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Biomedical subjects

D G Mitchell

Publications and source records attributed to D G Mitchell.

At least 109 records · Page 6Linked to original sources
PubMed1993

Use of Ferrum in MRI of lung parenchyma and pulmonary embolism.

MRI of lung parenchyma and pulmonary embolism (PE) remains challenging. "Ferrum," a ferric hydroxide sucrose complex used clinically for iron deficiency anemia for more than 40 years, was investigated as a negative MRI contrast agent in five rabbits bearing experimental PE as well as in five normal volunteers. Clots were prepared by spontaneous coagulation of 0.1 ml In-111 labeled autologous red blood cells and introduced through the jugular vein. Scintigraphic imaging permitted anatomical localization of PE in vivo and thereby served as a control for MR imaging. MRI was performed on a 1.5 T GE Signa scanner before and after induction of PE, and before and after the injection of Ferrum. T1-weighted images were obtained continuously for up to 90 min using varying doses of Ferrum. In five normal human volunteers, a single dose of 100 mg each was administered. T1- and T2-weighted spin-echo and gradient-echo images of lung parenchyma were repeatedly obtained before and after agent administration. In rabbit, Ferrum remained in circulation for several hours where it shortened both T1 and T2 of blood, improving the contrast between PE and lung parenchyma (i.e., intravascular compartment). A dose of 3 mg/kg was enough to increase the contrast-to-noise ratio (CNR) between PE and lung parenchyma by almost three fold, substantially improving lesion detectability. CNR increased up to five-fold when the dose was increased up to 20 mg/kg at which point CNR reached a plateau. In humans, T2-weighted spin-echo sequence appeared to be most sensitive to changes in signal-to-noise ratio (SNR) of normal lung parenchyma. Within 60 min after injection of 100 mg of iron, SNR dropped by 34% (p < .025). However, 24 hr later, SNR returned to almost normal. Ferrum increased the contrast between PE and lung parenchyma in the rabbit and decreased the parenchymal SNR in humans in nontoxic doses. These results suggest that Ferrum is worthy of further investigation of PE imaging in humans.

Aged↗
PubMed1993

Hooked acromion: prevalence on MR images of painful shoulders.

An association between the morphology of the acromion and the occurrence of rotator cuff tear (RCT) has been suggested by findings at both pathologic examination and routine radiography. As a tomographic technique, magnetic resonance (MR) assessment of acromial shape may be more accurate than routine radiography. The authors studied acromial morphology on sagittal oblique MR images of a control population (47 shoulders), of patients with isolated impingement (30 shoulders), and of patients with full-thickness RCTs (34 shoulders) to assess the association of acromial shape with disorders of the rotator cuff. Acromions were classified as flat (type 1), smoothly curved (type 2), or hooked (type 3). Data were collected by two observers, blinded to clinical and surgical information, who acted in consensus. Patients with RCT had a significantly increased prevalence of type 3 acromions compared with control patients (62% vs 13%, P < .001). Type 3 acromions tended to be more prevalent in the group with impingement (30%, P = .17). There was no significant difference in the distribution of acromion types among control patients with respect to age or gender.

Acromion↗
PubMed1993

Bull's-eyes and halos: useful MR discriminators of osseous metastases.

To evaluate the presence of (a) a focus of high signal intensity in the center of an osseous lesion (bull's-eye) as a negative discriminator for metastasis and (b) a rim of high signal intensity around an osseous lesion (halo) as a positive discriminator, a retrospective study was performed in 47 patients with osseous lesions suspect for metastatic disease who underwent magnetic resonance (MR) imaging of the pelvis. The findings in 17 patients with proved osseous metastasis were compared with those in 30 patients not believed to have metastatic disease; T1- and T2-weighted MR images were evaluated. The bull's-eye sign was found to be a specific indicator of normal hematopoietic marrow (sensitivity, 95%; specificity, 99.5%). The halo sign and diffuse signal hyperintensity were a strong indicator of metastatic disease (sensitivity, 75%; specificity, 99.5%). These results suggest that use of the bull's-eye sign as a discriminator of benign disease and use of the halo sign as a discriminator of metastasis help characterize suspect areas of marrow lesions.

Adult↗
PubMed1993

Idiopathic hemochromatosis: MR imaging findings in cirrhotic and precirrhotic patients.

