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Biomedical subjects

A N Shetty

Publications and source records attributed to A N Shetty.

At least 19 recordsLinked to original sources
PubMed2000

Contrast-enhanced breath-hold three-dimensional magnetic resonance angiography in the evaluation of renal arteries: optimization of technique and pitfalls.

The authors describe the optimization of a contrast-enhanced, breath-held, three-dimensional magnetic resonance angiography (CE-BH-3DMRA) technique in the assessment of the renal arteries and compare its utility with conventional x-ray angiography (XRA). Signal optimization using specific pulse sequence parameters was based on the patient's circulatory conditions, injection rate, and pulse sequence timing. Fifty-one patients (27 M, 24 F; mean age 69.7 years) were evaluated with CE-BH-3DMRA and XRA. All patients had an MR angiogram 3 months either before or after XRA. A test bolus study was performed for accurate assessment of transit time in each patient. A total of 51 patients (115 vessels) were studied in which the sensitivity and specificity for all renal artery stenoses including the proximal and mid-renal arterial segments were 96% and 92%, respectively. In-stent stenosis could only be diagnosed by quantifying flow beyond the stent using an additional triggered phase contrast cine pulse sequence. A total of 11 accessory renal arteries were correctly identified. In addition, fibromuscular dysplasia in two patients and stents in three patients were correctly identified on MRA. J. Magn. Reson. Imaging 2000;12:912-923.

Adult↗
PubMed1999

Dynamic contrast-enhanced 3D breath hold MRA using a multiple variable orientation slab acquisition.

With the conventional 3D MR angiographic sequences, it is difficult to prescribe multiple phases in different orientations, though multiple phases may be prescribed in the same orientation as the initial scan. Magnetic resonance angiography (MRA) was performed in which three slabs were prescribed in different orientations and were acquired in a sequential measurement. A fixed delay of 8 s between the slabs was used to prepare patients to hold their breath for subsequent measurements. All subjects tolerated the entire breath hold examination. The results were easily reproducible and yielded high-resolution 3-dimensional images in various planes.

Aortic Diseases↗
PubMed1999

Breath-hold 3D MR angiography of the renal vasculature using a contrast-enhanced multiecho gradient-echo technique.

OBJECTIVE: Significant evolution of contrast-enhanced MR angiography for evaluating vascular diseases in the abdomen has occurred during the past several years. The state-of-the-art gradient-echo imaging technique employs a short echo time (TE) and a short repetition time (TR) for rapid vascular imaging with contrast-enhanced MR angiography. However, because of the short TR (< or = 3-8 msec), the background stationary tissue becomes saturated, with resultant poor contrast resolution of visceral organs. The authors present a new approach to vascular imaging using a multiecho gradient-echo technique with a TR sufficiently long (41 msec) to image the renal vasculature and parenchyma without background tissue suppression. METHODS: Twenty-four partitions (3D slab thickness = 72 mm) with an in-plane resolution of 224 x 256 were obtained in 21 seconds. Three measurements were performed with an interscan delay of 8 seconds. In the pulse sequence, the partition loop is defined as the innermost loop, in which Kz views are acquired centrically for a fixed Ky, followed by Ky views in a conventional linear or sequential order. The partition encodings are segmented to permit multiple encodings in which two TR loops were used to span a total of 24 echoes with 12 along the positive and 12 along the negative direction in k space. A large bandwidth of 650 Hz/pixel was used to keep the echo train length short, with an echo spacing of 1.86 msec. A frequency-selective fat saturation pulse was placed before slab-selective excitation. The other parameters in the pulse sequence were TR/TE/flip = 41/2.2/45; the field of view was 360 to 390 mm. Maximum intensity projections of each 3D contrast-enhanced measurement were performed. The vascular-to-background contrast, bowel-related magnetic susceptibility artifact, and background stationary signals were subjectively graded. The authors examined the utility of this technique in 16 randomly selected patients (3 normal, 13 abnormal) with varied renal vasculature and parenchymal abnormalities. Results were confirmed with conventional x-ray angiography, surgery, or clinical follow-up. RESULTS: Vascular-to-background contrast was graded as very good (grade III/III) in all cases. The bowel-related magnetic susceptibility artifacts were not considered significant. Background visceral organ soft tissue contrast was not suppressed and was graded as good (grade III/III) in all cases. Eight hemodynamically significant (> 50% diameter) stenoses in seven patients were accurately assessed (one with fibromuscular dysplasia). Three patients with renal masses (two with renal cell carcinoma and one with renal lymphoma) were accurately assessed for arterial anatomy and venous extension. Other renal venous abnormalities seen were retroaortic renal vein (n = 1), chronic occlusion (n = 1), and accessories (total of five) (n = 1). CONCLUSIONS: Rapid breath-hold contrast-enhanced MR angiography of the renal vasculature with a multiecho gradient-echo using a long TR depicted the renal vasculature with high vessel-to-background contrast without significant bowel-related susceptibility artifact and without background visceral organ tissue signal suppression, resulting in high background soft tissue contrast resolution.

