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Biomedical subjects

D G Mitchell

Publications and source records attributed to D G Mitchell.

At least 127 records · Page 7Linked to original sources
PubMed1992

Neurodevelopment of preterm infants: neonatal neurosonographic and serum bilirubin studies.

In this study of 249 preterm infants of less than 34 weeks' gestation, the relationships between maximal serum total bilirubin concentrations during the neonatal period, neonatal cranial ultrasonographic abnormalities, and severe neurodevelopmental sequelae are described. The subjects, who were selected on the basis of serial cranial ultrasonographic findings, had repeated neurologic and developmental examinations during late infancy and early childhood that established the presence (n = 45) or absence (n = 204) of spastic forms of cerebral palsy. Of the 204 subjects without cerebral palsy, 23 scored abnormally low on standardized developmental testing during early childhood. All but seven of the subjects with cerebral palsy had grade III/IV intracranial hemorrhage or moderate to severe periventricular echogenicity or both, ultrasonographic abnormalities that probably reflect a disruption in the blood-brain barrier as well as extravasation of blood into brain tissue; however, analysis of the data did not suggest that these cranial ultrasonographic abnormalities increased either the maximum serum bilirubin concentration during the neonatal period or the susceptibility of the subjects to neurologic damage from hyperbilirubinemia. Also, there was no evidence to suggest that bilirubinemia in the range studied (2.3 to 22.5 mg/100 mL total serum bilirubin) was causally related to cerebral palsy, early developmental delay, or the development of periventricular cysts in this population of preterm infants.(ABSTRACT TRUNCATED AT 250 WORDS)

Apgar Score↗
PubMed1992

Mechanical ventilation in preterm infants: neurosonographic and developmental studies.

Surviving preterm infants of less than 34 weeks' gestation who were selected on the basis of serial cranial ultrasonographic findings during their nursery course had repeated neurologic and developmental examinations during late infancy and early childhood that established the presence (n = 46) or absence (n = 205) of spastic forms of cerebral palsy. Of the 205 infants without cerebral palsy, 22 scored abnormally low on standardized developmental testing during early childhood. The need for mechanical ventilation beginning on the first day of life (n = 92) was significantly related to gestational age, birth weight, Apgar scores, patent ductus arteriosus, grade III/IV intracranial hemorrhage, large periventricular cysts, and the development of cerebral palsy. In the 192 mechanically ventilated infants, vaginal bleeding during the third trimester, low Apgar scores, and maximally low PCO2 values during the first 3 days of life were significantly related to large periventricular cysts (n = 41) and cerebral palsy (n = 43), but not to developmental delay in the absence of cerebral palsy (n = 18). The severity of intracranial hemorrhage in mechanically ventilated infants was significantly associated with gestational age and maximally low measurements of PCO2 and pH, but not with Apgar scores or maximally low measurements of PO2. Logistic regression analyses controlling for possible confounding variables disclosed that PCO2 values of less than 17 mm Hg during the first 3 days of life in mechanically ventilated infants were associated with a significantly increased risk of moderate to severe periventricular echodensity, large periventricular cysts, grade III/IV intracranial hemorrhage, and cerebral palsy. Neurosonographic abnormalities were highly predictive of cerebral palsy independent of PCO2 measurements.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain Diseases↗
PubMed1992

Abdominal magnetic resonance imaging: optimization and artifact suppression.

Optimized spin-echo images must contain adequate tissue contrast, which can be realized by selecting proper repetition time, echo time, and flip angle. Although conventional T2-weighted images have long acquisition time and limited signal-to-noise ratio (SNR), multiecho conjugate techniques address both of these problems, SNR, resolution, and anatomic coverage are interrelated issues that must be addressed together. Motion artifact reduction techniques include averaging, physiologic monitoring, gradient-moment nulling, spatial presaturation, and fat suppression. Best results are obtained by combining multiple methods when possible.

Abdomen↗
PubMed1992

Chemical shift magnetic resonance imaging: applications in the abdomen and pelvis.

