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N J Pelc

Publications and source records attributed to N J Pelc.

At least 55 records · Page 3Linked to original sources
PubMed1994

Reconstructions of phase contrast, phased array multicoil data.

We present a reconstruction method for phased array multicoil data that is compatible with phase contrast MR angiography. The proposed algorithm can produce either complex difference or phase difference angiograms. Directional flow and quantitative information are preserved with the phase difference reconstruction. The proposed method is computationally efficient and avoids intercoil cancellation errors near the velocity aliasing boundary. Feasibility of the method is demonstrated on human scans.

Algorithms↗
PubMed1994

Magnetic resonance velocity imaging using a fast spiral phase contrast sequence.

Time-resolved velocity imaging using the magnetic resonance phase contrast technique can provide clinically important quantitative flow measurements in vivo but suffers from long scan times when based on conventional spin-warp sequences. This can be particularly problematic when imaging regions of the abdomen and thorax because of respiratory motion. We present a rapid phase contrast sequence based on an interleaved spiral k-space data acquisition that permits time-resolved, three-direction velocity imaging within a breath-hold. Results of steady and pulsatile flow phantom experiments are presented, which indicate excellent agreement between our technique and through plane flow measurements made with an in-line ultrasound probe. Also shown are results of normal volunteer studies of the carotids, renal arteries, and heart.

Blood Flow Velocity↗
PubMed1994

Single breath-hold pulmonary magnetic resonance angiography. Optimization and comparison of three imaging strategies.

RATIONALE AND OBJECTIVES: Ultrafast gradient-recalled-echo techniques for obtaining high-quality pulmonary magnetic resonance angiograms within a single breath-hold were optimized. METHODS: Fourteen subjects were imaged with both the body coil and a phased-array surface coil, using three gradient-recalled-echo pulse sequences: 1) two-dimensional sequential; 2) two-dimensional interleaved; and 3) volumetric acquisitions. Image quality was assessed with varied flip angle, receiver bandwidth, slice thickness/number, and matrix size. Cardiac compensation diminished ghost artifacts in the interleaved sequence. Individual sagittal sections and maximum intensity projections were reviewed. RESULTS: Pulmonary magnetic resonance angiograms acquired with volumetric and two-dimensional interleaved gradient-recalled-echo pulse sequences benefit greatest from intravenous gadolinium and result in greater pulmonary arterial visualization than traditional time-of-flight techniques. Phased-array coils result in improved vessel detection. CONCLUSIONS: High-quality breath-held pulmonary magnetic resonance angiography can be obtained with an intravenous contrast-enhanced gradient-recalled-echo acquisition; however, image quality is dependent on the pulse sequence.

Adult↗
PubMed1994

Evaluation of myocardial motion tracking with cine-phase contrast magnetic resonance imaging.

RATIONALE AND OBJECTIVES: The accuracy of myocardial motion measurements, computed from cine-phase contrast (cine-PC) magnetic resonance (MR) velocity data, was compared with directly visualized motion of MR signal voids caused by implanted tantalum markers in anesthetized dogs. METHODS: Magnetic resonance imaging (MRI) data were electrocardiogram-gated and divided into 16 phases per cardiac cycle. Myocardial trajectories as a function of time in the cardiac cycle were measured using both methods for four to seven markers in each of eight animals. RESULTS: The peak observed in-plane excursion was 4.0 +/- 2.1 mm. The average deviation between displacements derived from velocity data versus displacements visualized directly was 1.1 +/- 0.7 mm (27.5% of the peak displacement). The difference was less if three separate MR scans were used to measure each velocity component in the cine-PC method. This improvement is probably caused by improved temporal resolution. CONCLUSIONS: Cine-PC MRI offers a noninvasive method for accurate quantification of myocardial motion.

Animals↗
PubMed1994

Chronic mesenteric ischemia: evaluation with phase-contrast cine MR imaging.

