Biomedical subjects

E K Yucel

Publications and source records attributed to E K Yucel.

78 records · Page 5Linked to original sources

PubMedDate not supplied

Single-shot magnetic resonance imaging: applications to angiography.

Recently developed technologies that allow the collection of magnetic resonance imaging (MRI) in as little as 26 msec have been explored in their application to angiography. Advantages are demonstrated in scan time reduction, insensitivity to patient motion (especially in abdominal applications), flow quantification, and temporal resolution. We demonstrate that because such single-shot techniques are inherently resistant to flow dephasing during acquisition that allow for sustained high signal intensities to be achieved when images must be combined through the cardiac cycle. Such high temporal resolution scans may be utilized for the collection of time-resolved angiograms. With these techniques we demonstrate the collection of complete MR angiograms in the course of reasonable 10-25 sec breath holds. The relative simplicity of the technique, coupled with its overall short acquisition time, allows us to incorporate angiography into other imaging protocols without adding significant time burdens. Results to date are promising for further improvements in spatial resolution, without extension of scan time.

Algorithms↗

PubMedDate not supplied

Iliac artery aneurysms. Radiographic evaluation.

We present seventeen cases of iliac artery aneurysm employing a variety of different imaging modalities (ultrasound, computed tomography, arteriography, magnetic resonance imaging). The utility of each of these techniques in the patient with iliac artery aneurysm is described.

Adult↗

PubMedDate not supplied

MR angiography in the preoperative evaluation of abdominal aortic aneurysms: a preliminary study.

PURPOSE: The ability of magnetic resonance (MR) angiography to depict visceral and renal vessels was evaluated in patients with abdominal aortic aneurysms (AAAs). PATIENTS AND METHODS: MR sequences (sagittal T1-weighted, two-dimensional coronal, and three-dimensional axial time-of-flight) were compared in a prospective blinded fashion with conventional angiograms obtained preoperatively in 23 patients with AAAs. Results were correlated with surgical findings when available. RESULTS: Operative aortic clamp site was correctly predicted with conventional angiography in 95% of patients and with MR angiography in 86% (P > .1). Aneurysm neck measurements obtained with the two modalities were within 1 cm in 91% of cases. With conventional angiography as the standard of reference, 96% of all renal arteries were identified on MR angiograms but 36% of accessory arteries were missed. MR angiography enabled identification of patients who had at least one renal artery stenosis greater than 50% with a sensitivity of 100% and specificity of 89%. For identifying individual renal artery, celiac artery, and superior mesenteric artery stenoses of similar severity, the sensitivity and specificity were 67% and in excess of 96%, respectively. The celiac artery could not be evaluated in one case. CONCLUSION: The results of this small study suggest that the role of MR angiography in the preoperative evaluation of AAA warrants further investigation.

Aged↗

PubMedDate not supplied

Two- and three-dimensional phase contrast MR angiography of the abdomen.

Protocols for two- and three-dimensional phase contrast magnetic resonance angiography of the major vessels in the abdomen were developed and demonstrated in healthy volunteers. Phase contrast imaging provides excellent suppression of stationary tissue signal and can be used to quantify the speed and direction of flow in a given vessel. The two-dimensional protocols provide rapid breath-held images, which proved useful for anatomical localization. The three-dimensional studies required longer acquisition times but provided superior image quality. Artifacts from bowel and respiratory motion were not significant with either protocol. Vasculature detected includes the renal, splenic, hepatic, and mesenteric systems as well as the aorta and inferior vena cava.

Abdomen↗

PubMedDate not supplied

Reduction of artifacts from breathing and peristalsis in phase-contrast MRA of the chest and abdomen.

Strategies for the acquisition of temporally resolved phase-contrast angiography are described and demonstrated. Projections are acquired through the entire thickness of the subject permitting excitation geometries to be independent of image orientation. Minimal delays are used between the acquisition of oppositely flow-encoded data resulting in fewer artifacts from movement of nominally stationary tissue. A protocol that suppresses artifacts from both peristalsis and breathing is presented for the aortic arch and iliac arteries.

Abdomen↗

PubMedDate not supplied

Signal characteristics of focal liver lesions on double echo T2-weighted conventional spin echo MRI: observer performance versus quantitative measurements of T2 relaxation times.

PURPOSE: The purpose of this work was to evaluate the ability of expert readers to differentiate benign from malignant liver lesions based on visual assessment of lesion signal intensity on double echo T2-weighted conventional spin echo (CSE) MR images and to compare reader performance with quantitative measurements of T2 relaxation times. METHOD: Sixty-seven MR examinations demonstrating 85 liver lesions (37 hemangiomas, 32 malignancies, 15 cysts, and 1 focal nodular hyperplasia) on double echo T2-weighted CSE sequences (TR 3,600 ms/TE 50, 160 ms) were qualitatively reviewed by three independent readers. T2 relaxation times were calculated for each lesion. Receiver operating characteristic (ROC) analyses of expert readers were compared with calculated T2 relaxation times. RESULTS: T2 values performed significantly better than subjective reader analysis for liver lesion characterization (area under ROC = 0.93 vs. 0.81, 0.78, and 0.75; p < 0.0001). With use of a T2 threshold of 125 ms, the sensitivity of T2 values for malignant lesions was 100%, specificity 71%, and accuracy 84%. By comparison, the sensitivity of the three readers for malignant lesions was 76-83%, with a specificity of 61-72% and an overall accuracy of 71-80%. CONCLUSION: Despite expert reader analyses, subjective evaluations of liver lesion signal characteristics are prone to inaccuracy and lack certainty and consistency when intermediate TEs (50/160 ms) are used. Quantitative measurements of T2 relaxation times should be performed to accurately and confidently differentiate benign from malignant liver lesions. Use of a higher T2 threshold than previously recommended is required to avoid misclassification of malignancies.

Adult↗