The authors reviewed T2-weighted and T2*-weighted abdominal magnetic resonance (MR) images in 19 pathology-proved cases of hepatic iron overload to compare patterns of iron distribution among cirrhotic and precirrhotic patients with idiopathic hemochromatosis (IH), as well as nontransfusional hepatic siderosis of other causes. Fifteen patients had clinical and laboratory evidence of IH. Four patients without IH had cirrhosis with moderate siderosis. In the MR images of all 19 patients, the liver had low signal intensity. The pancreas of 10 of 11 cirrhotic patients with IH had low signal intensity. All four precirrhotic patients with IH and all four cirrhotic patients without IH had pancreas with normal signal intensity at MR. Thus, pancreatic signal intensity was decreased only in cirrhotic patients with IH in this limited series. Conversely, pancreatic signal intensity is often normal in precirrhotic patients with IH prior to the development of cirrhosis, a stage at which definitive diagnosis by means of quantitative liver biopsy is important because early phlebotomy may prevent morbidity and mortality from IH. In cirrhotic patients with MR evidence of increased hepatic iron, the cause of cirrhosis is less likely to be IH if pancreatic signal intensity is normal.

Adult↗
PubMed1993

Posterior tibial tendon tears: utility of secondary signs for MR imaging diagnosis.

To assess the range of appearance of both torn and normal posterior tibial tendons (PTTs) and to evaluate secondary signs related to abnormal biomechanics as aids in diagnosing PTT tears, 23 patients with complete PTT tears and 34 control patients were examined with magnetic resonance imaging at 1.5 T. Examiners were blinded to diagnosis. The diameter of the PTT was measured at the insertion and at the level of the ankle. The torn and control PTTs were bulbous distally (respective mean values, 6.2 mm vs 4.6 mm), with overlap in the range of tendon size. All PTTs also had overlap in the frequency of intra-tendon signal intensity (torn PTTs, 83%, vs control PTTs, 41%; T1-weighted, 61%, vs T2-weighted, 22%). The presence of a talonavicular abnormality was both a sensitive (82%) and specific (100%) sign of a PTT tear. The presence of medial tubercle hypertrophy (sensitivity, 89%; specificity, 75%) and an accessory navicular bone (sensitivity, 20%; specificity, 100%) were useful secondary signs of a complete PTT tear.

Adolescent↗
PubMed1993

Diagnosis of osteomyelitis: utility of fat-suppressed contrast-enhanced MR imaging.

PURPOSE: To assess the value of fat-suppressed contrast material-enhanced magnetic resonance (MR) imaging in the diagnosis of osteomyelitis. MATERIALS AND METHODS: T1- and T2-weighted MR imaging was performed in 51 cases of suspected osteomyelitis. Nonenhanced and contrast-enhanced T1-weighted fat-suppressed MR images were also obtained. Three-phase bone scan results were available for 30 cases. Complicating clinical factors, including chronic osteomyelitis (n = 26), postoperative state (n = 17), and neuropathic disease of the foot (n = 5), were identified in 73% of cases. RESULTS: In the diagnosis of osteomyelitis, scintigraphy demonstrated a sensitivity of 61% and specificity of 33%. For nonenhanced MR imaging, sensitivity was 79% and specificity was 53%. For fat-suppressed contrast-enhanced imaging, sensitivity was 88% and specificity was 93%. CONCLUSION: In diagnosing osteomyelitis in patients with complicating clinical factors, fat-suppressed contrast-enhanced MR imaging was significantly more sensitive than scintigraphy (P = .04) and significantly more specific than nonenhanced MR imaging (P = .02) or scintigraphy (P = .008).

Adipose Tissue↗
PubMed1993

Hepatic imaging: techniques and unique applications of magnetic resonance imaging.

The appropriate use of various MRI pulse sequences allows accurate detection and characterization of focal liver lesions. There are now a wide array of useful techniques for obtaining T1-weighted and T2-weighted images with or without suspended respiration. In the vast majority of cases, malignant liver lesions can be distinguished from hemangiomas or cysts, although contrast agents may be necessary. MRI can also definitively identify lipid and iron within hepatic parenchyma, increasing its usefulness for diagnosing and evaluating diffuse liver diseases. The expanded tissue contrast of MRI allows better differentiation of malignancies and "pseudotumors" due to diffuse liver disease. Appropriate two-dimensional time-of-flight techniques depict abdominal vessels clearly, allowing accurate detection or exclusion of hepatic vascular disorders. There is no other single method that can be used to examine the liver as comprehensively.

