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Biomedical subjects

E K Yucel

Publications and source records attributed to E K Yucel.

At least 19 recordsLinked to original sources
PubMed2000

Turbo STIR magnetic resonance imaging as a whole-body screening tool for metastases in patients with breast carcinoma: preliminary clinical experience.

This study was undertaken to assess the utility of whole-body turbo short tau inversion recovery (STIR) magnetic resonance imaging (MRI) to detect metastases to liver, brain, and bone as a single examination in women with breast cancer. Seventeen patients with biopsy-proven breast cancer and suspected metastatic disease attending over a 12-month period referred for both conventional imaging and whole-body MRI were included in the study. Three patients were found to be free of metastases at both conventional and MR imaging. Appendicular or axial skeletal metastases were identified in 11 of 17 patients, with correlation between findings at whole-body MRI and scintigraphy in 15 of the 17 patients. Five patients had evidence of hepatic metastases on whole-body MRI, of which metastases were identified in only three patients at CT despite contrast enhancement. Four patients had brain abnormalities (metastases in three patients, meningioma in one patient) detected on both whole-body and dedicated brain MRI. Preliminary clinical experience suggests that turbo STIR whole-body MRI may represent a convenient and cost-effective method of total body screening for metastases in patients with breast carcinoma.

Adult↗
PubMed1999

Contrast agent-enhanced, free-breathing, three-dimensional coronary magnetic resonance angiography.

For free-breathing, high-resolution, three-dimensional coronary magnetic resonance angiography (MRA), the use of intravascular contrast agents may be helpful for contrast enhancement between coronary blood and myocardium. In six patients, 0.1 mmol/kg of the intravascular contrast agent MS-325/AngioMARK was given intravenously followed by double-oblique, free-breathing, three-dimensional inversion-recovery coronary MRA with real-time navigator gating and motion correction. Contrast-enhanced, three-dimensional coronary MRA images were compared with images obtained with a T2 prepulse (T2Prep) without exogenous contrast. The contrast-enhanced images demonstrated a 69% improvement in the contrast-to-noise ratio (6.6 +/- 1.1 vs. 11.1 +/- 2.5; P < 0.01) compared with the T2Prep approach. By using the intravascular agent, extensive portions (> 80 mm) of the native left and right coronary system could be displayed consistently with sub-millimeter in-plane resolution. The intravascular contrast agent, MS-325/AngioMARK, leads to a considerable enhancement of the blood/muscle contrast for coronary MRA compared with T2Prep techniques. The clinical value of the agent remains to be defined in a larger patient series. J. Magn. Reson. Imaging 1999;10:790-799.

Contrast Media↗
PubMed1999

Voxel sensitivity function description of flow-induced signal loss in MR imaging: implications for black-blood MR angiography with turbo spin-echo sequences.

The conditions in which the image intensity of vessels transporting laminar flow is attenuated in black-blood MR angiography (BB-MRA) with turbo spin-echo (TSE) and conventional spin-echo (CSE) pulse sequences are investigated experimentally with a flow phantom, studied theoretically by means of a Bloch equation-voxel sensitivity function (VSF) formalism, and computer modeled. The experiments studied the effects of: a) flow velocity, b) imaging axes orientation relative to the flow direction, and c) phase encoding order of the TSE train. The formulated Bloch equation-VSF theory describes flow effects in two-dimensional (2D)- and 3D-Fourier transform magnetic resonance imaging. In this theoretical framework, the main attenuation mechanism instrumental to BB-MRA, i.e., transverse magnetization dephasing caused by flow in the presence of the imaging gradients, is described in terms of flow-induced distortions of the individual voxel sensitivity functions. The computer simulations predict that the intraluminal homogeneity and extent of flow-induced image intensity attenuation increase as a function of decreasing vessel diameter, in support of the superior image quality achieved with TSE-based BB-MRA in the brain.

Blood Flow Velocity↗
PubMed1999

Whole-body MR imaging. Practical issues, clinical applications, and future directions.

Whole-body MR imaging is in evolution, and although accepting and recognizing limitations, it is likely that both technique and incurred acquisition times will shorten over the next decade. Although the development of dedicated whole-body MR scanners appears to offer the greatest promise for the future, the development of moving table tops, optimized pulse sequences, and advances in gradient technology now facilitate practical whole-body MR imaging using existing clinical systems.