PURPOSE: To compare superior mesenteric artery (SMA) blood flow in healthy volunteers and patients with stenoses in the fasting state and after food intake by using phase-contrast (PC) cine magnetic resonance (MR) imaging. MATERIALS AND METHODS: Ten healthy subjects, four asymptomatic patients (three with 50% stenosis, one with 70% stenosis), and one symptomatic patient (with 80% stenosis) were studied. All subjects were studied after fasting at least 8 hours and 15, 30, and 45 minutes after ingesting a standard meal. RESULTS: In healthy volunteers, SMA blood flow at all postprandial intervals increased significantly compared with that obtained after fasting (P < or = .0005). The percentage change in SMA blood flow 30 minutes after food intake provided the best distinction between the healthy subjects, the asymptomatic patients, and the symptomatic patient. CONCLUSION: Cine PC MR imaging is an effective, noninvasive technique for measuring SMA blood flow.

Adult↗
PubMed1994

Renal artery blood flow: quantitation with phase-contrast MR imaging with and without breath holding.

PURPOSE: To compare the accuracy of 16-frame cine phase-contrast (PC) magnetic resonance (MR) imaging with those of two breath-hold PC techniques in the measurement of renal artery blood flow. MATERIALS AND METHODS: In vitro flow measurements were performed in a segment of harvested human artery embedded in gel. For the cine PC acquisition, respiratory motion was simulated. In eight subjects with recently obtained para-amino-hippurate-clearance renal blood flow data, renal artery flow measurements were subsequently performed with two breath-hold imaging techniques and with cine PC imaging during shallow respiration. RESULTS: Breath-hold sequences were significantly more accurate than conventional cine PC sequences both in vitro (P < .005) and in vivo (P < .05). Cine PC imaging tended to overestimate flow (in vivo mean, 24.47% +/- 9.94), reflecting artifactual enlargement of the apparent vessel size. CONCLUSION: Reliable blood flow measurements in the renal artery are possible with breath-hold PC MR imaging.

Adult↗
PubMed1994

Shunt flow measurement and evaluation of valve oscillation with a spin-echo phase-contrast MR sequence.

PURPOSE: To present a spin-echo phase-contrast (SEPC) magnetic resonance pulse sequence designed to measure the very slow flow in ventricular shunt tubing. MATERIALS AND METHODS: A flow phantom constructed of shunt tubing and incorporating no valve or a high-, medium-, or low-pressure valve was connected to a flow pump. Flow rates were 0.05-1.00 mL/min (72-1,440 mL/d). Flow measurement was performed with the thin-section SEPC sequence. RESULTS: The flow rates measured with SEPC imaging correlated closely with the pump flow rate for the entire physiologic spectrum of shunt flow rates. This was true for all valves, resulting in overall R2s of .974 at 4 cm/sec and .980 at 2 cm/sec. Shunt flow was pulsatile with valves in place. There was a linear relationship between flow rate and the frequency of valve opening and closing. CONCLUSION: The SEPC technique is an accurate and noninvasive method of measuring shunt flow.

Cerebrospinal Fluid Shunts↗
PubMed1994

Elastic deformation in tendons and myotendinous tissue: measurement by phase-contrast MR imaging.

PURPOSE: To determine whether phase-contrast magnetic resonance (MR) imaging can be used to measure stretch in the myotendinous junction and tendon. MATERIALS AND METHODS: Velocity-encoded cine MR images obtained during cyclic motion were used to measure strain in myotendinous tissue and indirectly in tendons in gastrocnemius muscle-tendon sutured to a motion phantom. Videotapes of the experiments were digitized and used as a standard of reference for validation of MR measurements. Strain, rotation, and translation of the myotendinous junction were calculated from the phase-contrast MR data and indirectly in the tendon. RESULTS: Strain as determined from the MR imaging experiments agreed with the measurements from the video reference, with linear correlation coefficients of .987 for tendon strain and .992 for strain in the myotendinous junction. CONCLUSION: Measurement of tendon and myotendinous stretch during movement may provide insight into tendon ability to store energy and a means of noninvasive measurement of muscle force.

Animals↗
PubMed1994

Skeletal muscle contraction: analysis with use of velocity distributions from phase-contrast MR imaging.

