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Biomedical subjects

D G Mitchell

Publications and source records attributed to D G Mitchell.

At least 163 records · Page 9Linked to original sources
PubMed1989

Variable-flip-angle spin-echo MR imaging of the pelvis: more versatile T2-weighted images.

Dependence on T1 contrast can be reduced by changing the excitation flip angle. The authors compared T2-weighted spin-echo images (with 30 degrees and 90 degrees flip angles) of the male and female pelvis in 22 individuals. In six women imaged with a 1,000/80 sequence (repetition time msec/echo time msec), signal difference-to-noise ratios (SD/Ns) were higher with a 30 degree flip angle than with a 90 degree angle for urine/fat (mean, 15.2 vs -6.2; P less than .05) and endometrium/myometrium (13.8 vs 9.0, P less than .05). In eight additional examinations, a 1,000/80 sequence with a 30 degree flip angle and two signal averages had less motion artifact (1.2 vs 2.7, P less than .01) than a 2,000/80 sequence with a 90 degree angle and one signal average (4.5 minutes each); SD/Ns were similar. In a third series of experiments, contiguous sections without cross talk, obtained by interleaving two 1,000/100, 30 degrees-flip-angle acquisitions, had better contrast than contiguous sections obtained at 2,400/100 with a 90 degree flip angle (10 minutes each), with SD/Ns of urine/fat of 28.5 versus 16.1 (P less than .01) and SD/Ns of endometrium/myometrium of 15.5 versus 7.8 (P less than .05). Reducing the flip angle can improve examination time, contrast, or motion artifact suppression or eliminate cross talk in T2-weighted spin-echo MR imaging of the pelvis.

Female↗
PubMed1989

Circle of Willis in newborns: color Doppler imaging of 53 healthy full-term infants.

To establish the usual pattern of flow in the circle of Willis in newborns, the authors scanned 53 healthy full-term infants within 3 days of birth with color Doppler imaging. All examinations were performed and images interpreted by the same experienced individuals. The basilar, internal carotid (ICA), and anterior and middle cerebral arteries were seen in all infants. Vertebral, posterior cerebral, superior cerebellar, and posterior communicating (PCoA) arteries were seen in most infants. PCoA flow was from the ICA toward the posterior cerebral artery in 73 (98.6%) of the 74 vessels that were seen. Flow in the anterior communicating artery was seen in six infants, indicating dependence of an anterior cerebral artery on contralateral ICA perfusion. Two pitfalls involving the distal portion of the ICA were noted: This vessel could be confused with the proximal portion of the anterior cerebral artery or cavernous sinus if real-time images were not interpreted carefully. Variant patterns of flow included tortuous basilar arteries (n = 2), reversed PCoA flow (n = 1), and inferior angulation of the proximal portions of the anterior cerebral arteries (n = 2). Color Doppler imaging allows a detailed analysis of the circle of Willis in newborns and detection of some anatomic variations.

Cerebral Arteries↗
PubMed1989

Rotator cuff tears: prospective comparison of MR imaging with arthrography, sonography, and surgery.

Thirty-eight patients with suspected rotator cuff tears were examined at 1.5 T by using a loop-gap resonator surface coil. The MR findings were compared prospectively in a blinded fashion with the results from double-contrast arthrography in all 38 patients, high-resolution sonography in 23 patients, and surgery in 16 patients. In the total group of 38 patients, MR imaging detected 22 of 22 tears and 14 of 16 intact cuffs as determined by arthrography. In the 16 surgically proved cases, MR and arthrography showed identical results, with 92% sensitivity in the diagnosis of 12 tears and 100% specificity in the diagnosis of four intact cuffs. In a subgroup of 23 patients, sonography detected nine of 15 tears and seven of eight intact cuffs as determined by comparison with arthrography. In 10 surgically proved cases, sonography was 63% sensitive in the diagnosis of eight rotator cuff tears and 50% specific in the diagnosis of two intact cuffs. For the diagnosis of rotator cuff tears, MR imaging is comparable to arthrography in both sensitivity and specificity. In this study, sonography was not as accurate in the diagnosis of rotator cuff tears as were the other two techniques. These results suggest that MR imaging should be considered the noninvasive test of choice for patients with suspected rotator cuff disease.

Arthrography↗
PubMed1989

Sampling bandwidth and fat suppression: effects on long TR/TE MR imaging of the abdomen and pelvis at 1.5 T.