Adult↗
PubMed1999

Advances in abdominal, aortic, and peripheral contrast-enhanced MR angiography.

This article reviews the basic principles of contrast-enhanced MR angiography, including methods used for sequence optimization and bolus timing, and describes clinical applications of contrast-enhanced MR angiography in the aortic, abdominal, and peripheral arteries. Novel MR angiography imaging techniques also are described, including moving table-top MR angiography, MR fluoroscopy, and time-resolved MR angiography.

Abdomen↗
PubMed1998

Response of normal aorta to endovascular grafting: a serial histopathological study.

OBJECTIVE: To examine the histological changes caused by the presence of the endovascular stented graft in the native aorta. DESIGN AND INTERVENTION: Case series. Twenty Western crossbred adult male sheep underwent endovascular placement of an infrarenal aortic stented graft, using the Bard aortic aneurysm repair device catheter delivery system (Bard Vascular Systems, Dovermill, Mass). Six self-expanding wire hooks at the proximal anchor allow fixation to the aorta. After 1 month (n=6), 3 months (n=6), and 6 months (n=8), the animals underwent repeated angiography and intravascular ultrasonography to study the aorta and the graft. The aorta was explanted en bloc with the left renal artery, pressure perfused with a formalin gluteraldehyde solution, and then underwent histological examination with hematoxylin-eosin, trichrome, and elastic tissue staining. MAIN OUTCOME MEASURES: Description of histological changes at various intervals after endovascular stented graft placement. RESULTS: Significant histological findings include (1) complete incorporation of the grafts into the aortic wall, with a pseudointima of smooth muscle cells and collagen; (2) a foreign-body reaction around the graft; (3) an organized blood clot noted between the graft and the aortic wall, without evidence of recent blood flow through the perigraft space or the lumbar vessels; and (4) focal replacement by collagen of the inner one third to one half of the media at the proximal anchor sites. CONCLUSION: There was good incorporation of the graft without evidence of pressure necrosis, bleeding around the graft, or flow in the occluded lumbar vessels.

Animals↗
PubMed1998

Steady-state and dynamic MR angiography with MS-325: initial experience in humans.

PURPOSE: To evaluate the imaging performance and patient tolerance of a blood-pool contrast agent (MS-325) for magnetic resonance (MR) angiography. MATERIALS AND METHODS: Imaging of peripheral and carotid vessels was performed in seven healthy volunteers in a phase I clinical trial of the gadolinium chelate MS-325. Each volunteer received an intravenous injection of 0.05 mmol/kg MS-325 over 30 seconds. Dynamic (arterial phase) and steady-state (arterial-venous phase) three-dimensional gradient-echo MR angiograms were acquired during, immediately after, and approximately 50 minutes after injection. Images were ranked (1 [poor] to 5 [excellent]) for overall image quality, and signal-to-noise ratio (S/N) and contrast-to-noise ratio (C/N) were measured by using standard techniques. RESULTS: All volunteers tolerated the procedure well. The MS-325-enhanced studies demonstrated intense vascular signal. Mean peripheral arterial C/N was 12.9 +/- 4.8 (standard deviation), 78.8 +/- 29.4, 46.1 +/- 10.9, and 41.9 +/- 14.1 for the two-dimensional (2D) time-of-flight (TOF) and the contrast material-enhanced dynamic, early steady-state, and late steady-state images, respectively. Image quality of steady-state postcontrast images was statistically significantly (P < .02) higher than that of 2D TOF images. Image quality of early and late postcontrast images was similar, but a small (10%) decrease in C/N was noted from early to late images. CONCLUSION: MS-325 provides excellent vascular and selective arterial enhancement during dynamic MR angiography. The long blood residence time also allows acquisition of steady-state images of the arteries and veins with excellent spatial resolution.

Abdomen↗
PubMed1997

A new generation endovascular graft for repair of abdominal aortic aneurysms.