PURPOSE: Velocity gradient data from phase-contrast magnetic resonance (MR) imaging were tested for the ability to calculate tensile strain and shear strain (deformation) during cyclical motion of skeletal muscle. MATERIALS AND METHODS: Strain data were derived from in vitro and in vivo phase-contrast MR velocity maps. A motion phantom designed to cyclically compress and expand a specimen of skeletal muscle provided a standard of reference to validate deformation, translation, and rotation measurements. The authors studied anterior and posterior muscle compartments of the lower extremity in three healthy volunteers during ankle dorsiflexion and plantar flexion against various resistances and the forearms of five healthy volunteers during flexion and extension of the fingers. RESULTS: The mean in vitro tracking error was 0.5 mm. The gastrocnemius muscle area in vivo changed 20% for both the minimum and maximum force conditions and therefore did not appear to be a good predictor of force. CONCLUSION: Phase-contrast MR imaging provides quantitative data on muscle contraction and demonstrates that shear and tensile strain can be measured and separated from translation and rotation of muscle.

Animals↗
PubMed1994

Magnetic resonance imaging evaluation of pulmonary vascular malformations.

OBJECTIVE: The purpose of our study was to establish magnetic resonance imaging (MRI) criteria for the diagnosis of pulmonary vascular malformations (PVMs). MATERIALS AND METHODS: Since 1987, 11 patients have been referred for chest MRI at our institution because of findings suggestive of a PVM. They were evaluated with a 1.5-T MRI system, incorporating a combination of spin-echo, gradient-recalled echo (GRE) cine, and 2-D phase contrast (PC) cine sequences. We used the following MRI criteria to diagnose PVM: (1) flow void or intermediate gray signal on spine-echo sequences; (2) bright signal on GRE cine sequences; and (3) bright signal consistent with flow detected on PC cine sequences using relatively low velocity ranges. Twelve patients not suspected of having a PVM served as controls; all had both MRI and pulmonary angiography to evaluate for central pulmonary embolus. RESULTS: Eight patients in the study group had PVM as determined with MRI using these criteria. In four of these patients, a PVM was confirmed by subsequent pulmonary angiography. Three patients did not have PVM utilizing these criteria; two had neoplasms and one had presumed mucus plugging and/or atelectasis that resolved spontaneously. The smallest vascular malformation detected by MRI was 1 cm. None of the control patients had PVM by MRI or pulmonary angiography. CONCLUSION: Utilizing these criteria, we believe that MRI is potentially an excellent noninvasive modality to evaluate PVM, and we stress that some form of PC cine sequence must be performed to determine if indeed there is blood flow within a suspicious lesion.

Adolescent↗
PubMed1994

Quantitative magnetic resonance flow imaging.

Time-of-flight and phase shift methods have both been used for vascular imaging with magnetic resonance. Phase methods, and phase contrast in particular, are well suited to quantitative measurements of velocity and volume flow rate. The most robust methods for measuring flow encode through-plane velocity into phase shift and compute flow by integrating the measured velocity over the vessel lumen. The accuracy of the flow data can be degraded by the effects of acceleration and eddy currents and by partial volume effects, including the effects of finite slice thickness and resolution, pulsatile waveforms, motion, and chemical shift. The reproducibility depends on the signal-to-noise of the data and the strength of the flow encoding and can be degraded by inconsistent definition of the vessel boundary. The adjustable flow sensitivity inherent in this method is a particular asset, allowing phase contrast flow measurement to operate over a dynamic range exceeding 10(5). Recently developed rapid imaging methods are helpful in applications that would be compromised by respiratory motion. With care, excellent quantitative data can be quickly obtained in vivo, and the resulting flow information is valuable for the diagnosis and management of a variety of conditions.

Humans↗
PubMed1994

Blood flow in major cerebral arteries measured by phase-contrast cine MR.

