Biomedical subjects

C A Mistretta

Publications and source records attributed to C A Mistretta.

At least 19 recordsLinked to original sources

PubMed2006

High-resolution, time-resolved MRA provides superior definition of lower-extremity arterial segments compared to 2D time-of-flight imaging.

PURPOSE: To evaluate a novel time-resolved contrast-enhanced (CE) projection reconstruction (PR) magnetic resonance angiography (MRA) method for identifying potential bypass graft target vessels in patients with Class II-IV peripheral vascular disease. MATERIALS AND METHODS: Twenty patients (M:F = 15:5, mean age = 58 years, range = 48-83 years), were recruited from routine MRA referrals. All imaging was performed on a 1.5 T MRI system with fast gradients (Signa LX; GE Healthcare, Waukesha, WI). Images were acquired with a novel technique that combined undersampled PR with a time-resolved acquisition to yield an MRA method with high temporal and spatial resolution. The method is called PR hyper time-resolved imaging of contrast kinetics (PR-hyperTRICKS). Quantitative and qualitative analyses were used to compare two-dimensional (2D) time-of-flight (TOF) and PR-hyperTRICKS in 13 arterial segments per lower extremity. Statistical analysis was performed with the Wilcoxon signed-rank test. RESULTS: Fifteen percent (77/517) of the vessels were scored as missing or nondiagnostic with 2D TOF, but were scored as diagnostic with PR-hyperTRICKS. Image quality was superior with PR-hyperTRICKS vs. 2D TOF (on a four-point scale, mean rank = 3.3 +/- 1.2 vs. 2.9 +/- 1.2, P < 0.0001). PR-hyperTRICKS produced images with high contrast-to-noise ratios (CNR) and high spatial and temporal resolution. 2D TOF images were of inferior quality due to moderate spatial resolution, inferior CNR, greater flow-related artifacts, and absence of temporal resolution. CONCLUSION: PR-hyperTRICKS provides superior preoperative assessment of lower limb ischemia compared to 2D TOF.

Aged↗

PubMed2006

Highly constrained backprojection for time-resolved MRI.

Recent work in k-t BLAST and undersampled projection angiography has emphasized the value of using training data sets obtained during the acquisition of a series of images. These techniques have used iterative algorithms guided by the training set information to reconstruct time frames sampled at well below the Nyquist limit. We present here a simple non-iterative unfiltered backprojection algorithm that incorporates the idea of a composite image consisting of portions or all of the acquired data to constrain the backprojection process. This significantly reduces streak artifacts and increases the overall SNR, permitting decreased numbers of projections to be used when acquiring each image in the image time series. For undersampled 2D projection imaging applications, such as cine phase contrast (PC) angiography, our results suggest that the angular undersampling factor, relative to Nyquist requirements, can be increased from the present factor of 4 to about 100 while increasing SNR per individual time frame. Results are presented for a contrast-enhanced PR HYPR TRICKS acquisition in a volunteer using an angular undersampling factor of 75 and a TRICKS temporal undersampling factor of 3 for an overall undersampling factor of 225.

Algorithms↗

PubMed2004

Artifact reduction in undersampled projection reconstruction MRI of the peripheral vessels using selective excitation.

The projection reconstruction (PR)-HyperTRICKS (time resolved imaging of contrast kinetics) acquisition integrates the benefits of through-plane Cartesian slice encoding and in-plane undersampled PR. It provides high spatial resolution both in-plane (about 1 mm(2)) and through-plane (1-2 mm), as well as relatively high temporal resolution (about 0.25 frames per second). However, undersampling artifacts that originate from anatomy superior or inferior to a coronal imaging FOV may severely degrade the image quality. In coronal MRA acquisitions, the slice coverage is limited in order to achieve high temporal resolution. In this report we describe an artifact reduction method that uses selective excitation in PR-HyperTRICKS. This technique significantly reduces undersampling streak artifacts while it increases the slice coverage.

Artifacts↗

PubMed2004

High-resolution multistation peripheral MR angiography using undersampled projection reconstruction imaging.