Chemical shift imaging allows unambiguous separation of lipid and water signals. Useful images include opposed-phase (water minus fat) and fat-suppressed images, which can be obtained with spin-echo or gradient-echo methods. Chemical shift techniques can be used to reduce artifacts, to expand dynamic range, to diagnose fatty infiltration of the liver, to distinguish between benign and malignant adrenal lesions, and to diagnose benign teratomas in women.

Adrenal Cortex Diseases↗
PubMed1992

Benign disease of the uterus and ovaries. Applications of magnetic resonance imaging.

Because of its relatively low cost, widespread availability, and patient tolerance ultrasound remains the primary modality for imaging the female pelvis. Nevertheless, MR imaging can contribute to cost-effective management in women who have suspected myomas or adenomyosis by establishing the diagnosis noninvasively. It can also improve management and reduce costs by providing precise presurgical mapping prior to myomectomy or correction of müllerian duct anomalies. In these instances, other tests such as hysterosalpingography and laparoscopy may be obviated if fallopian tube disease is not strongly suspected. MR imaging is also valuable in patients in whom suspected adnexal masses are not detected sonographically or in whom definitive diagnosis of juxta-uterine myoma, cystic teratoma, or hemorrhagic mass may alter management.

Female↗
PubMed1991

Color Doppler imaging of the eye and orbit. Technique and normal vascular anatomy.

Color Doppler imaging is a recent advance in ultrasonography that allows simultaneous two-dimensional imaging of structure and blood flow to be performed. Doppler information is superimposed in color over a conventional gray-scale ultrasound image. Using this technique, we examined 40 normal eyes. The central retinal artery, posterior ciliary arteries, ophthalmic artery, and central retinal vein could be located in all patients. Using the color image as a guide, Doppler spectral analysis allows quantitative assessment of blood flow velocity in these vessels. Color Doppler imaging is a new modality for the study of ocular and orbital hemodynamics.

Adult↗
PubMed1991

Color Doppler ultrasound imaging in iatrogenic arterial injuries.

Pulsatile masses following arterial puncture for diagnostic or therapeutic procedures may represent false aneurysms or noncommunicating periarterial hematomas with transmitted arterial pulsation. Color Doppler ultrasound imaging was used in 27 patients with pulsatile groin masses. Of these 27 patients, 23 were diagnosed as having pseudoaneurysms and 5 as having periarterial hematomas. The pseudoaneurysms were confirmed at surgical exploration, and the periarterial hematomas were all observed longitudinally with spontaneous resolution. With a sensitivity of 100% and a specificity of 100% in this clinical study, color Doppler ultrasound imaging appears to be the diagnostic modality of choice for detecting false aneurysms following transarterial procedures, obviating the need for additional invasive diagnostic procedures.

Aneurysm↗
PubMed1991

Hepatocellular carcinoma within siderotic regenerative nodules: appearance as a nodule within a nodule on MR images.

Large regenerative nodules in cirrhotic livers may accumulate iron and develop internal iron-poor foci of hyperplasia or malignancy. Magnetic resonance examinations were performed on 23 patients with biopsy-proved cirrhosis. A "nodule-within-nodule" appearance was noted in two patients. This appearance consisted of markedly low intensity of a large nodule on gradient-echo images, with one or two internal foci that were isointense to the liver. Each of the large nodules was 2 cm in diameter, and each of the internal foci was less than 1 cm. Serum alpha-fetoprotein levels were normal in both patients. Aspiration biopsy performed in one patient failed to show malignancy, but histologic confirmation of hepatocellular carcinoma was obtained eventually in both cases. The nodule-within-nodule sign, which reflects the unique histopathology of hepatocellular carcinoma in large siderotic regenerative nodules, is strongly suggestive of early hepatocellular carcinoma, even if serologic markers and biopsy results do not support this diagnosis.

Biopsy↗
PubMed1991

Liver and pancreas: improved spin-echo T1 contrast by shorter echo time and fat suppression at 1.5 T.