PURPOSE: To measure mean blood flow in individual cerebral arteries (carotid, basilar, anterior cerebral, middle cerebral, and posterior cerebral) using a cine phase contrast MR pulse sequence. METHODS: Ten healthy volunteers (22 to 38 years of age) were studied. The cine phase-contrast section was positioned perpendicular to the vessel of interest using oblique scanning planes. This pulse sequence used a velocity encoding range of 60 to 250 cm/sec. From the velocity and area measurements on the cine images, mean blood flow was calculated in milliliters per minute and milliliters per cardiac cycle. In the same subjects, transcranial Doppler measurements of blood velocity in these same vessels were also obtained. RESULTS: There was no difference in blood flow in the paired cerebral arteries. Carotid arteries had mean blood flow in the range of 4.8 +/- 0.4 ml/cycle, the basilar artery 2.4 +/- 0.2 ml/cycle, the middle cerebral artery 1.8 +/- 0.2 ml/cycle, the distal anterior cerebral artery 0.6 +/- 0.1 ml/cycle, and the posterior cerebral artery 0.8 +/- 0.1 ml/cycle. Overall, there was poor correlation between MR-measured and transcranial Doppler-measured peak velocity. CONCLUSION: Although careful attention to technical detail is required, mean blood flow measurements in individual cerebral vessels is feasible using a cine phase-contrast MR pulse sequence.

Adult↗
PubMed1994

Comparison of lesion enhancement on spin-echo and gradient-echo images.

PURPOSE: To compare lesion enhancement after injection of gadopentetate dimeglumine on spin-echo and gradient-echo T1-weighted images. METHODS: A total of 48 contrast-enhancing intracranial lesions were evaluated using a spin-echo and two gradient-echo T1-weighted pulse sequences. Percent contrast, contrast-to-noise, and signal-to-noise measurements were made on the spin-echo T1-weighted, three-dimensional gradient-echo, and multiplanar gradient-echo sequences. RESULTS: The measurements were somewhat different for the following categories of lesions: extraaxial, intraaxial with edema, and intraaxial without edema. The latter group provided the greatest diagnostic challenge: three of 19 such lesions 1 cm in size or smaller could not be identified on three-dimensional gradient-echo images, and one could not be identified on multi-planar gradient-echo images. The spin-echo T1-weighted sequence demonstrated significantly higher percent contrast (P < .05) and greater contrast to noise (P < .03) than either gradient-echo sequence for these small intraaxial lesions without edema. For extraaxial and intraaxial lesions with edema, percent C was similar for spin-echo T1-weighted and three-dimensional gradient-echo images, while contrast to noise was greater for spin-echo T1-weighted images. This reflected greater tissue noise with gradient-echo sequences. CONCLUSION: The T1-weighted spin-echo sequence was preferred for detecting the full spectrum of contrast-enhancing lesions of the central nervous system.

Adolescent↗
PubMed1993

Optimization of flip angle for T1 dependent contrast in MRI.

The flip angle which maximizes contrast between materials with different T1 can be calculated from the root of a cubic expression. A simple closed form expression can be used if contrast is defined in a differential sense and results in only slight contrast loss even with large T1 differences.

Algorithms↗
PubMed1993

Magnetic resonance imaging of blood flow with a phase subtraction technique. In vitro and in vivo validation.

RATIONALE AND OBJECTIVES: One promising approach to flow quantification uses the velocity-dependent phase change of moving protons. A velocity-encoding phase subtraction technique was used to measure the velocity and flow rate of fluid flow in a phantom and blood flow in volunteers. METHODS: In a model, the authors measured constant flow velocities from 0.1 to 270.0 cm/second with an accuracy (95% confidence intervals) of +/- 12.5 cm/second. There was a linear relationship between the magnetic resonance imaging (MRI) measurement and the actual value (r2 = .99; P = .0001). RESULTS: Measuring mean pulsatile flow from 125 to 1,900 mL/minute, the accuracy of the MRI pulsatile flow measurements (95% confidence intervals) was +/- 70 mL/minute. There was a linear relationship between the MRI pulsatile flow measurement and the actual value (r2 = .99; P = .0001). In 10 normal volunteers, the authors tested the technique in vivo, quantitating flow rates in the pulmonary artery and the aorta. The average difference between the two measurements was 5%. In vivo carotid flow waveforms obtained with MRI agreed well with the shape of corresponding ultrasound Doppler waveforms. CONCLUSIONS: Velocity-encoding phase subtraction MRI bears potential clinical use for the evaluation of blood flow. Potential applications would be in the determination of arterial blood flow to parenchymal organs, the detection and quantification of intra- and extra-cardiac shunts, and the rapid determination of cardiac output and stroke volume.

