Biomedical subjects

Kiaran P McGee

Publications and source records attributed to Kiaran P McGee.

7 recordsLinked to original sources

PubMed2006

MR angiography fusion technique for treatment planning of intracranial arteriovenous malformations.

PURPOSE: To develop an image fusion technique using elliptical centric contrast-enhanced (CE) MR angiography (MRA) and three-dimensional (3D) time-of-flight (TOF) acquisitions for radiosurgery treatment planning of arteriovenous malformations (AVMs). MATERIALS AND METHODS: CE and 3D-TOF MR angiograms with disparate in-plane fields of view (FOVs) were acquired, followed by k-space reformatting to provide equal voxel dimensions. Spatial domain addition was performed to provide a third, fused data volume. Spatial distortion was evaluated on an MRA phantom and provided slice-dependent and global distortion along the three physical dimensions of the MR scanner. In vivo validation was performed on 10 patients with intracranial AVMs prior to their conventional angiogram on the day of gamma knife radiosurgery. RESULTS: Spatial distortion in the phantom within a volume of 14 x 14 x 3.2 cm(3) was less than +/-1 mm (+/-1 standard deviation (SD)) for CE and 3D-TOF data sets. Fused data volumes were successfully generated for all 10 patients. CONCLUSION: Image fusion can be used to obtain high-resolution CE-MRA images of intracranial AVMs while keeping the fiducial markers needed for gamma knife radiosurgery planning. The spatial fidelity of these data is within the tolerance acceptable for daily quality control (QC) purposes and gamma knife treatment planning.

Adult↗

PubMed2006

Myocardial tagging and strain analysis at 3 Tesla: comparison with 1.5 Tesla imaging.

PURPOSE: To determine whether imaging at 3 T could improve and prolong the tag contrast compared to images acquired at 1.5 T in normal volunteers, and whether such improvement would translate into the ability to perform strain measurements in diastole. MATERIALS AND METHODS: Normal volunteers (N = 13) were scanned at 1.5 T (GE Signa CV/i) and 3.0 T (GE VH/i). An ECG-triggered, segmented k-space, spoiled-gradient-echo grid-tagged sequence was used during cine acquisition. Tag contrast was determined by the difference of the mean signal intensity (SI) of the tagline to the mean SI of the myocardium divided by the standard deviation (SD) of the noise (CNR(tag)). Matched short-axis (SA) slices were analyzed. Strain measurements were performed on images using a 2D strain analysis software program (harmonic phase (HARP)). RESULTS: The average CNR(tag) over the cardiac cycle was superior at 3 T compared to 1.5 T for all slices (3 T: 23.4 +/- 12.1, 1.5 T: 9.8 +/- 8.4; P < 0.0001). This difference remained significant at cycle initiation, end-systole, and the end R-R interval (at cycle termination: 3 T = 14.0 +/- 11.0 vs. 1.5 T = 4.4 +/- 3.5; P < 0.01). Strain measures were obtainable only in early systole for 1.5 T images, but were robust throughout the entire R-R interval for 3 T images. CONCLUSION: Imaging at 3 T had a significant benefit for myocardial tag persistence through the cardiac cycle. The improvement allowed strain analysis to be performed into diastole.

Adult↗

PubMed2005

3 Tesla MR imaging provides improved contrast in first-pass myocardial perfusion imaging over a range of gadolinium doses.

PURPOSE: To compare myocardial enhancement during first-pass myocardial perfusion imaging at 3.0 Tesla (T) and 1.5T. MATERIALS AND METHODS: First-pass myocardial perfusion imaging was performed on twelve normal subjects at 3T and 1.5T using an interleaved notched saturation recovery gradient echo pulse sequence. Subjects received either 0.10 mmol/kg for both scans (group 1), 0.075 mmol/kg for both scans (group 2), or 0.075 mmol/kg for the 3T scan and 0.10 mmol/kg for the 1.5T scan (group 3). RESULTS: Contrast enhancement was significantly greater at 3T than at 1.5T for the 12 subjects whether enhancement was normalized to baseline signal intensity (2.58 +/- 0.76 vs. 1.52 +/- 0.37, p < 0.0001) or to noise (57.6 +/- 19.7 vs. 14.7 +/- 7.8, p < 0001). For each of the three groups, contrast enhancement was significantly greater at 3T versus 1.5T (p < 0.0001, p < 0.001, p < 0.008 when normalized to baseline signal; p < 0.0001 for all groups when normalized to noise). CONCLUSION: 3T improves contrast in first-pass myocardial perfusion imaging at either 0.10 mmol/kg or 0.075 mmol/kg.