BACKGROUND: Several endovascular grafts are currently being evaluated for repair of abdominal aortic aneurysms (AAA). The goals of our study were twofold. First was to develop a new endovascular graft with several advantages over previous devices: (1) smaller size (16 fr), (2) recapturability (the device can be partially deployed and then recaptured and moved to a new location or entirely removed if needed), and (3) accuracy and ease of placement. Our second goal was to develop an animal model in which a full-scale prototype of the device could be tested. METHODS: Our final endovascular graft prototype was developed after extensive in-vitro testing, and trials of earlier prototypes in dog, pig, and female sheep models. Uncastrated male sheep, 75 to 100 kg, were chosen as the animal model in which to test the device. These animals had infrarenal aortas that were comparable to that of small humans, with diameters of 12 to 15 mm. Two models were used: (1) native infrarenal aorta, and (2) artificial infrarenal aneurysm. Pre-implant and postimplant angiography and intravascular ultrasound were used to evaluate graft placement, and were repeated prior to euthanasia and necropsy. RESULTS: The final prototype was implanted in 22 animals. Sixteen animals had the device placed in their native infrarenal aorta. Three animals were sacrificed immediately after implantation, and 6 more were euthanized after 2 weeks (n = 2), 6 weeks (n = 2), and 3 to 4 months (n = 2). In 7 animals the device is still in place. All procedures were successful. Pathology confirmed complete exclusion of the aorta and thrombosis of all lumbar branches covered by the graft. There was no evidence of graft malposition, migration, or perigraft leak, and no evidence of significant vessel injury on histology. Six animals had artificial aneurysms surgically created and then repaired with the device. A technical error resulted in a failure in 1 case; the remaining aneurysms were all successfully excluded. CONCLUSIONS: We report the development of a new endovascular prosthesis for the repair of AAA. Newer design features provide for smaller delivery size (16 fr), facilitate accurate placement, and provide the option when the device is partially deployed to recapture and reposition the device if necessary. In addition, we have developed an animal model in which this device, and future endovascular aortic devices, can be tested.

Animals↗
PubMed1997

MR imaging of soft tissues adjacent to orthopaedic hardware: techniques to minimize susceptibility artefact.

This article demonstrates and compares imaging of orthopaedic hardware (fixation plates, screws, Kischner wire and prostheses) using gradient-echo, spin-echo and fast spin-echo sequences. It describes simple techniques which minimize susceptibility artefact induced by these components at magnetic resonance (MR) imaging, allowing visualization of adjacent soft tissues. The article emphasizes the importance of selecting the appropriate imaging plane in order to avoid hardware distortion of slice select gradients, emphasizes the importance of selecting frequency encoding gradient axes in order to orientate the long axis of the artefact away from the tissue of interest and, finally, compares the marked susceptibility artefact observed adjacent to hardware using gradient-echo with the artefact reduction achieved by using fast spin-echo sequences.

Artifacts↗
PubMed1997

T2-weighted MR imaging of the liver: optimization of hybrid-RARE sequences.

The objectives of this study were to optimize T2-weighted hybrid-RARE pulse sequences for clinical MR imaging of the liver, and to compare them to the conventional spin-echo (CSE) sequence. Specifically, the ranges of the echo train length (ETL) and the effective echo time (TEeff) were investigated to optimize image quality and liver-spleen contrast, in healthy volunteers. A total of thirteen volunteers were scanned at 1.5 Tesla with an extensive array of hybrid-RARE scans. The images were analyzed quantitatively with respect to CNR (contrast-to-noise ratio of spleen vs. liver), SNR (signal to noise ratio of the spleen), SIR (signal intensity ratio of liver and spleen) and CDR (contrast difference ratio between the spleen and liver). The images were also analyzed qualitatively with respect to image sharpness, vascular artifacts, ghosting, chemical shift, and truncations. Results of quantitative analysis indicated that CDR and SIR of hybrid-RARE at higher ETL (> 13) were consistently better than both the reference CSE and the lower ETL sequences (p < 0.05) at all TEeff. SNR was slightly inferior for all hybrid-RARE sequences than for the CSE sequence. Image quality for hybrid-RARE sequences with ETL > 13 proved to be consistently better than that for the CSE (TE = 90 ms) with respect to imaging sharpness, vascular artifacts and ghosting artifacts (p < 0.05). In conclusion, the optimized hybrid-RARE sequences with ETL greater than or equal to 13 are capable of producing sharp and relatively artifact free images with the advantage of a much greater acquisition time efficiency.

Adult↗