In MR imaging, the sampling bandwidth is the rate at which the signal is digitized by the analog-to-digital converter. Reducing the sampling bandwidth can decrease noise in long TE images at the expense of increases in the artifacts of chemical-shift misregistration and motion. We compared 39 pairs of axial images with bandwidths of 32 kHz and 8-10 kHz. In 23 of these comparison studies (six female pelvis, seven male pelvis, 10 abdomen), all other variables were held constant, and in 16 comparisons (10 female pelvis, six male pelvis), signal from fat was suppressed in images with reduced bandwidth. Six patients with 11 liver lesions were included in those undergoing abdominal imaging. In three patients, fat was suppressed in images of the abdomen. The contrast-to-noise ratio was greater with reduced bandwidth for urine vs fat (24.5 vs 17.2; p less than .05) and central vs peripheral parts of the prostate gland (34.1 vs 22.7; p less than .02). In the abdomen, the contrast-to-noise ratio was increased between liver and right kidney (36.6 vs 25.2; p less than .01) and between liver and lesion (30.2 vs 18.2; p less than .005), but the motion-induced artifact was worse. An increase in chemical-shift misregistration did not affect the appearance of the internal structure of the uterus, prostate gland, or liver, but it made examination of the ovaries, seminal vesicles, and extrahepatic tissues difficult. The chemical-shift artifact in pelvic images could be eliminated by suppressing signal from fat with frequency-selective saturation pulses, but results were less satisfactory in the abdomen. When reduced bandwidth and fat suppression were combined, the contrast-to-noise ratio was improved for endometrium vs myometrium (22.9 vs 15.2; p less than .05) and central vs peripheral parts of the prostate gland (62.7 vs 28.5; p less than .02). Reduction of the sampling bandwidth is a promising technique for imaging the pelvis with small field of view and long TR/TE, but it currently appears less promising for images in the upper abdomen at 1.5 T. The increased chemical-shift artifact caused by reduced bandwidth can be eliminated by suppressing signal from fat.

Abdomen↗
PubMed1989

Hand-held and automated sonomammography. Clinical role relative to X-ray mammography.

A retrospective analysis of 73 patients who had undergone X-ray mammography (XRM), automated sonomammography (ASM), and hand-held sonomammography (HSM) was performed to evaluate the clinical role of both types of sonomammography (SM) relative to XRM. The results were classified on the basis of mammographic and sonographic findings. Clinical and/or surgical proof was obtained in all 73 patients. The SM was complementary to XRM, depending on the radiographic breast density. When comparison was made between ASM (4.5 MHz) and the HSM (7.5 MHz), the pathologic condition was better identified by HSM in 86% of the cases. Moreover, in no cases was ASM better than HSM.

Adult↗
PubMed1989

Magnetic resonance imaging of the ischemic hip. Alterations within the osteonecrotic, viable, and reactive zones.

To explore the ability of magnetic resonance imaging (MRI) to depict the morphologic features of avascular necrosis (AVN) of the femoral head and to determine whether a classification based on stage of necrosis is possible, images of hips with 56 proved lesions were examined and correlated with roentgenographic stage, severity of pain and functional impairment, and available computed tomography (CT) scans. Six femoral heads with AVN were also studied ex vivo with MRI, CT, roentgenographic, and histologic examinations. These examinations were compared with 100 normal hips in 50 individuals and one normal proximal femoral specimen. The reactive interface between live and dead bone at the periphery of AVN lesions had a characteristic MRI appearance that facilitated diagnosis. Based on central signal intensity on two different pulse sequences, lesions could be separated into four classes that correlated with roentgenographic and clinical staging. Lesions that were isointense with fat on both sequences had an earlier roentgenographic stage and less severe symptoms than did lesions that were less intense than fat. Among hips with AVN in patients younger than 50 years of age, 67% had premature conversion to fatty intertrochanteric marrow outside the borders of the lesion. Detecting premature conversion to fatty marrow has important implications regarding the pathogenesis of AVN and may aid early diagnosis. MRI provides pathophysiologic information that is different from information obtained from conventional methods or various combinations of methods and may provide a basis for an improved system for grading AVN lesions.

Adult↗
PubMed1988

Neonatal brain: color Doppler imaging. Part I. Technique and vascular anatomy.

Color Doppler imaging (CDI) can demonstrate the relative direction and velocity of blood flow in color, superimposed on a conventional gray-scale ultrasound image that depicts stationary tissue. Twenty-five infants were studied with portable CDI in the coronal, sagittal, and axial planes. Bilateral antegrade flow was noted in the anterior, middle, and posterior cerebral arteries in all patients. Multiplanar CDI can image flow in the circle of Willis and its tributaries and branches.

Arteries↗
PubMed1988

Neonatal brain: color Doppler imaging. Part II. Altered flow patterns from extracorporeal membrane oxygenation.