Artifacts↗
PubMed1997

Mesenteric circulation: three-dimensional MR angiography with a gadolinium-enhanced multiecho gradient-echo technique.

To evaluate the mesenteric circulation with magnetic resonance (MR) angiography, the authors examined 16 individuals (12 patients, four volunteers) with a gadolinium-enhanced, breath-hold, fat-saturated, multiecho, three-dimensional, gradient-echo sequence. Twenty examinations were performed. Grades of 3 or 4 (on a five-point scale [4 = best seen, 0 = not seen]) were applicable to 17 (85%) of 20 MR angiograms obtained in superior mesenteric artery trunks, 15 (75%) in celiac arteries, five (25%) in inferior mesenteric arteries; 15 (75%) of first-order branching, 12 (60%) of second-order branching, and 10 (50%) of third-order branching; 17 (85%) in superior mesenteric veins; and 17 (85%) in portal veins. MR angiography with this technique depicted the mesenteric arterial and venous circulation and the portal vein with excellent resolution in a short time.

Adult↗
PubMed1997

Contrast-enhanced breath-hold MR angiography for evaluating patency of coronary artery bypass grafts.

OBJECTIVE: The purpose of this study was to evaluate the ability of contrast-enhanced breath-hold MR angiography to reveal patency of coronary artery bypass grafts (CABGs). SUBJECTS AND METHODS: We evaluated 45 grafts (29 saphenous vein bypass grafts, 12 left internal mammary artery grafts, and four right internal mammary artery grafts) for occlusion or patency. Fifteen patients who had undergone CABG surgery underwent three-dimensional breath-hold ECG-triggered contrast-enhanced MR angiography at 1.5-T and conventional coronary angiography imaging within 24 hr of each other. MR angiograms were evaluated independently by two radiologists. Agreement between MR angiography and coronary angiography (the reference standard) was measured using Cohen's kappa statistic. RESULTS: One saphenous vein bypass graft was revealed as occluded by coronary angiography but was shown as patent by MR angiography and was excluded from statistical analysis. MR angiography was in agreement with coronary angiography in 42 of 44 grafts (kappa = 90: p < .001; sensitivity, 93%; specificity, 97%). CONCLUSION: Contrast-enhanced breath-hold MR angiography is a promising, rapid, and useful diagnostic technique for detecting graft patency in patients who have undergone CABG surgery.

Adult↗
PubMed1997

MR cholangiopancreatography (MRCP).

Magnetic resonance cholangiopancreatography (MRCP) is an evolving new technique for noninvasive imaging of diseases of the biliary tree and pancreatic duct. The advantage of this method is that one can obtain maximum intensity projection (MIP) images of the pancreatico-biliary system similar to those obtained with endoscopic retrograde cholangiopancreatography (ERCP) without the need of administration of intravenous or oral contrast. Heavily T2-weighted sequences are used that render the bile and the intraductal pancreatic fluid bright against a dark background.

Bile Ducts↗
PubMed1988

Suppression of radiofrequency interference in cardiac gated MRI: a simple design.

A simple design is proposed to suppress the noise pickup in the ECG leads from RF and gradient pulses during NMR imaging. The ECG signal is passed through a low-pass filter and a common-mode-rejection amplifier to reduce erroneous signal generated by the electrical ground loops. The output is gated through a CMOS switch to blank the preamplifier from the NMR during data acquisition.

Electrocardiography↗
PubMed1980

Pseudocysts of the pancreas: an overview.

Of 243 patients with pancreatitis, 4.5% had pseudocyst of the pancreas (11 cases), 90% presented with abdominal pain, 81% had abnormal GI series, and 90% had abnormal urinary amylase. Abdominal sonography was found to be a very useful diagnostic tool.