A novel protocol for three-station MR angiography (MRA) of the lower extremities is described. A time-resolved undersampled projection reconstruction (PR) acquisition was used to image the calf station during a first injection, and non-time-resolved PR acquisitions were used with the bolus-chase technique to image the abdomen and thigh stations during a second injection. The streak artifacts resulting from undersampling the PR data were reduced with the use of a spatial Fermi filter based on the sensitivity of each coil element in a peripheral vascular phased-array coil. This novel technique provided high spatial resolution and a broad range of coverage, and depicted the contrast dynamics in the most distal station of the lower extremities.

Abdomen↗

PubMed2003

SNR improvement for multiinjection time-resolved high-resolution CE-MRA of the peripheral vasculature.

Peripheral MR angiography (MRA) should ideally provide images over a large field of view with high spatial resolution and adequate temporal resolution to accommodate differences in regional filling times. Image subtraction is usually used to remove background signals. In examination protocols involving multiple injections at multiple sites, previously injected contrast present in the mask image provides a substantial decrease in the subtraction image signal. Bolus chase methods avoid this problem but provide limited time for acquisition of high-resolution images at each station. We present here a technique applied to peripheral angiography that provides high spatial and temporal resolution while maintaining high SNR in multiple injection examinations. Undersampled projection imaging was used to increase spatial resolution relative to a previously reported technique using a Cartesian acquisition technique. Late acquisition of high spatial frequencies and temporal matched-filtering were used to increase spatial resolution and SNR, respectively. Temporal correlation analysis was applied to permit multistation examinations without mask subtraction, thus providing an additional gain in SNR relative to multistation subtraction methods. Quantitative analysis is provided to evaluate the signal and noise behavior in the matched-filtering process due to multiinjection and mask subtraction.

Computer Simulation↗

PubMed2002

Time-resolved, undersampled projection reconstruction imaging for high-resolution CE-MRA of the distal runoff vessels.

Imaging of the blood vessels below the knee using contrast-enhanced (CE) MRI is challenging due to the need to coordinate image acquisition and arrival of the contrast in the targeted vessels. Time-resolved acquisitions have been successful in consistently capturing images of the arterial phase of the bolus of contrast agent in the distal extremities. Although time-resolved exams are robust in this respect, higher spatial resolution for the depiction of tight stenoses and the small vessels in the lower leg is desirable. A modification to a high-spatial-resolution T(1)-weighted pulse sequence (projection reconstruction-time resolved imaging of contrast kinetics (PR-TRICKS)) that improves the through-plane spatial resolution by a factor of 2 and maintains a high frame rate is presented. The undersampled PR-TRICKS pulse sequence has been modified to double the spatial resolution in the slice direction by acquiring high-spatial-frequency slice data only after first pass of the bolus of contrast agent. The acquisition reported in the present work (PR-hyperTRICKS) has been used to image healthy volunteers and patients with known vascular disease. The temporal resolution was found to be beneficial in capturing arterial phase images in the presence of asymmetric filling of vessels.

Contrast Media↗

PubMed2001

The effect of injection rate on time-resolved contrast-enhanced peripheral MRA.

In contrast-enhanced (CE) magnetic resonance (MR) angiography (MRA), lower injection rates of a fixed contrast agent dose provide longer contrast agent bolus at the expense of lower intravascular signal. This study evaluated the effect of different injection rates in imaging of the vasculature of the lower extremities with time-resolved, CE MRA. In three volunteers, injection rates of 0.5, 1.5 and 3.0 mL/second were administered in a randomized order and imaged in two separate sessions. Contrast agent bolus dynamics measured in volunteers were used in computer simulations to confirm variations in contrast agent concentration as a source of vessel ringing and blurring artifacts. To validate the effect of injection rate in pathologic vessels, 37 patients with peripheral vascular disease were imaged with a time-resolved technique using an injection rate of 0.5 mL/second or 1.5 mL/second and retrospectively divided into two groups. In volunteers, higher injection rates caused a stronger modulation of k-space and resulted in increased ringing artifacts in time-resolved CE MRA. These results were reproduced with computer simulations. In the qualitative patient study, significantly less vessel blurring was observed using a lower injection-rate, without a significant loss of vessel contrast.