T1-weighted spin-echo magnetic resonance (MR) images have had limited soft-tissue contrast at 1.5 T. The authors investigated the effects of echo-time (TE) minimization and fat suppression on MR images of the liver and pancreas. Two sets of MR images were obtained with identical repetition times and other parameters. In 10 subjects with seven liver lesions, images with TEs of 20 and 12 msec were compared. In 18 additional subjects with seven liver lesions and five pancreatic carcinomas, images with identical TEs but with and without fat suppression were compared. Contrast-to-noise ratios (CNRs) were greater with a TE of 12 msec than with a TE of 20 msec for liver versus spleen (7.6 vs 4.9, P = .014) and liver versus lesion (6.9 vs 3.9, P = .031). In patients without fatty liver, CNR for six lesions versus liver was greater (9.5 vs 6.0, P = .014) with fat suppression. CNR between glandular pancreas and cancer was most conspicuous with fat suppression, but fat planes were less distinct. Minimization of TE improves T1-weighted images significantly. Fat suppression also improves CNR, but the disadvantages of fat suppression do not allow elimination of conventional T1-weighted images.

Fatty Liver↗
PubMed1991

Parenchymal versus reticuloendothelial iron overload in the liver: distinction with MR imaging.

Parenchymal iron deposition occurs in hemochromatosis, while iron is deposited in reticuloendothelial (RE) cells after blood transfusions or rhabdomyolysis. Magnetic resonance images of patients with decreased liver signal intensity on T2-weighted images at 1.5 T were blindly compared in an effort to distinguish these conditions. In each of five patients with hemochromatosis, the pancreas had low signal intensity, but splenic signal intensity was decreased in only one. In contrast, only three of the 16 patients with RE iron overload had low pancreatic signal intensity, while all of these patients either had low splenic signal intensity (n = 14) or previously underwent splenectomy (n = 2). Distinction among these causes of iron deposition is clinically important because parenchymal iron overload from hemochromatosis may produce significant tissue damage, while the RE iron of transfusions and rhabdomyolysis is of little clinical consequence.

Adolescent↗
PubMed1991

Comparison of Kaopectate with barium for negative and positive enteric contrast at MR imaging.

In an evaluation of safe, inexpensive, orally administered contrast agents for use at magnetic resonance imaging, different concentrations of the clay agents kaolin-pectate and attapulgite were compared in an in vitro phantom by performing spin-echo imaging with variable echo times to estimate T2 relaxation time. Additional phantoms containing from 0% to 100% attapulgite or barium preparations were compared by using spin-echo and spoiled-gradient-echo techniques to estimate T1, T2, and T2* relaxation times. In vivo spin-echo and gradient-echo images were obtained of 10 healthy volunteers and of five patients with pancreatic disease after oral administration of 12-16 oz of attapulgite preparation. T1 and T2 relaxation times obtained with use of attapulgite were slightly lower than those obtained with kaolin-pectate at both 50% and 25% concentrations. Compared with barium, attapulgite had shorter T1, T2, and T2* relaxation times, and concentration-dependent relaxivity was greater by nearly an order of magnitude. All subjects were able to drink the attapulgite, and the only complaints were of bad taste and mildly loose stools.

Barium Sulfate↗
PubMed1991

Frontal periventricular cysts on the first day of life. A one-year clinical follow-up and its significance.

During a 6-year period, the prospective interpretations of routine screening cranial ultrasound on 1453 premature infants indicated frontal periventricular cysts in 7 infants without other intracranial abnormalities during the first 24 hours after birth. The medical records of these 7 infants and their mothers and a developmental assessment at age 1 year were also reviewed. The cysts were predominantly single and unilateral and ranged in size from 2 to 11 mm. One infant had bilateral subependymal cysts as well as frontal periventricular cysts. All 7 infants before 1 year of age demonstrated mild neurological deficiencies. However, 6 of 7 demonstrated partial or complete resolution of their neurological impairment by the end of 1 year. One infant was lost to clinical follow-up. The presence of these frontal periventricular cysts in the first 24 hours after birth suggests an in-utero event, such as antepartum hemorrhagic infarction, as their etiology.

Brain Diseases↗
PubMed1991

Fatty liver. Chemical shift phase-difference and suppression magnetic resonance imaging techniques in animals, phantoms, and humans.

