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Biomedical subjects

P Wielopolski

Publications and source records attributed to P Wielopolski.

9 recordsLinked to original sources
PubMed1999

[Comparison of conventional and high resolution 2D RARE MRCP in diagnosis of pancreaticobiliary diseases].

PURPOSE: Evaluation of high-resolution 2D-RARE MRCP in the diagnosis of pancreaticobiliary diseases. MATERIALS AND METHODS: 23 patients with various pancreaticobiliary diseases were evaluated using conventional and high-resolution 2D-RARE sequences. RESULTS: High-resolution RARE MRCP allowed for improved delineation of biliary and pancreatic ducts at the expense of reduced signal-to-noise ratio. Pathological findings were significantly (p < 0.001) better demonstrated with high resolution RARE MRCP (score 1.65 +/- 0.54) as compared to the conventional RARE sequence (score 2.58 +/- 0.62). CONCLUSIONS: High-resolution 2D-RARE-MRCP improves the delineation of biliary and pancreatic ducts. This sequence should replace the conventional 2D-RARE sequence.

Adult↗
PubMed1996

Noninvasive perfusion imaging of human brain tumors with EPISTAR.

A total of 17 patients with histologically proven diagnoses of low-grade astrocytoma (n = 4), high-grade astrocytoma (n = 8), lymphoma (n = 3), and meningioma (n = 2) were examined by using EPISTAR MR imaging. Meningiomas had the highest EPISTAR tumor/white matter contrast and low-grade astrocytomas and lymphomas the lowest. High-grade astrocytomas demonstrated elevated EPISTAR signal with marked regional heterogeneity. There was agreement between tumor vascularity by SPECT and EPISTAR in the five cases where both were done. Our results show that tumor vascularity can be assessed qualitatively by using EPISTAR without the need for contrast medium injection.

Adult↗
PubMed1996

[Magnetic resonance angiography of the carotid artery: effect of short and ultra-short echo times].

PURPOSE: To evaluate the influence of short and ultrashort echo times (TE) on the magnetic resonance (MR) signal in the carotid sinus and in carotid artery stenoses. MATERIAL AND METHODS: High resolution gradient-echo sequences without and with flow compensation using TE's ranging from 1.5 to 8.0 ms were compared on phantoms, eight healthy volunteers, and 10 patients with moderate and severe carotid artery stenoses. RESULTS: MR sequences with shortest TE's provided the best visualisation of stenotic regions in the carotid sinus and demonstrated a substantial reduction of signal loss due to spin dephasing in both phantom and patient studies. This was made possible using an improved gradient system with higher gradient strengths and shorter rise times with lower acquisition bandwidths and better signal-to-noise ratio. CONCLUSION: MR sequences with short and ultrashort TE's enable a better definition of the stenotic region and therefore guide adequate therapeutic decisions.

Adult↗
PubMed1996

Magnetic resonance coronary angiography in heart transplant recipients.

BACKGROUND: Annual coronary angiography is routinely performed to evaluate cardiac allografts. Recently, magnetic resonance coronary angiography has been used to imagine native coronary arteries, but its use in transplant recipients, with rapid heart rates, metallic sternal sutures, and altered cardiac orientation, has not been described. Our goal was to describe the feasibility of noninvasive magnetic resonance coronary angiography in cardiac allograft recipients, detect flow-limiting focal stenoses, and quantify the altered coronary artery orientation. METHODS AND RESULTS: We performed magnetic resonance coronary angiography is 18 adult heart transplant recipients (15 men and 3 women) with use of a breath-hold ECG-gated segmented k-space technique. Multiple transverse and oblique images were obtained in each subject. A control population of 16 adult patients without transplant and without angiographic evidence of coronary disease provided a reference for the coronary artery length visualized by magnetic resonance coronary angiography. This technique identified the left main coronary artery in 15 of 15 transplant recipients with normal coronary anatomy. Magnetic resonance coronary angiography demonstrated a +25-degree anterior (clockwise) right coronary artery ostial rotation in transplant recipients (p = 0.0001 versus control group) with corresponding realignment of the left main ostium. By magnetic resonance coronary angiography, the mean contiguous length of coronary artery visualized in the transplant recipients was similar to that in the control subjects for all major vessels (p = not significant). Five transplant recipients had nine discrete stenoses (50% or greater luminal diameter) identified by contrast angiography, of which seven stenoses were identified as signal voids by magnetic resonance coronary angiography. coronary stenoses not seen by this technique were located in the distal one third of the artery. CONCLUSIONS: These data confirm and for the first time quantify the previously observed anterior rotation of the coronary ostia, which may be used to guide coronary engagement for subsequent interventions. In addition, these data demonstrate the potential of magnetic resonance coronary angiography to image noninvasively the coronary arteries and identify focal stenoses in cardiac allograft recipients.