Adult↗

PubMed2001

Contrast-Enhanced magnetic resonance angiography of the carotid bifurcation using the time-resolved imaging of contrast kinetics (TRICKS) technique.

The time-resolved contrast-enhanced magnetic resonance (MR) angiographic technique TRICKS (time-resolved imaging of contrast kinetics) reconstructs a temporal series of three-dimensional (3D) images. The temporal resolution is increased by using a short TR (<8 ms) and TE (<2 ms), zero filling, partial echo sampling, view sharing, and temporally sampling k-space at variable rates. TRICKS allows reconstruction of multiple sequential 3D volumes following bolus injection of a gadolinium chelate (0.2 mmol/kg body weight up to 40 ml, injection rate -2 ml/s). The resulting temporally defined datasets are conceptually similar to a catheter-based intra-arterial digital subtraction angiographic series, except that they are 3D volumes and not projection images. Similar to other contrast-enhanced MR angiographic methods, TRICKS improves delineation of carotid artery stenosis by minimizing saturation effects. TRICKS and other contrast-enhanced MR angiographic techniques use short echo times and small voxels, thus reducing intravoxel dephasing. Surface morphology of atherosclerotic plaque and slow flow in nearly occluded vessels ("string sign") are well delineated. The major advantage of the TRICKS technique is that the timing of the acquisition in relation to the passage of the contrast bolus occurs automatically, allowing for consistent capture of the arterial phase. and eliminating the need for sophisticated synchronization methods.

Carotid Arteries↗

PubMed2001

Aorta and runoff vessels: single-injection MR angiography with automated table movement compared with multiinjection time-resolved MR angiography--initial results.

The authors compared two techniques for performing runoff, contrast material-enhanced magnetic resonance (MR) angiography. Multiinjection time-resolved imaging of contrast kinetics (TRICKS) and single-injection bolus-chase MR angiographic examinations were performed in 10 volunteers and 10 patients. Image quality and venous overlay of the major blood vessels of the abdomen, thigh, and calf were evaluated. Significantly more (P <.05) vessels were depicted with diagnostic quality on multiinjection TRICKS than on single-injection bolus-chase MR angiographic images.

Adult↗

PubMed2000

Undersampled projection reconstruction applied to MR angiography.

Undersampled projection reconstruction (PR) is investigated as an alternative method for MRA (MR angiography). In conventional 3D Fourier transform (FT) MRA, resolution in the phase-encoding direction is proportional to acquisition time. Since the PR resolution in all directions is determined by the readout resolution, independent of the number of projections (Np), high resolution can be generated rapidly. However, artifacts increase for reduced Np. In X-ray CT, undersampling artifacts from bright objects like bone can dominate other tissue. In MRA, where bright, contrast-filled vessels dominate, artifacts are often acceptable and the greater resolution per unit time provided by undersampled PR can be realized. The resolution increase is limited by SNR reduction associated with reduced voxel size. The hybrid 3D sequence acquires fractional echo projections in the k(x)-k(y) plane and phase encodings in k(z). PR resolution and artifact characteristics are demonstrated in a phantom and in contrast-enhanced volunteer studies.

Artifacts↗

PubMed2000

Undersampled projection-reconstruction imaging for time-resolved contrast-enhanced imaging.

In time-resolved contrast-enhanced 3D MR angiography, spatial resolution is traded for high temporal resolution. A hybrid method is presented that attempts to reduce this tradeoff in two of the spatial dimensions. It combines an undersampled projection acquisition in two dimensions with variable rate k-space sampling in the third. Spatial resolution in the projection plane is determined by readout resolution and is limited primarily by signal-to-noise ratio. Oversampling the center of k-space combined with temporal k-space interpolation provides time frames with minimal venous contamination. Results demonstrating improved resolution in phantoms and volunteers are presented using angular undersampling factors up to eight with acceptable projection reconstruction artifacts.