In vitro animal and human models were used to evaluate the potential of chemical shift magnetic resonance imaging (MRI) for assessing fatty liver. Phantoms of varying fat content were created from mayonnaise-agar preparations. Fatty liver was induced in eight rats by feeding them ethanol for three to six weeks (36% of total calories), whereas eight control rats were fed a normal diet. T1-weighted in-phase and opposed-phase MR images were obtained of the phantoms animals, and 28 human subjects. Additional images obtained in animals included long TR images with in-phase and opposed-phase technique, and hybrid chemical shift water and fat suppression. The rats were killed and histologic status was graded blindly by a hepatopathologist as normal, mild, moderate, or severe fatty change, for correlation with MR grading. Quantitative analysis of MR images included fat signal fraction for animals, and relative signal decrease between in-phase and opposed-phase images for phantom and human data. Phantom in-phase signal increased linearly with respect to fat content, whereas opposed-phase signal decreased linearly. MRI and histologic grading of rat livers were highly correlated, especially when based on water suppression images (r = 0.91, P = .0001). Opposed-phase images were also highly correlated, while fat suppression images were less effective. There was no overlap between MR-derived fat fractions for control (2.6%-5.7%) versus ethanol-fed rats (7.7%-17.9%, P = .0002). Human liver considered to be fatty by visual inspection (n = 8) had higher relative signal decrease than nonfatty liver (n = 22) (P less than .001). Phantom, animal, and human data demonstrate that comparison of T1-weighted in-phase and opposed-phase images is both practical and sensitive in the detection and grading of fatty liver.

Adult↗
PubMed1990

MRI of aggressive fibromatosis: frequent appearance of high signal intensity on T2-weighted images.

Magnetic resonance imaging of seven patients with eight pathologically proven desmoid tumor tumors was performed and retrospectively reviewed. On T2-weighted images, all but one lesion demonstrated increased signal intensity relative to muscle, and had signal intensity similar to that of fat. The signal was heterogenous in six of these seven lesions. In a patient with synchronous multicentric lesions, light microscopy correlation revealed increased cellularity in one lesion with increased signal intensity and dense collagenous elements in a second lesion, with decreased signal intensity. High signal intensity appears to be typical but nonspecific, and in following these patients could indicate recurrent tumor, superimposed inflammatory process or granulation tissue.

Abdominal Neoplasms↗
PubMed1990

MR imaging of pulmonary parenchyma and emboli by paramagnetic and superparamagnetic contrast agents.

Using experimentally induced pulmonary emboli in an animal model, three intravenously administered contrast agents, Gd-DTPA-albumin microspheres (8-15 microns, 0.2 M particles/mg protein, 39-106 micrograms Gd/mg, 50 mg/ml), Gd-DTPA-liposomes (15-30 microns, 130 micrograms/mg lipid, 6 mg Gd/ml) and superparamagnetic ferrosome, (60 nm, 100 mM iron and 20 mg lipid/ml) were examined for MR imaging. Gd-DTPA entrapped in lung capillaries did not enhance the signal intensity of lung parenchyma, but liposomes (5 ml) served as better Gd-DTPA carriers and increased the parenchymal signal intensity by up to a factor of 2.3. However, neither agent improved delineation of pulmonary emboli. Ferrosome decreased the intensity of lung parenchyma, improving detectability of pulmonary emboli by several factors.

Animals↗
PubMed1990

Bone marrow findings on magnetic resonance images of the knee: accentuation by fat suppression.

Long TR/double spin-echo magnetic resonance images of the knee were obtained with and without the use of fat suppression techniques in seven patients with high signal intramedullary lesions. Comparison between images was performed qualitatively and quantitatively. Contrast-to-noise ratios between focal defects and surrounding fatty marrow were higher with fat suppression in all cases. The mean contrast-to-noise ratio for images obtained with fat suppression was 53.6, while for images obtained without fat suppression the mean contrast-to-noise ratio was 17.3 (p less than 0.01).

Adipose Tissue↗