Extracorporeal membrane oxygenation (ECMO), a lifesaving procedure in neonates with severely impaired lung function, requires ligation of the right common carotid artery. In an investigation of the collateral pathways that maintain perfusion of the brain after right common carotid artery ligation, ten infants were studied with color Doppler imaging during and after ECMO. The circle of Willis was seen in all infants, and in every case there was retrograde flow in the distal internal carotid artery and the proximal (A1) segment of the anterior cerebral artery. Bilateral flow in the middle cerebral arteries and in distal branches of the anterior cerebral arteries was also seen, documenting flow to both cerebral hemispheres.

Carotid Arteries↗
PubMed1988

Low-artifact intravascular devices: MR imaging evaluation.

Flow-phantom magnetic resonance (MR) imaging, with use of both spin-echo (SE) and gradient-echo (GRE) techniques at 1.5 T, was performed on the percutaneous Greenfield (beta-III titanium alloy [TMA wire]), Amplatz (MP32-N alloy), and Simon nitinol filters and TMA wire facsimiles of the bird's nest, Gunther, new retrievable, and Amplatz vena caval filters. SE imaging allowed detection of thrombi as small as 5 X 5 mm trapped within the percutaneous Greenfield, Simon nitinol, and TMA-wire facsimile filters; with the MP32-N Amplatz filter, a larger volume of thrombus (10 X 20-mm clots) was necessary for clot detection. GRE imaging allowed detection of intraluminal tilting of the percutaneous Greenfield and facsimile Amplatz (TMA-wire) filters. GRE imaging was useful for demonstrating postfilter turbulence due to clots, which was greatest for the Amplatz filter. Imaging of facsimile vascular devices made of tantalum or TMA wire did not cause the severe "black-hole" MR artifacts typical of the stainless-steel devices. SE and GRE imaging were very useful for determining caval patency in two patients with previously placed Mobin-Uddin filters. Noninvasive MR evaluation of blood vessels in the presence of a variety of low-artifact intravascular devices appears feasible.

Blood Vessel Prosthesis↗
PubMed1988

Motion artifact reduction in MR imaging of the abdomen: gradient moment nulling versus respiratory-sorted phase encoding.

Two currently available methods of reducing motion-induced artifact on magnetic resonance (MR) images, respiratory-sorted phase encoding (RSPE) and gradient moment nulling (GMN), were compared in images of the upper abdomen obtained with long repetition and long echo times. For ten subjects, two series of axial MR images were obtained with identical parameters except that RSPE was used in one and GMN in the other. Images were evaluated by three independent radiologists, and region-of-interest measurements were obtained to calculate signal-difference-to-noise ratios (SD/Ns) for liver versus gallbladder and liver versus the right kidney. Maximum ghost intensity and the standard deviation of motion-induced noise were also calculated. GMN was superior to RSPE for motion artifact reduction in all ten cases. The SD/N for liver versus both gallbladder and right kidney was significantly higher with GMN. Presaturation pulses applied outside the volume of interest reduced aortic and inferior vena cava signal and virtually eliminated artifact from these vessels but did not noticeably affect signal from intrahepatic vessels. GMN combined with presaturation pulses is a highly effective method of motion artifact reduction in the upper abdomen.

Abdomen↗
PubMed1988

Urachal carcinoma: CT findings.

The computed tomographic (CT) appearance of urachal carcinoma in ten patients was studied and compared with the pathologic findings. Magnetic resonance images were available in one case. All tumors were mucinous adenocarcinomas; four were solid, three were cystic, and three were mixed. The tumor had a characteristic location along the expected midline course of the urachus directly behind the anterior abdominal wall. The main tumor mass was supravesical in eight patients. Seven tumors contained calcification. CT correctly depicted bladder wall involvement and supravesical extent of tumor in all cases. CT provided incorrect information about invasion of the perivesical fat in three patients and about bladder mucosal invasion in two patients.

Adenocarcinoma, Mucinous↗
PubMed1988

Ultrasound for guidance of breast mass removal.

Hand-held sonomammography was used intraoperatively to localize 52 masses in 45 women in an out patient operating suite. All but five women had a positive X-ray mammogram. The ultrasound mammogram was able to identify all lesions. In 42 women studied by a preoperative ultrasound examination before the operating room procedure, all the masses were successfully identified. Precise localization was successfully performed in the operating room before sterile preparation in less than 10 minutes. Relocalization after incision in the sterile operating field was necessary in two cases. This technique requires no ionizing radiation and expedites outpatient surgical removal of the lesion. Of the 52 masses, there were 32 fibroadenomas, three carcinomas, three cysts, six cases of focal fibrous mastitis, and eight patients with focal fibrocystic disease. In patients with positive sonograms for nonpalpable masses, ultrasound localization is a fast, accurate alternative to X-ray needle placement.

Adenofibroma↗