Abdomen↗

PubMed2000

Phase-contrast with interleaved undersampled projections.

MR phase-contrast techniques provide velocity-sensitive angiograms and quantitative flow measurements but require long scan times. Recently it has been shown that undersampled projection reconstruction can acquire higher resolution per unit time than Fourier techniques with acceptable artifacts when used in contrast-enhanced MR angiography. Undersampled projection reconstruction has similar potential for phase-contrast acquisitions. Flow sensitization gradients are used with projection trajectories to acquire velocity-dependent phase information. An acquisition scheme that acquires three flow encoding directions on three sets of angular-interleaved projections is introduced. Depending on the resolution, acquisition times for 3D datasets can decrease by factors of two to four.

Artifacts↗

PubMed2000

3D MR DSA: effects of injection protocol and image masking.

The purpose of this study was to investigate the effect on three-dimensional (3D) magnetic resonance digital subtraction angiography (MR DSA) images of various injection protocol parameters (ie, injection order, volume, and rate), as well as image masking. The pelves of 10 normal volunteers were scanned using seven different contrast agent volume/injection rate combinations. Subtraction of a precontrast mask image resulted in vascular image contrast improvements of between 4.0 and 7.7 times. Image quality and smaller vessel image contrast in the masked data decreased with increasing injection number. Data acquired with a high (0.150 mmol kg(-1)) volume yielded the highest quality images, although only small nonsignificant differences in image quality and large vessel conspicuity were found between images obtained using the high and medium (0.075 mmol kg(-1)) volumes. Images acquired with a low (0. 038 mmol kg(-1)) volume, while of lower image contrast, were judged to be of reasonable quality, especially when acquired as the first or second injection. Injection rate (1 ml s(-1), 2 ml s(-1), and 4 ml s(-1)) was not found to affect the images significantly, although selection of an injection rate that gave an injection duration of approximately 10 seconds tended to give better vascular image contrast. Based on these data, a series of escalating volumes for multi-injection examination is proposed. J. Magn. Reson. Imaging 2000;12:476-487.

Adult↗

PubMed2000

Method for rapidly determining and reconstructing the peak arterial frame from a time-resolved CE-MRA exam.

A method that determines the information necessary to reconstruct a single vascular image from a time-resolved CE-MRA exam is presented. Raw k-space data are used to approximate the time course of the contrast passage prior to image reconstruction. The resulting k-space contrast curve is used to select the data corresponding to peak arterial enhancement. These data are reconstructed and immediately presented for physician review, with the entire time-series of images available at a later time for more detailed diagnosis. This approach dramatically reduces the latency between acquisition of large 4D (3D plus time) data sets and presentation of a diagnostic quality time frame. This algorithm has proven successful in the imaging of several anatomical regions and-in exams that do not require a breath hold-permits the use of an acquisition method that produces a contrast-enhanced angiogram without a timing scan.

Arteries↗

PubMed2000

Single breath-hold 3D contrast-enhanced method for assessment of cardiac function.

Cardiac MRI function measurements are typically performed using 2D sequences and require multiple breath-holds to image the entire heart. A single 3D acquisition using a T(1)-shortening agent has many potential advantages over techniques that acquire multiple 2D images, including more consistent contrast and precise slice coverage. However, 3D techniques currently require much longer than a single breath-hold to complete. It has been shown that for MR angiography undersampled projection reconstruction can acquire much higher resolution per unit time than Fourier imaging with acceptable artifacts. By employing a gated, undersampled projection technique, high-resolution 3D multiphase volumes of the heart can be acquired in a single breath-hold. Short repetition times result in good myocardial suppression and a temporal aperture of 60 ms.

Contrast Media↗

PubMed2000

Real-time MR imaging-guided passive catheter tracking with use of gadolinium-filled catheters.

