Biomedical subjects

S B Fain

Publications and source records attributed to S B Fain.

17 recordsLinked to original sources

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↗

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

Effect of windowing and zero-filled reconstruction of MRI data on spatial resolution and acquisition strategy.

Standard, MR spin-warp sampling strategies acquire data on a rectangular k-space grid. That method samples data from the "corners" of k-space, i.e., data that lie in a region of k-space outside of an ellipse just inscribed in the rectangular boundary. Illustrative calculations demonstrate that the data in the corners of k-space contribute to the useful resolution only if an interpolation method such as a zero-filled reconstruction is used. The consequences of this finding on data acquisition and data windowing strategies are discussed. A further implication of this result is that the spatial resolution of images reconstructed with zero-filling (but without radial windowing) is expected to display angular dependence, even when the phase- and frequency-encoded resolutions are identical. This hypothesis is experimentally verified with a slit geometry phantom. It is also observed that images reconstructed without zero-filling do not display the angular dependence of spatial resolution predicted solely by the maximal k-space extent of the raw data. The implications of these results for 3D contrast-enhanced angiographic acquisitions with elliptical centric view ordering are explored with simulations.

Filtration↗

PubMed2001

Dependence of venous enhancement on the field of view in 3D contrast-enhanced MRA using the elliptical centric view order.

The dependence of venous suppression on the acquisition field of view (FOV) in elliptical centric 3D contrast-enhanced magnetic resonance angiography (CE-MRA) is studied theoretically and experimentally. It is hypothesized that a reduced FOV in an arterial phase acquisition results in improved venous suppression. An expression is derived linking the k-space representation of a vein to venous return time and acquisition parameters. For a y x z FOV reduction from 24 cm x 7.2 cm to 18 cm x 3.6 cm, equivalent voxel size, and venous return times ranging from 0-7 s, the mean improvement in venous suppression ranged from 7.0% for the 19-mm-diameter vein to 32.1% in the 6-mm-diameter vein, assuming a step function-shaped venous enhancement profile. Decreased venous enhancement with reduced FOV is also observed for scans with equivalent acquisition times, although the degree of suppression is dependent on the shape of the venous enhancement curve.

Carotid Artery, Common↗

PubMed2001

Embedded MR fluoroscopy: high temporal resolution real-time imaging during high spatial resolution 3D MRA acquisition.

A method termed "embedded fluoroscopy" for simultaneously acquiring a real-time sequence of 2D images during acquisition of a 3D image is presented. The 2D images are formed by periodically sampling the central phase encodes of the slab-select direction during the 3D acquisition. The tradeoffs in spatial and temporal resolution are quantified by two parameters: the "redundancy" (R), the fraction of the 3D acquisition sampled more than once; and the "effective temporal resolution" (T), the time between temporal updates of the central views. The method is applied to contrast-enhanced MR angiography (CE-MRA). The contrast bolus dynamics are portrayed in real time in the 2D image sequence while a high-resolution 3D image is being acquired. The capability of the 2D acquisition to measure contrast enhancement with only a 5% degradation of the spatial resolution of the 3D CE-MR angiogram is shown theoretically. The method is tested clinically in 15 CE-MRA patient studies of the carotid and renal arteries.

Feasibility Studies↗

PubMed2001

Carotid artery: elliptic centric contrast-enhanced MR angiography compared with conventional angiography.

PURPOSE: To determine the accuracy of elliptic centric contrast material-enhanced magnetic resonance (MR) angiography by using conventional angiography as the reference standard. MATERIALS AND METHODS: Fifty patients were examined prospectively with contrast-enhanced MR angiography and conventional angiography. The two examinations were performed within 1 week of each other. Two patients underwent conventional angiography of only one carotid artery, which yielded 98 arteries for comparison. RESULTS: With conventional angiography as the reference standard and by using a 70% threshold for internal carotid arterial diameter stenosis, maximum intensity projection (MIP) images had a sensitivity of 93.3%, specificity of 85.1%, and accuracy of 87.6%, whereas reformatted transverse source images had a sensitivity of 83.3%, specificity of 97.0%, and accuracy of 92.8%. Interobserver variability for conventional angiograms was 0.97, for MIP images was 0.91, and for source images was 0.90. The contrast-enhanced MR angiographic technique had a sensitivity of 88.9% and specificity of 58.1% for the presence of irregularity and/or ulceration. All 50 examinations were triggered appropriately so that minimal or no venous signal intensity was depicted. CONCLUSION: Contrast-enhanced elliptic centric three-dimensional MR angiography offers high-spatial-resolution, venous-suppressed images of the carotid arteries that appear to be adequate to replace conventional angiography in most patients examined prior to carotid endarterectomy.

