Techniques

PURPOSE To demonstrate that highly accelerated (net acceleration factor [R(net)] ≥ 10) acquisition techniques can be used to generate three-dimensional (3D) subsecond timing images, as well as diagnostic-quality high-spatial-resolution contrast material-enhanced (CE) renal magnetic resonance (MR) angiograms with a single split dose of contrast material. MATERIALS AND METHODS All studies were approved by the institutional review board and were HIPAA compliant; written consent was obtained from all participants. Twenty-two studies were performed in 10 female volunteers (average age, 47 years; range, 27-62 years) and six patients with renovascular disease (three women; average age, 48 years; range, 37-68 years; three men; average age, 60 years; range, 50-67 years; composite average age, 54 years; range, 38-68 years). The two-part protocol consisted of a low-dose (2 mL contrast material) 3D timing image with approximate 1-second frame time, followed by a high-spatial-resolution (1.0-1.6-mm isotropic voxels) breath-hold 3D renal MR angiogram (18 mL) over the full abdominal field of view. Both acquisitions used two-dimensional (2D) sensitivity encoding acceleration factor (R) of eight and 2D homodyne (HD) acceleration (R(HD)) of 1.4-1.8 for R(net) = R · R(HD) of 10 or higher. Statistical analysis included determination of mean values and standard deviations of image quality scores performed by two experienced reviewers with use of eight evaluation criteria. RESULTS The 2-mL 3D time-resolved image successfully portrayed progressive arterial filling in all 22 studies and provided an anatomic overview of the vasculature. Successful timing was also demonstrated in that the renal MR angiogram showed adequate or excellent portrayal of the main renal arteries in 21 of 22 studies. CONCLUSION Two-dimensional acceleration techniques with R(net) of 10 or higher can be used in CE MR angiography to acquire (a) a 3D image series with 1-second frame time, allowing accurate bolus timing, and (b) a high-spatial-resolution renal angiogram. SUPPLEMENTAL MATERIAL http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.11110242/-/DC1.

Prospective Comparison of Cartesian Acquisition with Projection-like Reconstruction Magnetic Resonance Angiography with Computed Tomography Angiography for Evaluation of below-the-Knee Runoff

PURPOSE To compare prospectively the assessment of stenosis and radiologist confidence in the evaluation of below-the-knee lower extremity runoff vessels between computed tomography (CT) angiography and contrast-enhanced magnetic resonance (MR) angiography in a cohort of 19 clinical patients. MATERIALS AND METHODS The study was compliant with the Health Insurance Portability and Accountability Act of 1996 and approved by the institutional review board. Imaging was performed in 19 consecutive patients with known or suspected peripheral arterial disease; both CT angiography and a more recently developed MR angiography technique were performed within 24 hours of each other and before any therapeutic intervention. Resulting images were randomized and interpreted in blinded fashion by four board-certified radiologists with expertise in CT angiography and MR angiography. Vasculature of the lower leg was apportioned into 22 segments, 11 for each leg. For each segment, degree of stenosis and confidence of diagnosis were determined using a 3-point scale. Differences between CT angiography and MR angiography were assessed for significance using pooled histograms that were analyzed using the Wilcoxon signed rank test. RESULTS For assessment of stenosis, there was no difference in CT angiography compared with MR angiography for 20 of 22 segments. For confidence of diagnosis, assessment of popliteal arteries was superior on CT angiography compared with MR angiography (P<.05). Confidence in assessment of both tibioperoneal trunks and the left proximal anterior tibial artery was not significantly different between CT angiography and MR angiography. Confidence in assessment of all other 17 segments was superior with MR angiography compared with CT angiography (P<.02). CONCLUSIONS MR angiography using the method described here is a promising technique for evaluating lower extremity arterial runoff. MR angiography had an overall superior performance in radiologist confidence compared with CT angiography for imaging runoff vessels below the knee.

High spatial and temporal resolution imaging of the arterial vasculature of the lower extremity with contrast enhanced mr angiography

Vascular imaging can be essential in the diagnosis, monitoring, and planning and assessment of treatment of patients with peripheral vascular disease. The purpose of this work is to describe a recently developed three‐dimensional (3D) time‐resolved contrast‐enhanced MR angiography (CE‐MRA) technique, Cartesian Acquisition with Projection Reconstruction‐like sampling (CAPR), and its application to imaging of the vasculature of the lower legs and feet. CAPR implements accelerated imaging techniques and uses specialized multielement imaging coil arrays to achieve high temporal and high spatial resolution imaging. Volunteer and patient studies of the vasculature of the lower legs and feet have been performed. Temporal resolution of 4.9–6.5 sec and spatial resolution less than or equal to 1 mm in all directions allow for the depiction of progressive arterial filling and complex flow patterns as well as sharp visualization of vascular structure as small as the fine muscular branches. High‐quality diagnostic imaging is made possible with CAPRs advanced acquisition and reconstruction techniques and the use of specialized coil arrays. Clin. Anat. 24:478–488, 2011.

Time-Resolved, Contrast-Enhanced MR Angiography Using Cartesian Methods

Ever since the introduction of contrast-enhanced MR angiography in the mid-1990s, there has been steady improvement in the technique. Early investigations identified a number of performance targets, including the desirability for high-spatial-resolution 3D imaging, need to synchronize the acquisition to the arterial phase of the contrast bolus passage, and desirability for minimal enhancement of the venous system. To a great extent, these were addressed with the development of short repetition time (TR) gradient echo pulse sequences, nonreal-time and real-time means for determination of accurate timing, and development of centric view orders which allowed extended acquisition times into the venous phase.