Adolescent↗
PubMed1995

Acute human stroke studied by whole brain echo planar diffusion-weighted magnetic resonance imaging.

Our purpose was to use whole brain echo planar magnetic resonance imaging (MRI) to identify and characterize diffusion abnormalities in acute cerebral ischemia. We studied 40 patients as early as 3 hours after onset of signs and symptoms of cerebral ischemia. Diffusion-weighted imaging (DWI) of the entire brain could be completed in 3 seconds or, using seven different diffusion sensitivities (maximum b = 1,271 sec/mm2), in 48 seconds. Measurements and synthetic maps were made of apparent diffusion coefficients (ADC), a physiological parameter that characterizes the self-diffusion of water in tissue. Early ischemic lesions were identified with DWI as hyperintense regions of decreased ADC in all patients who subsequently developed infarction, before changes were evident on conventional MRI in cases studied earlier than 6 hours after onset of ischemic symptoms. Lesions as small as 4 mm in diameter were identified. The extent of lesions within white matter was best defined by controlling for the anisotropic effect of axonal orientation. The mean ADC (+/- SD) for control regions in the 36 patients was 9.15 (+/- 2.91) x 10(-4) mm2/sec. Mean ADC of ischemic regions was 56% of control values at 6 hours or less and stayed significantly reduced for 3 to 4 days after onset of ischemia. The relative ADC increased progressively over time to be pseudonormalized at 5 to 10 days and elevated in the chronic state, making the distinction of acute lesions adjacent to chronic infarcts readily apparent. DWI with echo planar imaging measures a unique physiological parameter that is sensitive to ischemic changes before conventional MRI. Its potential role in the quantitative study of human stroke pathophysiology and therapeutics is the subject of further investigation.

Adult↗
PubMed1994

Signal targeting with alternating radiofrequency (STAR) sequences: application to MR angiography.

We describe a time of flight subtraction method for cine MR angiography that provides nearly perfect suppression of background signal intensity with excellent flow contrast. The method consists of a preparation phase, during which the longitudinal magnetization of the target tissue is inverted on alternate acquisitions and the background tissue is presaturated, followed by a readout phase using a cine segmented turboFLASH sequence with a shared echo modification to improve temporal resolution. With appropriate alternation of the phases of the radiofrequency excitation pulses, there is cancellation of the background signal intensity but flow signal is optimized. By using a thick section (up to 25 mm), substantial portions of the vascular territory are encompassed in a single plane. This permits rapid, dynamic assessment of flow patterns in areas such as the circle of Willis, carotid bifurcation, or renal arteries. Applications of the method for bright and dark blood cine MR angiography are demonstrated.

Aorta, Abdominal↗
PubMed1991

The stability of proton T2 effects of oxygen-17 water in experimental cerebral ischemia.

The gerbil model of unilateral cerebral ischemia has been used to test the temporal and spatial stability of the MRI T2 effects of oxygen-17 water. Following unilateral carotid ligation, symptomatic animals were given a single large intraperitoneal injection of H2(17)O and the distribution and stability of the brain T2 effects were followed with a spin-echo sequence. In contrast to the ischemic areas, the perfused tissue shows a marked and prolonged loss in intensity with little evidence of diffusion of the T2 effect of 17O into the ischemic tissue.

Animals↗
PubMedDate not supplied

Magnetic resonance imaging of the brain with gadopentetate dimeglumine-DTPA: comparison of T1-weighted spin-echo and 3D gradient-echo sequences.

Short TR, short TE, high resolution, 3D gradient-recalled echo (GRE) imaging was evaluated for lesion detection in the brain. High resolution 3D GRE data acquisition was used to reduce partial volume effects and flow artifacts, to better visualize smaller structures, to minimize signal losses caused by field inhomogeneities, and to allow better image reformatting. Spin-echo (SE) and 3D GRE approaches were compared for lesion detection after the administration of an MR contrast agent, gadopentetate dimeglumine. Preliminary clinical studies demonstrated that the signal-to-noise ratio (SNR) in each slice of the GRE scan was worse than that of the SE scan because of the much thicker slices acquired with the SE technique. However, by averaging two adjacent 3D slices, the SNR of the two methods was essentially equivalent. In the averaged GRE slices, large lesions were seen just as well as in the SE images. More importantly, small lesions were better visualized in the thin 3D GRE images than in the thick SE images for the lesions studied in this work and the protocols used. These observations were confirmed by theoretical simulations.

Adolescent↗