Biomedical subjects
Publications and source records attributed to M Viamonte.
The uses of various imaging modalities in the brain, spine, pelvis, chest, and abdomen are described. The author explains his rationale for choosing one modality over another and how newer imaging techniques will be used in the future.
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The bronchial a. are the nutrient vessels of the lung. Despite being high pressure (systemic) vessels they are of very small size compared to the pulmonary a. and their side branches are normally so minute that they are extremely difficult to visualize during in vivo studies--yet these branches also supply many important mediastinal structures including the esophagus, trachea, lymph nodes, pericardium, aorta, and mediastinal parietal pleura. The bronchial a. can react vigorously to pathological changes in the lung by hypertrophy and increased flow and their precise anatomy has become of increasing importance with the development of interventional techniques involving the systemic circulation of the lungs. In order to demonstrate the distribution and extent of these vessels we have adopted a casting technique using injections of various colors of latex to distinguish between pulmonary a. and veins, bronchial a. and veins and their connections with the pulmonary vascular bed in both normal and diseased lungs.
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A case of cavernomatous transformation of the portal vein demonstrated by magnetic resonance (MR) imaging is reported. Correlative images on scintigraphy and ultrasound are included. As in other vascular abnormalities, MR imaging is capable of depicting the findings noninvasively.
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The proton relaxation times of autopsy samples of arterial intima-media were measured with an NMR spectrometer and results correlated to the microscopically estimated lipid content of the vascular wall. The normal arterial intima-media contained two T1 relaxation components. The short T1 component (T1s) was 90 +/- 13 ms and its relative weight was 11%. The long T1 component (T1l) was 523 +/- 89 ms and relative weight 88%, respectively. The average T2 was 99 +/- 18 ms. In diseased vessels, a positive correlation was found between the lipid content of the vessel wall and the relaxation rate of the fast component. T1s of the intima-media was significantly shorter (P less than .01) in severe atheromatosis compared with vessels without fat deposition. The results suggest that atheromatous lesions should be best highlighted in spin-echo images by using short TR and TE to suppress the influence of T1l and to avoid (noncontrast contributing) T2 decay of the signal intensity.
Serial magnetic resonance imaging (MRI) and computed tomography (CT) were performed on a patient with metastatic lung cancer to brain. Magnetic resonance (MR) visualized two foci of intracerebral metastasis six weeks prior to CT.
Magnetic resonance (MR) imaging, the latest test for evaluation of patients with multiple sclerosis (MS), was assessed against clinical evidence in 74 patients with definite or probable MS. MR imaging was positive in 55 (85%) of 65 patients with definite MS but in only one (11%) of nine patients with probable MS. The examination is most likely to be positive when the patient is classified clinically as having definite MS; when the disease is active and not in remission; and if the constellation of symptoms indicates a multiplicity of regions with neurologic dysfunction. The examination was most sensitive for detecting lesions in the cerebral hemispheres, the posterior fossa, and the cervical spinal cord, in that order; it did not detect any lesions in the optic nerves. The paraclinical tests and MR imaging were of equal sensitivity in detecting MS lesions, but the latter method was more specific in localization. Cerebrospinal fluid evaluation was slightly less sensitive than the other two tests. There was no correlation between MR imaging and these examinations. The authors conclude that MR imaging is more sensitive than computed tomography (CT), which was positive in 25% of 59 patients with definite MS; it is always positive when CT is positive; and it probably can replace CT in the diagnosis and follow-up of patients with MS.
A low intensity artifact appearing at the junction of perirenal fat and renal parenchyma on MR images was recently described. A symmetrical high intensity artifact is also observable on the opposite side of the kidneys as well as at the junction of the right lobe of the liver and adjacent adipose tissue. Both artifacts can be explained as exhibitions of pixel misregistration due to the difference in chemical shifts of fatty and non-fatty organs. Identification of the chemical shift misregistration effect is important since the existence of this artifact may cause erroneous diagnosis of calcification and/or fluid collections.
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Conventional roentgenograms usually reveal a fatty tumor by its characteristic radiolucency. Exceptions to this presentation are the intrathoracic fatty tumors which are more often radiopaque than radiolucent. Obesity and steroids may cause focal, excessive accumulation of fat which can cause a mass effect and become symptomatic from pressure changes. Tubular widening of the superior mediastinum is characteristic mediastinal lipomatosis. Liposarcomas may or may not appear radiolucent. When a calcified retroperitoneal mass appears at least partially radiolucent, a liposarcoma must be suspected. Intrarenal fatty masses may be confused by overlapping bowel gas. Nephrotomograms, prior to the injection of contrast medium, will reveal the presence of fatty process. Obliteration of juxtavisceral or juxtamuscular fat is an important finding for localizing a disease process. CT is the most informative imaging method in establishing the presence of a fatty mass and for localizing a pathological process which infiltrates the juxtavisceral fat.
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Two cases of peripelvic hemorrhage simulating tumors (Antopol-Goldman lesion) are reported. In the 2 cases, nephrectomies were performed. With more knowledge of this lesion, and of its rapid disappearance, a waiting period and repeated intravenous pyelogram might prevent some unnecessary surgery.
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The author describes a new positioning device for use during radiography of the chest. This device is particularly helpful when doing a cardiac series.
Numerous noninvasive and invasive imaging modalities are available for the study of pancreatic disease. Disappointingly, the radiographic demonstration of a pancreatic neoplasm is more successful than the treatment of the disease. The proximity of large vascular structures to the pancreas makes its study technically difficult and explains why vascular invasion is readily caused by dispersion of pancreatic secretions (as seen in pancreatitis) or by neoplastic infiltration. The latter heralds nonresectability. Needle biopsy under fluoroscopic or echographic control appears to be gaining popularity as a simple, sensitive and specific method for establishing the diagnosis of pancreatic malignancy. Angiography has its highest yield in the diagnosis of islet cell tumors because they are generally hypervascular. This technique has been complemented by selective catheterization of pancreatic veins followed by hormone bioassay determinations.