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M Schnall

Publications and source records attributed to M Schnall.

31 records · Page 2Linked to original sources
PubMed1987

Cardiac transfer function relating energy metabolism to workload in different species as studied with 31P NMR.

Cardiac metabolism was studied with 31P NMR in 7 dogs and 4 cats to determine whether animals adapted for different life-styles (stalk and sprint vs endurance running) respond to increased work loads (heart rate X blood pressure product) with different high-energy phosphate kinetics. Hearts were exposed via a left lateral thoracotomy under Nembutal anesthesia (40 mg/kg). Two-turned solenoid surface coils were placed on the left ventricles; pacing wires were sutured into the left ventricular apices. The femoral artery and vein were cannulated for blood pressure and arterial blood gas monitoring and fluid and drug infusion, respectively. Animals were placed in a plexiglass holder into a 2.1-T, 31-cm-bore, superconducting magnet. 31P spectra were obtained from the heart using respiratory and electrocardiogram gating. Cardiac work loads were changed by pacing the heart at 4, 4.5, and 5 Hz. Heart rate X blood pressure product "work" was correlated with Pi/PCr ratios. Dog hearts were more resistant than those of cats to changes in Pi/PCr with increasing work load. It is possible that animals adapted to different life-styles may have cardiovascular systems which are metabolically and mechanically adapted for different forms of stress. These differences may be elicited and effectively delineated using in vivo NMR techniques during various physiological interventions, such as pacing. The basis for these differences may be related to cardiac microvasculature or to intrinsic differences in enzyme kinetics. Delineation of these mechanisms may be helpful in the understanding of the physiological basis of cardiac function in health and disease.

Adaptation, Physiological↗
PubMed1987

Simultaneous 31P- and 1H-nuclear magnetic resonance studies of hypoxia and ischemia in the cat brain.

The objective of this study was to evaluate simultaneous 31P/1H nuclear magnetic resonance (NMR) spectroscopy as a technique for monitoring and correlating changes in brain energy metabolism during hypoxia and ischemia. Five cats were studied with a protocol that involved 20 min of hypoxia (PaO2 20 mm), 60 min of recovery, 10 min of hypoxia with relative ischemia (bilateral carotid occlusion, PaO2 20 mm), and 60 min of recovery. Bifrontal and biparietal electrocorticograms (ECoG) were monitored continuously during the entire protocol. The results demonstrate that the degree of metabolic response is different in individual cats, but a number of quantitative relationships between metabolic parameters are consistently observed for all cats. First, there is agreement between increases in lactate and changes in intracellular pH; the observed relationship corresponds to an in vivo cerebral buffer capacity of 29 mumol/g/pH unit. Second, the delayed recovery of PCr is due to the effect of metabolic acidosis on the creatine kinase equilibrium and not to a delayed recovery of the ATP/ADP ratio. Third, the observed rate of lactate clearance from the cell is zero-order (k = 0.36 mumol/g/min) for lactate levels greater than 5 microns/g and may be composed of both lactate efflux from the cell and lactate oxidation.

Adenosine Triphosphate↗
PubMed1986

Myocardial high energy phosphate metabolism in closed chest dog: creation of an animal model.

A chronic closed chest dog model was developed to study myocardial metabolism with NMR spectroscopy. Cardiac windows were surgically created in 10 dogs by removal of two ribs and accompanying skeletal muscle. Marlex mesh was sewn between the two exposed ribs, and fascia and skin were closed. 31P spectra were obtained using a surface coil placed into the surgically created pouch and using routine NMR pulsing techniques.

Adenosine Triphosphate↗
PubMedDate not supplied

Endorectal surface coil MR imaging as a staging technique for rectal carcinoma: a comparison study to rectal endosonography.

BACKGROUND: Preoperative staging of rectal cancer is critical for guiding therapy and prescribing the most appropriate treatment option. The purpose of this investigation was to compare the accuracy of endorectal surface coil magnetic resonance imaging (ERSCMRI) with endosonography (EUS) in staging rectal lesions. METHODS: Fourteen patients with rectal carcinoma, initially detected by barium enema or sigmoidoscopy underwent ERSCMRI and EUS. Subsequent resection of the lesions was performed, and the staging accuracies of these two modalities are compared. RESULTS: MR T-staging agreement with pathologic T-staging was similar to that of EUS, but MR enabled more accurate identification of nodal involvement. CONCLUSION: ERSCMRI produced greater overall accuracy in staging for rectal carcinoma than did EUS.