Contrast Media↗
PubMed1993

Magnetic resonance imaging of diffuse bone marrow disease.

MR is a highly sensitive alternative to plain films, CT, and radionuclide studies for the imaging of normal and abnormal marrow and can characterize differences between fatty, fibrotic, cellular, hypercellular, and hemosiderotic marrow. MR is helpful in depicting the extent of disease and has been a useful method to follow the clinical course of many disorders. It has been found to be particularly useful in explaining the unrepresentative biopsy, as the distribution of many diseases is frequently heterogeneous as exemplified by the mixed fatty and cellular patterns of aplastic anemia, myeloma, lymphoma, and skeletal metastases. Patterns of cellular and fatty marrow in the epiphysis and apophysis after marrow reconversion were not completely understood prior to the introduction of MR scanning. Because it has the advantage of imaging the entire bone marrow compartment (unlike the situation with biopsy on aspiration), MR allows a better understanding of the distribution of skeletal disease.

Bone Marrow↗
PubMed1992

Mass-like hepatic hypertrophy: MRI findings with histologic correlation.

Hepatic parenchyma may hypertrophy following asymmetrical injury. The histologic characteristics of hypertrophic hepatic parenchyma are more similar to normal hepatic parenchyma than is the more severely damaged liver. We present four cases where large hypertrophic masses resembled neoplasm on other imaging modalities or at surgery, but had MRI signal characteristics similar to those of normal liver.

Adult↗
PubMed1992

Partial angle inversion recovery (PAIR) MR imaging: spin-echo and snapshot implementation.

The effects of varying the inversion or excitation RF pulse flip angles on image contrast and imaging time have been investigated in IR imaging theoretically, with phantoms and with normal volunteers. Signal intensity in an IR pulse sequence as a function of excitation, inversion and refocusing pulse flip angles was calculated from the solution to the Bloch equations and was utilized to determine the contrast behavior of a lesion/liver model. Theoretical and experimental results were consistent with each other. With the TI chosen to suppress the fat signal, optimization of the excitation pulse flip angle results in an increase in lesion/liver contrast or allows reduction in imaging time which, in turn, can be traded for an increased number of averages. This, in normal volunteers, improved spleen/liver contrast-to-noise ratio (9.0 vs. 5.7, n = 8, p less than 0.01) and suppressed respiratory ghosts by 33% (p less than 0.01). Reducing or increasing the inversion pulse from 180 degrees results in shorter TI needed to null the signal from the tissue of interest. Although this decreases the contrast-to-noise ratio, it can substantially increase the number of sections which can be imaged per given TR in conventional IR imaging or during breathold in the snapshot IR (turboFLASH) technique. Thus, the optimization of RF pulses is useful in obtaining faster IR images, increasing the contrast and/or increasing the number of imaging planes.

Abdomen↗
PubMed1992

Right common carotid artery reconstruction in neonates after extracorporeal membrane oxygenation: color Doppler imaging.

Thirty-three neonates treated for reversible respiratory failure underwent reconstruction of their previously ligated right common carotid arteries (RCCAs) immediately after extracorporeal membrane oxygenation (ECMO). Cerebral color Doppler imaging, performed during and repeatedly after ECMO, revealed antegrade flow in the right internal carotid artery (ICA) in all neonates within 6 days after successful RCCA reconstruction. Mean ICA velocity was significantly less in the right artery compared with the left during ECMO and within 1 hour of reconstruction, but there was no difference after 12 hours. In neonates with successful RCCA reconstruction, the flow in the proximal right anterior cerebral artery was antegrade in only 4% of examinations during ECMO but became antegrade in 94% after 6 days. Retrograde flow in the right posterior communicating artery persisted in 50% of examinations performed 1 day after reconstruction. ICA flow become antegrade with symmetric velocities shortly after successful RCCA reconstruction. Collateral flow persists longer but decreases rapidly.

Blood Flow Velocity↗
PubMed1992

Cannula-induced vertebral steal in neonates during extracorporeal membrane oxygenation: detection with color Doppler US.