Adult↗
PubMedDate not supplied

MR imaging of myositis ossificans: variable patterns at different stages.

Five patients with a palpable mass at presentation underwent magnetic resonance (MR) imaging. The final diagnosis was myositis ossificans (MO). MR imaging features, particularly after injection of gadopentetate dimeglumine, mimicked those of an inflammatory mass or neoplasm. The lesions were excised in three patients, and the images were correlated with histologic findings. Three different appearances were noted on MR images, corresponding to the stages of maturation of MO. Two cases involved early-stage lesions, and T1-weighted MR images showed a mass with homogeneous intermediate signal intensity. Both lesions showed rim enhancement after contrast agent injection and high signal intensity on T2-weighted images. Pathologic specimens demonstrated stroma with masses of spindle cells in which osteoid production was interspersed. The enhanced rim of the lesion mimicked the expected MR appearance of an abscess or necrotic tumor. Areas of enhancement in adjacent muscle were also seen on postcontrast T1-weighted images. Intermediate-stage MO was present in one case; there was evidence of a thin rim of calcification on plain radiographs and fatty changes in the lesion on T1-weighted images, corresponding with histologic findings. One case of a mature lesion showed a considerable degree of peripheral calcification both on MR images and at histology. MR imaging is nonspecific in the diagnosis of early-stage MO.

Abscess↗
PubMedDate not supplied

Giant cell tumor of the tendon sheath in the ankle: MRI with pathologic correlation.

We report a case of Giant cell tumor of the tendon sheath involving the ankle, wherein spin-echo (T1- and T2-weighted), gradient-echo, and dynamic contrast-enhanced sequences were performed, and the tumor was noted to be very vascular. To the best of our knowledge, the use of gradient-echo sequences and the pattern of enhancement by time-intensity curves has not been reported earlier.

Adult↗
PubMedDate not supplied

Hypogenetic lung syndrome: functional and anatomic evaluation with magnetic resonance imaging and magnetic resonance angiography.

A case of hypogenetic lung syndrome is described in which anatomic and functional information was obtained with use of ECG-triggered turbo (fast) spin-echo, cine, velocity-encoded cine, and contrast-enhanced magnetic resonance angiography (MRA) sequences. To the best of our knowledge, a complete functional and anatomic study of hypogenetic lung syndrome with MRI has not been previously reported.

Female↗
PubMedDate not supplied

Gradient-echo perfusion imaging of musculoskeletal abnormalities with contrast-enhanced two-dimensional fat-saturation FLASH.

The objective of this study was to evaluate the utility of MR perfusion imaging of various musculoskeletal lesions with a contrast-enhanced two-dimensional fat saturation fast low angle shot (FLASH) sequence and to assess the potential of this technique for distinguishing malignant from benign conditions. Thirty-six musculoskeletal lesions were studied at 1.5 T. The signal intensity of the lesions, adjacent artery, muscle, bone marrow, and fat were plotted against time. The time to peak enhancement, time to maximum signal intensity, percent enhancement, rate of peak enhancement, and rate of enhancement parameters were calculated. Because of a significant overlap between malignant and benign conditions, accuracy rates were lower than reported previously. The best parameter based on these values was the rate of peak enhancement (sensitivity, 84.6%; specificity, 65.2-66.6%; positive predictive value, 57.8-68.7%). Fat saturation gradient-echo MR perfusion imaging allows for a rapid assessment of the vascularity of musculoskeletal pathology; however, a significant overlap persists between malignant neoplasms and several benign conditions.

Adipose Tissue↗
PubMedDate not supplied

Contrast-enhanced 3D MRA with centric ordering in k space: a preliminary clinical experience in imaging the abdominal aorta and renal and peripheral arterial vasculature.