PURPOSE: To test the hypothesis that real-time magnetic resonance (MR) imaging-guided passive catheter tracking is feasible with use of dilute gadolinium (Gd)-filled catheters, to determine the optimal Gd concentration required for tracking, and to measure catheter tip tracking accuracy. MATERIALS AND METHODS: The authors tested a real-time, T1-weighted, two-dimensional, spoiled gradient-recalled echo MR imaging sequence suitable for tracking catheters. In a yogurt phantom, the authors placed 5-F catheters filled with 2%-12% Gd solutions. MR imaging was performed with and without use of a projection dephaser that suppressed background signal. The authors measured signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and enhancement ratio to determine the optimal Gd concentration for catheter depiction. Catheter tip tracking accuracy was measured in an acrylic phantom with use of linear regression analysis, with goodness of fit assessed statistically with the F test. RESULTS: Peak catheter SNR, CNR, and enhancement ratios were obtained with 4%-6% Gd concentrations. Tip tracking accuracy was determined to be +/- 0.41 mm (R2 = 0.99; P < .0001). MR imaging reconstructions were displayed up to 3.1 frames/sec. CONCLUSIONS: Accurate MR imaging-guided passive catheter tracking was feasible in real-time with use of dilute Gd-filled catheters. This technique may have application in MR imaging-guided endovascular procedures.

Catheterization↗

PubMed2000

MR-guided angioplasty of renal artery stenosis in a pig model: a feasibility study.

PURPOSE: To test the hypothesis that magnetic resonance (MR) imaging can guide the percutaneous treatment of renal artery stenosis in a pig model. MATERIALS AND METHODS: Ameroid constrictors were surgically placed around six renal arteries in four pigs. After 30-36 days, all stenoses were documented by conventional x-ray aortograms. MR-guided renal angioplasty was attempted for three stenoses. For these pigs, MR angiography was performed with use of contrast-enhanced three-dimensional (3D) techniques. The authors visualized catheters by filling them with dilute 4% gadolinium and imaging with two-dimensional (2D) and 3D MR fast spoiled gradient recalled echo techniques. Under MR guidance, the authors advanced a selective catheter into the affected renal artery and crossed the stenosis with a nitinol guide wire. Angioplasty was performed with a balloon catheter filled with dilute gadolinium. Stenosis and luminal diameter measurements were compared before and after angioplasty. RESULTS: After ameroid constrictor placement, four significant stenoses, one mild stenosis, and one occlusion developed. Under MR guidance, the authors achieved technical success in performing three of three (100%) attempted dilations. After MR-guided angioplasty, the mean reduction in stenosis was 35% and the mean increase in luminal diameter was 1.6 mm. CONCLUSION: Use of MR guidance for the angioplasty of renal artery stenosis in pigs is feasible.

Angioplasty, Balloon↗

PubMed2000

Endovascular treatment of experimental canine aneurysms: feasibility with MR imaging guidance.

PURPOSE: To evaluate the feasibility of using magnetic resonance (MR) imaging to guide and monitor endovascular therapeutic procedures. MATERIALS AND METHODS: Endovascular therapeutic procedures were performed with MR imaging guidance in eight dogs by using a 1.5-T MR unit with echo-planar imaging capabilities. Carotid arterial aneurysms were surgically created in four dogs. The ability to depict, track, and position catheters, guide wires, and Guglielmi detachable coils was assessed. Catheters were first positioned with fluoroscopic guidance. Tracking and depiction were achieved with MR imaging by using commercially available catheters filled with a gadopentetate dimeglumine solution and a fast, two-dimensional, time-resolved, variable-rate k-space sampling technique. RESULTS: When either a catheter or the coaxial space between a catheter and a guide wire was filled with a solution of gadopentetate dimeglumine, catheter movement was always depicted. In the animals with aneurysms, it was possible to depict movement of a catheter into and out of the aneurysm. This was achieved by superimposing reconstructed images obtained during catheter movement onto a previously acquired MR angiogram ("road map"). Prototype Guglielmi detachable coils were successfully positioned and detached. Aneurysm obliteration was monitored with the acquisition of new road map images. CONCLUSION: The results demonstrate the feasibility of using MR imaging to guide endovascular therapeutic procedures.

Aneurysm↗