To determine whether flow through the subclavian artery might be affected during extracorporeal membrane oxygenation (ECMO), 40 neonates were examined with color Doppler ultrasound during and after ECMO. Retrograde flow in the right vertebral artery, noted in 12 of the 40 neonates (30%), was consistent with vertebral steal. Brachial systolic velocity was significantly less (P less than .01) on the right than on the left side in neonates both with and without vertebral steal. When the arterial cannula was removed after ECMO, vertebral artery flow became antegrade with symmetric velocity. Brachial velocities became symmetric in infants without vertebral steal, but mild asymmetry persisted in neonates who had had vertebral steal. Only one neonate had clinical signs of arm ischemia, which resolved promptly after removal of the cannula. No surviving neonates (n = 11) had neurologic findings related to the vertebrobasilar insufficiency over a 12-22-month period of observation. Vertebral steal appears to be common during ECMO and is resolved after removal of the cannula.

Basilar Artery↗
PubMed1992

Polycythemia vera and myelofibrosis: correlation of MR imaging, clinical, and laboratory findings.

Magnetic resonance (MR) imaging was performed in 14 patients with biopsy-proved polycythemia vera (n = 4) or myelofibrosis (n = 10) to determine whether MR imaging findings can be correlated with the clinicopathologic diagnosis and established clinical parameters of severity (serum lactate dehydrogenase [LDH] and cholesterol levels) and chronicity (spleen size). Evaluation of marrow in the proximal femurs showed that patients could be categorized into three distinct groups based on anatomic patterns of normal fatty and abnormal low-signal-intensity (non-fatty) marrow in the femoral capital epiphysis (FCE) and greater trochanter (GT). Patients with nonfatty marrow in both the FCE and GT (n = 8) had significantly higher serum LDH (P less than .02) and lower serum cholesterol (P less than .02) levels than patients with fatty marrow in at least the GT (n = 6). Splenic volume, as measured from MR images, was significantly greater in the myelofibrosis group than in the polycythemia vera group (P less than .001). MR imaging provided a better understanding of these hematologic disorders and novel parameters for classification that are different from conventional histologic and laboratory data.

Adult↗
PubMed1992

Focal manifestations of diffuse liver disease at MR imaging.

Detection and exclusion of focal liver lesions is especially difficult in patients with diffuse liver disease. Magnetic resonance (MR) imaging may be particularly valuable in these patients. By judicious comparison of appropriate pulse sequences, normal and hypertrophic liver may be distinguished from atrophic, neoplastic, or otherwise abnormal hepatic parenchyma. Chemical shift (lipid-sensitive) techniques allow definitive identification of fatty liver, including focal fatty infiltration or focal sparing. T2-weighted and T2*-weighted images allow identification of iron overload, depicting malignancies as focal masses without iron. Analysis of signal intensity and internal morphology allows confident distinction between regenerative nodules and hepatocellular carcinoma in most instances, and allows diagnosis of early carcinoma within regenerative nodules. MR imaging provides capabilities for noninvasive characterization of liver tissue beyond those available with other noninvasive modalities.

Budd-Chiari Syndrome↗
PubMed1992

Benign adrenocortical masses: diagnosis with chemical shift MR imaging.

Benign adrenocortical masses often contain lipid; metastases and pheochromocytomas do not. Standard and lipid-sensitive (chemical shift) magnetic resonance (MR) images of the adrenal glands in 31 patients with 45 adrenal masses were reviewed to determine if simple visual analysis of these images would increase diagnostic specificity. Lipid was considered present if signal intensity of the adrenal mass relative to other tissues decreased on chemical shift images relative to comparable standard images. Both myelolipomas and 26 of 27 benign cortical masses displayed a loss of signal intensity on at least one chemical shift image; all 12 metastases, the three hemorrhages, and a cyst did not. Opposed-phase images were slightly more sensitive than fat-suppressed images in depicting lipid within benign cortical masses. All masses had higher signal intensity than that of the liver on standard T2-weighted MR images. Chemical shift MR imaging can demonstrate lipid within benign adrenocortical masses and thus increase specificity, potentially obviating biopsy and aggressive follow-up.

Adenoma↗
PubMed1992

Pancreatic disease: findings on state-of-the-art MR images.

Recent technical innovations have made MR imaging a useful technique for imaging the pancreas. The potential impact of MR imaging on the management and outcome of cases can be determined only by controlled prospective comparative studies; however, these cannot be performed adequately until the normal and abnormal appearances of the pancreas on state-of-the-art MR images are understood. This pictorial essay is presented to further this intermediate goal.

Adenocarcinoma↗