Adult↗
PubMed1993

Quantitative differential pulmonary perfusion: MR imaging versus radionuclide lung scanning.

PURPOSE: To compare the results of quantitative analysis of differential pulmonary artery blood flow performed with phase-contrast cine magnetic resonance (MR) images with those of differential radionuclide pulmonary perfusion scanning in preoperative lung transplantation patients. MATERIALS AND METHODS: Forty preoperative lung transplantation patients underwent prospective, quantitative analysis of differential pulmonary artery blood flow performed with MR imaging and radionuclide pulmonary perfusion scanning. MR imaging analysis was performed at 1.5 T with a phase-contrast cine pulse sequence to acquire data perpendicular to each central pulmonary artery. RESULTS: Comparative analysis of differential pulmonary perfusion showed excellent correlation between the two modalities in all patients (P = .0001). MR imaging enabled calculation of the pulmonary artery blood flow to each lung; radionuclide lung scanning enabled only calculation of relative perfusion to each lung. CONCLUSION: MR imaging is as effective as radionuclide lung scanning in assessment of relative, and superior for determination of absolute differential, pulmonary perfusion.

Humans↗
PubMed1993

Fast multiplanar spoiled gradient-recalled imaging of the liver: pulse sequence optimization and comparison with spin-echo MR imaging.

OBJECTIVE: The purpose of this study was to optimize a new rapid-acquisition MR pulse sequence, called fast multiplanar spoiled gradient-recalled (FMPSPGR) imaging, for breath-hold imaging of the liver and to compare unenhanced and contrast-enhanced FMPSPGR with standard spin-echo imaging in detecting liver tumors. MATERIALS AND METHODS: The pulse sequence was optimized at 1.5 T with a healthy volunteer. Various scanning parameters were evaluated, and liver-spleen signal difference/noise measurements were used to estimate lesion contrast-to-noise ratios. We examined 24 patients with hepatic masses using the optimized sequence with spin-echo T1-weighted and T2-weighted imaging as well as unenhanced and gadopentetate dimeglumine-enhanced FMPSPGR imaging. The contrast-to-noise ratio for the hepatic tumors was determined for each sequence. Three radiologists who did not know the biopsy or test results reviewed all images for lesion conspicuity, lesion tissue specificity, and overall image quality. RESULTS: A comparison of unenhanced FMPSPGR images with spin-echo T1-weighted images showed a 40% improvement in mean contrast-to-noise ratio and a 70% improvement in liver signal-to-noise ratio for the FMPSPGR images. A comparison of gadopentetate dimeglumine-enhanced FMPSPGR images with spin-echo T1- and T2-weighted images showed a superior contrast-to-noise ratio for the enhanced FMPSPGR images in 17 (68%) of 25 hepatic lesions, which included all hepatic cysts (n = 3) and all hepatomas (n = 6), and in six of 12 patients with other liver tumors. The results of contrast-to-noise ratio for four patients with hemangiomas were mixed. For the remaining eight lesions, the contrast-to-noise ratio for spin-echo T1- and T2-weighted images predominated in three and five cases, respectively. Contrast-enhanced FMPSPGR images revealed a 40% and 300% increase in contrast-to-noise ratio compared with T2- and T1-weighted images, respectively. All three radiologists preferred the contrast-enhanced FMPSPGR images for overall image quality. For lesion conspicuity and specificity, however, the three radiologists differed, with a preference for the FMPSPGR images in 52%, 80%, and 40% of cases for lesion conspicuity and in 68%, 40%, and 60% of cases for lesion specificity. CONCLUSION: FMPSPGR is a new, ultrafast MR sequence that provides T1-weighted images of the liver during suspended respiration. Contrast-to-noise ratio and liver signal-to-noise ratio are significantly improved over those on conventional spin-echo T1-weighted images. The combination of breath-hold FMPSPGR with gadopentetate dimeglumine is an excellent technique that can be used to rapidly evaluate the liver with superior overall image quality. Contrast-to-noise ratios are generally superior to T2-weighted spin-echo images, making this technique a useful adjunct to conventional spin-echo MR imaging.

Adult↗