The objective of this study was to determine the clinical utility of a contrast-enhanced, centric reordered, three-dimensional (3D) MR angiography (MRA) pulse sequence in imaging the abdominal aorta and renal and peripheral lower extremity arteries. Twenty-eight MRA studies were performed on 23 patients and four volunteers at 1.5 T using a 3D contrast-enhanced, centric reordered pulse sequence. In 20 patients, the abdominal aorta and renal arteries were imaged, and in seven patients, the lower extremity arteries were imaged. In 19 patients, a total of 51 renal vessels were evaluated (33 renal arteries using .1 mmol/kg of gadopentetate dimeglumine and 18 renal arteries using .2 mmol/kg of gadoteridol). A total of 70 peripheral arterial segments were assessed using .2 mmol/kg of gadoteridol. Correlation with conventional angiography was made for the following 14 cases: renal artery stenosis (four cases), abdominal aortic stenosis (one case), arteriovenous fistula in a transplant kidney (one case), renal arteriovenous malformation (one case), common iliac artery aneurysms (one case), and peripheral lower extremity (six cases). Of the 70 peripheral arterial segments evaluated, in 35, there was correlation with x-ray angiography. The mean percent of aortic signal enhancement was significantly higher in the .2 mmol/kg dose group (370.8 +/- 190.3) than in the .1 mmol/kg dose group (184.5 +/- 128.9) (P = .02). However, there was no apparent difference between the two doses for visualization of the renal and accessory renal arteries. There was concordance between the contrast-enhanced 3D MRA studies and conventional angiography in all cases of renal artery and peripheral arterial stenoses and occlusions, including visualization of reconstituted peripheral arterial segments. There was no evidence of spin dephasing effects at sites of stenoses on the 3D contrast-enhanced MRA studies. Contrast-enhanced, centric reordered, 3D MRA can rapidly image the abdominal aorta and renal and accessory renal arteries, as well as peripheral lower extremity arteries, with high resolution. Accurate depiction of the vascular lumen at sites of stenosis is made because of the lack of spin dephasing effects, even with hemodynamically significant stenoses. Additional larger clinical trials are required with this promising technique.

Adult↗
PubMedDate not supplied

Paravertebral muscle metastases as imaged by magnetic resonance venography: a brief report.

Paraspinal muscle metastasis as initially suggested by an electromyographic pattern of isolated posterior primary ramus denervation and subsequently confirmed by magnetic resonance imaging has been reported. However, despite widespread systemic tumor dissemination, metastases to other skeletal muscle occurs infrequently. Uniquely, the paraspinal muscles are drained by the paravertebral plexus of veins. Valveless and at very low pressures, they communicate directly by collaterals with the portal system. Valsalva maneuvers with sudden increases of pressure within the intra-abdominal and intrathoracic cavities can force venous blood from the systemic circulation into the paravertebral plexus of veins. These same venous surges potentially carry tumor emboli to the vertebrae and/or from the vertebral medulla to the adjacent paravertebral muscle by the venous communicators. The inherent increased vascularity of metastatic tumor relative to the surrounding paraspinal muscle as demonstrated by magnetic venous angiography for the first time now permits earlier confirmation and biopsy of the electromyographic-suspected metastatic lesion. In this reported instance of a magnetic resonance imaging-recognized primary lung metastasis confirmed by magnetic resonance venography, there is the future promise of identifying earlier and smaller lesions by this technique.

Aged↗
PubMedDate not supplied

3D breath-hold contrast-enhanced MRA: a preliminary experience in aorta and iliac vascular disease.

PURPOSE: Our goal was to describe a 3D breath-hold (3D BH) contrast-enhanced MRA technique and apply the technique to patients with known or suspected aortic and iliac artery disease. METHOD: A fat-suppressed 3D GRE pulse sequence was designed with a total of 16 partition encodings. This took < 24 s for data acquisition in the abdomen and pelvis and was easily achieved during a single breath-hold. The technique was applied to 26 patients who presented with either known or suspected abdominal aortic or iliac vascular diseases. For comparison, in 19 patients a 2D TOF MRA pulse sequence with a traveling saturation band was used. Angiographic correlation was made in 18 studies. RESULTS: The 3D BH MRA was easily applicable in the evaluation of vascular anatomy and pathology. In three cases, it was superior to 2D TOF and conventional angiography for visualizing clot within the wall of an aneurysm in the abdominal aorta. In 20 cases, both MRA techniques overestimated the degree of stenosis in the lower peripheral vessels; however, this was more pronounced on 2D TOF. In five cases, the aneurysm wall was clearly defined by 3D BH MRA, whereas there was considerable signal loss in 2D TOF due to complex flow. With 3D BH MRA, the entire vessel territory both in abdominal aorta and in iliac vessels was visualized in all cases without signal falloff in the FOV. Breath-holding provided static images of the vessels that were free of blurring due to respiratory motion. CONCLUSION: Preliminary experience suggests that 3D BH with its distinct advantage of speed may serve as a useful screening tool for patients who cannot have conventional angiography or tolerate a lengthy MR examination of the abdominal aorta and iliac arteries.

Adult↗