Aged↗

PubMed2001

High-spatial-resolution contrast-enhanced MR angiography of the renal arteries: a prospective comparison with digital subtraction angiography.

PURPOSE: To evaluate a high-spatial-resolution three-dimensional (3D) contrast material-enhanced magnetic resonance (MR) angiographic technique for detecting proximal and distal renal arterial stenosis. MATERIALS AND METHODS: Twenty-five patients underwent high-spatial-resolution small-field-of-view (FOV) 3D contrast-enhanced MR angiography of the renal arteries, which was followed several minutes later by more standard, large-FOV 3D contrast-enhanced MR angiography that included the distal aorta and iliac arteries. For both acquisitions, MR fluoroscopic triggering and an elliptic centric view order were used. Two readers evaluated the MR angiograms for grade and hemodynamic significance of renal arterial stenosis, diagnostic quality, and presence of artifacts. MR imaging results for each patient were compared with those of digital subtraction angiograms. RESULTS: The high-spatial-resolution small-FOV technique provided high sensitivity (97%) and specificity (92%) for the detection of renal arterial stenosis, including all four distal stenoses encountered. The portrayal of the segmental renal arteries was adequate for diagnosis in 19 (76%) of 25 patients. In 12% of the patients, impaired depiction of the segmental arteries was linked to motion. CONCLUSION: The combined high-spatial-resolution small-FOV and large-FOV MR angiographic examination provides improved spatial resolution in the region of the renal arteries while maintaining coverage of the abdominal aorta and iliac arteries.

Aged↗

PubMed2000

Three-dimensional contrast-enhanced MR angiography with real-time fluoroscopic triggering: design specifications and technical reliability in 330 patient studies.

Technical reliability was determined for triggering three-dimensional (3D) contrast material-enhanced magnetic resonance (MR) angiography with MR fluoroscopy. Technical requirements for high reliability were also identified. Reliability was evaluated in 330 consecutive patient studies of the neck, thorax, abdomen, and pelvis. Contrast material arrival was detected fluoroscopically in 325 of the 330 studies (98.5%), and the 3D sequence was successfully triggered in 321 of 330 studies (97.3%). Fluoroscopic triggering of centrically encoded 3D MR angiographic acquisitions is a highly reliable means of obtaining 3D MR angiograms with high spatial resolution.

Abdomen↗

PubMed1999

Interactive three-point localization of double-oblique sections using MR fluoroscopy.

Magnetic resonance imaging allows significant freedom in selecting the orientation and position of a tomographic section. However, it can nonetheless be challenging to determine quickly and efficiently the correct parameters required to image a targeted anatomic structure that may lie at an oblique angle in the imaging volume. We describe a three-point tool in which a) the user interactively selects three points from an anatomic structure of interest during live MR fluoroscopy; b) adjustments to pulse sequence are calculated to image the tomographic section defined by the three points; and c) the section is then immediately imaged fluoroscopically. The tool allows quick localization of, for example, longitudinal images of specific arterial structures.

Algorithms↗

PubMed1999

A flexible view ordering technique for high-quality real-time 2DFT MR fluoroscopy.

A method to tailor the view order to the reconstruction cycle is introduced for real-time MRI. It is well known that view sharing and oversampling central k-space views can improve the temporal resolution of gradient-echo pulse sequences. By ordering phase-encodes to synchronize k-space acquisition with the reconstruction cycle, apparent temporal resolution can match the frame rate with as few as one-fourth of the phase-encodes sampled per reconstruction. Spatial resolution is maintained by periodically updating high spatial frequencies. In addition to apparent temporal resolution, three other criteria for real-time imaging are identified and evaluated: display latency, dispersion, and frame-to-frame consistency. Latency is minimized by ordering views in a reverse-centric manner within each reconstruction interval, sampling high-energy views immediately prior to beginning reconstruction. Dispersion is kept low and consistent by synchronizing acquisition and reconstruction, thus avoiding poorly timed reconstruction instances. Real-time implementation demonstrates pulsatile time-of-flight blood signal enhancement in humans.

Algorithms↗

PubMed1999

Theoretical limits of spatial resolution in elliptical-centric contrast-enhanced 3D-MRA.

The point spread function (PSF) for contrast-enhanced three-dimensional (3D) MR angiography using the elliptical centric view order is derived. This view order has been shown previously to provide high venous suppression thereby enabling long acquisition times capable of high spatial resolution. The dependence of the PSF on TR, field of view (FOV), scan time, and trigger time are shown explicitly. Theoretical predictions are corroborated with experimental results in phantoms and in vivo. The PSF width decreases as the square root of the product of TR and the two phase encoding FOV's for fixed nominal voxel size. The PSF peak amplitude increases as the reciprocal of this product. Theory and experiment demonstrate that acquisition times over 40 sec provide superior resolution compared to shorter acquisitions, despite falling levels of contrast agent concentration. The analysis predicts that an isotropic spatial resolution of 1 mm before zero filling is possible in a FOV large enough to encompass the carotid and vertebral arteries bilaterally. Magn Reson Med 42:1106-1116, 1999.