Adult↗

PubMed2004

Cardiac magnetic resonance parallel imaging at 3.0 Tesla: technical feasibility and advantages.

PURPOSE: To quantify changes in signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), specific absorption rate (SAR), RF power deposition, and imaging time in cardiac magnetic resonance imaging with and without the application of parallel imaging at 1.5 T and 3.0 T. MATERIALS AND METHODS: Phantom and volunteer data were acquired at 1.5 T and 3.0 T with and without parallel imaging. RESULTS: Doubling field strength increased phantom SNR by a factor of 1.83. In volunteer data, SNR and CNR values increased by factors of 1.86 and 1.35, respectively. Parallel imaging (reduction factor = 2) decreased phantom SNR by a factor of 1.84 and 2.07 when compared to the full acquisition at 1.5 T and 3.0 T, respectively. In volunteers, SNR and CNR decreased by factors of 2.65 and 2.05 at 1.5 T and 1.99 and 1.75 at 3.0 T, respectively. Doubling the field strength produces a nine-fold increase in SAR (0.0751 to 0.674 W/kg). Parallel imaging reduced the total RF power deposition by a factor of two at both field strengths. CONCLUSIONS: Parallel imaging decreases total scan time at the expense of SNR and CNR. These losses are compensated at higher field strengths. Parallel imaging is effective at reducing total power deposition by reducing total scan time.

Adult↗

PubMed2002

Wrist: improved MR imaging with optimized transmit-receive coil design.

The optimized wrist coil was designed and built as a transmit-receive birdcage coil for 1.5-T magnetic resonance (MR) imaging. Phantom studies were conducted to compare the optimized design with custom-designed and commercially available phased-array wrist coils and showed a 50%-90% improvement in signal-to-noise ratio (SNR). Blinded review of wrist images obtained in six volunteers showed that the optimized birdcage coil was preferred in 75% of the comparisons. An optimized birdcage coil designed for wrist imaging has improved both SNR and uniformity compared with those with a phased-array coil with the same geometry.

Adult↗

PubMedDate not supplied

Motion-correction techniques for standing equine MRI.

Magnetic resonance imaging (MRI) of the distal extremities of the standing, sedated horse would be desirable if diagnostic quality images could be obtained. With the availability of extremity and special purpose magnet designs on the market, a system to safely accommodate the standing horse may gain increasing popularity. This paper considers the issue of motion that will need to be addressed to achieve successful, diagnostic quality images. The motion of the carpus and tarsus of five standing, sedated horses was quantified. The obtained motion records were then used to induce motion in cadaveric joint specimens during several MRI scans. The measured dorsal-palmar/plantar, medial-lateral, and proximal-distal random wobbling motions in the standing sedated horse were several centimeters in magnitude and generated severe motion-artifacts during axial MRI of the cadaveric specimens. Two retrospective motion-correction techniques (autocorrection and navigator-based adaptive correction) were used to correct the corrupted images. The motion artifacts were nearly eliminated with the use of both techniques in series. Although significant hurdles remain, these results suggest promise for allowing diagnostic quality MRI of the carpus and tarsus in the standing horse.

Animals↗

PubMedDate not supplied

Evaluation of cardiac valvular disease with MR imaging: qualitative and quantitative techniques.

Magnetic resonance (MR) imaging is almost never performed as the initial imaging test in cardiac valvular disease; that role is dominated by echocardiography. Nevertheless, MR imaging has much to offer in selected patients. Quantitative information regarding the severity of regurgitant or stenotic lesions can be obtained by using a combination of cine gradient-echo or steady-state free precession and cine phase-contrast sequences. In addition to providing measurements of peak velocity and flow, MR imaging is the standard of reference for evaluation of ventricular function, which can be a critical factor in determining when surgical intervention is indicated. Improvements in cardiac MR imaging technology have been particularly striking in the past few years, and these developments can easily be applied to the examination of cardiac valves. The authors briefly describe the pathophysiology of valvular disease, discuss standard MR techniques for qualitative and quantitative evaluation of valvular lesions, and illustrate these concepts with several case studies.

Heart Valve Diseases↗