Adenocarcinoma↗
PubMedDate not supplied

Proton MR spectroscopy of experimental radiation-induced white matter injury.

We studied the spectroscopic appearance of radiation-induced myelinolysis in cats to understand the characteristics of proton MR spectroscopy of demyelinating disorders. Eight cats received 5,000 rads to a 1.5 x 1.5 cm area of the right cerebral hemisphere. Eight to 9 months after irradiation, a gross area of abnormal postcontrast enhancement and/or high MR signal intensity was detected in the irradiated hemisphere of six of the eight cats. Proton spectra of a 1.0 cm3 voxel in the affected region demonstrated depressed N-acetyl aspartate/creatine-phosphocreatine and N-acetyl aspartate/choline-containing compound peak ratios compared with the contralateral non-irradiated brain in all cats. Elevated amino acid resonances in the 2.0-2.5 ppm range were not consistently seen in irradiated zones of the brain with pathologic findings of demyelination. In vivo proton MR spectroscopy may show differences between irradiated brain and nonirradiated brain even when histopathologic lesions are not apparent yet.

Amino Acids↗
PubMedDate not supplied

MR appearance of uterine dehiscence in the post-cesarean section patient.

PURPOSE: CT has been shown to be unreliable for detecting uterine dehiscence in the postoperative period after cesarean section (c-section). The purpose of this investigation is to describe the MR appearance of uterine dehiscence in this setting and identify features that distinguish complete from partial dehiscence. METHOD: Over an 82 month period, all charts and MR reports of patients that underwent MRI of the pelvis after c-section were reviewed for uterine dehiscence. Altogether, 55 patients were imaged. Positive cases for dehiscence were retrospectively reviewed by two radiologists. Imaging criteria for complete dehiscence consisted of transmural disruption. Criteria for partial dehiscence consisted of disruption of the endometrial and/or serosal layer, without transmural extension. RESULTS: On MRI, five patients demonstrated abnormalities suggestive of incisional dehiscence. Based on these imaging criteria, two of these showed complete dehiscence that was proven at surgery and three showed findings of partial dehiscence. The optimal imaging plane was perpendicular to the incision. CONCLUSION: MR features may be utilized to identify total uterine dehiscence and may be more effective than CT.

Adolescent↗
PubMedDate not supplied

Role of percent positive biopsies and endorectal coil MRI in predicting prognosis in intermediate-risk prostate cancer patients.

PURPOSE: This study was performed to determine the clinical factors that can optimize preoperative staging for clinically localized intermediate-risk prostate cancer patients. MATERIALS AND METHODS: Logistic and Cox regression multivariable analyses were performed on 480 prostate cancer patients whose disease was confined to the prostate to evaluate the ability of clinical stage, prostate-specific antigen (PSA), biopsy Gleason sum, percent positive biopsies, and endorectal coil magnetic resonance imaging (MRI) results to predict pathologic established extracapsular extension, seminal vesicle invasion, and time to postoperative PSA failure in patients with clinically localized prostate cancer. Intermediate risk was defined as PSA 4-10 ng/mL and Gleason sum 5-7; PSA 10-20 ng/mL and Gleason sum < or = 7. RESULTS: Intermediate-risk patients with at least 50%, 67%, 83%, or 100% positive biopsies have disease pathologically confined to the prostate at least 45% of the time; however, if an endorectal coil MRI is positive for either capsular penetration or seminal vesicle invasion, no more than 29% of patients have pathologically determined organ-confined disease. No intermediate-risk patient with both a positive MRI and at least 50% positive biopsies had pathologically determined organ-confined disease. Intermediate-risk patients with less than 50% positive biopsies had pathologically determined organ-confined disease in at least 77% of the cases. CONCLUSIONS: Intermediate-risk patients with an endorectal coil MRI showing extracapsular extension or seminal vesticle invasion are at high risk for early postoperative PSA failure. The concomitant presence of at least 50% positive biopsies increases this risk to unity. Therefore, these patients are not good candidates for surgery alone because of their high risk of extraprostatic disease and should be considered for entry onto phase III trials examining the effect of adding androgen-deprivation therapy to definitive local therapy (external-beam radiation therapy or surgery) on overall survival. The subgroup of intermediate-risk patients likely to benefit from an endorectal coil MRI are those patients with PSA > 10-20 ng/mL; biopsy Gleason score < or = 7, and at least 50% positive biopsies representing approximately 7.5% of the total patient population.

Biopsy↗