Carotid Arteries↗

PubMed1999

Real-time imaging and triggering of 3D contrast-enhanced MR angiograms using MR fluoroscopy.

Although a variety of timing techniques and data acquisition strategies have been used for three-dimensional contrast-enhanced MR angiography, many are still limited by inadequate overall reliability, limited spatial resolution, or complexity. A technique is presented in this work in which contrast arrival is detected in the targeted vasculature in real time using MR fluoroscopy. Upon detection the operator triggers a 3D MR angiographic acquisition which uses an elliptical centric view order. It is shown that the view order intrinsically provides a high degree of venous suppression which in turn allows acquisition times of 30 s or longer, permitting high spatial resolution. The reliability of fluoroscopic triggering in bolus detection is shown to be over 90%. The technique provides high quality contrast-enhanced MR angiograms for many vascular regions.

Carotid Arteries↗

PubMed1999

3D contrast-enhanced MR angiography using fluoroscopic triggering and an elliptical centric view order.

Although a variety of timing techniques and data acquisition strategies have been used for three-dimensional contrast-enhanced MR angiography, many are still limited by inadequate overall reliability, limited spatial resolution, or complexity. A technique is presented in this work in which contrast arrival is detected in the targetted vasculature in real time using MR fluoroscopy. Upon detection the operator triggers a 3D MR angiographic acquisition which uses an elliptical centric view order. It is shown that the view order intrinsically provides a high degree of venous suppression which in turn allows acquisition times of 30 seconds or longer, permitting high spatial resolution. The reliability of fluoroscopic triggering in bolus detection is shown to be over 90%. The technique provides high quality contrast-enhanced MR angiograms for many vascular regions.

Fluoroscopy↗

PubMed1999

Carotid arteries: maximizing arterial to venous contrast in fluoroscopically triggered contrast-enhanced MR angiography with elliptic centric view ordering.

PURPOSE: To obtain high-spatial-resolution, venous-suppressed, contrast material-enhanced, three-dimensional (3D) magnetic resonance (MR) angiograms of the carotid arteries and aortic arch by using an elliptic centric view ordering with MR fluoroscopic triggering. MATERIALS AND METHODS: Forty consecutive patients with cerebrovascular disease in the differential diagnosis were evaluated with fluoroscopically triggered 3D MR angiography (gadoteridol dose range, 0.1-0.3 mmol per kilogram of body weight; mean acquisition time, 40 second +/- 8 [SD]). The contrast-enhanced 3D MR angiograms were evaluated for overall quality, vascular signal intensity, venous suppression, and motion artifact. Twenty patients also underwent two-dimensional (2D) time-of-flight (TOF) MR angiography. The overall quality of the 2D TOF MR angiograms and comparative quality between the 2D TOF and contrast-enhanced 3D MR angiograms were determined. RESULTS: The contrast-enhanced 3D MR angiograms were of excellent or more than adequate quality for diagnosis in 36 of the 40 studies (90%). In 35 of the 38 contrast-enhanced 3D studies in which the contrast material bolus was detected fluoroscopically, the internal jugular vein signal intensity was either not detectable or barely visible. In 18 of the 20 patients who also underwent 2D TOF MR angiography, the quality of the contrast-enhanced 3D MR angiograms was graded as markedly superior or superior. CONCLUSION: Contrast-enhanced, elliptic centric 3D MR angiography with real-time MR fluoroscopic triggering offers high-spatial-resolution images of the carotid arteries and aortic arch with reliable venous suppression.

Aorta, Thoracic↗

PubMed1992

Nursing care centers: a collaborative effort.

Nursing care centers evolved as a way to deliver health care as well as to bridge the gap between nursing education and nursing practice. This article defines the purposes of a nursing care center, and describes one such center developed by a large Southern university school of nursing, services it renders and the community's need for these services. The importance of collaborative practice in enhancing the success of nursing care centers is discussed.

Community Health Centers↗

PubMedDate not supplied

Optimizing dynamic T2* MR imaging for measurement of cerebral blood flow using infusions for cerebral blood volume.

We describe an approach to measuring cerebral blood flow (CBF) based on independent measurements of cerebral blood volume (CBV) and mean transit time (MTT) with calculation of CBF by using the central volume theorem: CBF = CBV / MTT. This permits optimization of the individual acquisitions and analyses. In particular, measurement of CBV during contrast infusion, rather than simultaneously with MTT from a single bolus, yields values more consistent with those of other methods.

Adult↗