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Biomedical subjects

L E Crooks

Publications and source records attributed to L E Crooks.

At least 91 records · Page 5Linked to original sources
PubMed1983

Nuclear magnetic resonance imaging clinical experience in San Francisco.

NMR is a new extremely promising imaging modality that combines the advantages of X-ray computed tomography by giving high resolution tomograms, of ultrasound by allowing imaging in any desired plane without the dangers from ionizing radiation and nuclear medicine by offering information about physiology and metabolic processes. These advantages are not combined with any of the drawbacks of the other modalities, and are due to the ability of NMR to provide information from four imaging parameters: 1) H density; 2) T1--the spin lattice relaxation parameters; 3) T2--the spin-spin relaxation parameter; and 4) information about proton motion. NMR is already a useful clinical tool in the study of brain, cord, mediastinum, pelvis, and is promising in the study of heart, kidneys, adrenals, liver, pancreas, and spleen.

Abdomen↗
PubMed1982

[Nuclear magnetic resonance imaging. Clinical applications].

Nuclear magnetic resonance (NMR) imaging is based on selective excitation of proton magnetic properties by means of a dual magnetic field. In the human body, NMR gives sectional images which represent hydrogen atom densities in the different tissues. The first results obtained in tomography of the brain, spinal cord, intrathoracic and abdominal organs and some vessels have been remarkable. The magnetic fields ans radiofrequency waves involved appear to be harmless. NMR imaging favourably compares with X-ray computerized tomography or with ultrasonography and will no doubt be increasingly used for its special qualities.

Abdomen↗
PubMed1982

Nuclear magnetic resonance imaging: current capabilities.

Nuclear magnetic resonance imaging can produce tomographic images of the body without ionizing radiation. Images of the head, chest, abdomen, pelvis and extremities have been obtained and normal structures and pathology have been identified. Soft tissue contrast with this method is superior to that with x-ray computerized tomography and its spatial resolution is approaching that of x-ray computerized tomography. In addition, nuclear magnetic resonance imaging enables us to image along the sagittal and coronal planes directly, and it does not produce obscuring artifacts by bone.

Humans↗
PubMed1980

In vivo imaging of the rat anatomy with nuclear magnetic resonance.

Live rats were imaged by nuclear magnetic resonance (NMR). These images demonstrated fine detail and high object contrast. Motion artifacts are not apparent in 4-minute images, and major blood vessels are demonstrated as regions of low signal intensity because of blood flow. Selective contrast enhancement is possible by varying NMR imager accumulation parameters.

Animals↗
PubMed1980

Tests for DNA and chromosomal damage induced by nuclear magnetic resonance imaging.

Chinese hamster ovary (CHO) cells in culture were exposed in a nuclear magnetic resonance (NMR) imaging apparatus to a strong magnetic field, pulsed field gradients, and radio frequency emissions. No chromosomal aberrations were induced even after an exposure of approximately 14 hours. No sister chromatid exchanges were induced by four-hour exposures to either low (average 7.2 mW) or high (average 61.2 mW) radio frequency power. When HeLa cells were exposed for 16 hours to an average radio frequency power of 61.2 mW, no inhibition of DNA synthesis was detectable. These data indicate that the conditions used for NMR imaging do not cause genetic damage which is detectable by any of these methods.

Animals↗
PubMedDate not supplied

Midgestational exposure of pregnant BALB/c mice to magnetic resonance imaging conditions.

The potential for producing reproductive toxicity or teratogenesis in mice by exposure to magnetic resonance imaging (MRI) conditions was evaluated by means of reproduction studies and the homeotic shift test. Embryos from pregnant BALB/c mice were exposed in vivo for 16 hours beginning on gestation day 8.75 to MRI conditions of modest field strength (static field, 0.35 tesla (T); pulsed gradients, 2.3 X 10(-4) T/cm for 2.5 to 10 msec; and radio frequency, 15 MHz at an average of 61.2 mW). Unexposed, sham-exposed (both MRI and X-ray) and X-irradiated (0.5 Gy) animals were the control groups. Neither placental resorptions nor stillbirths were increased by MRI. Fetal weight at birth and crown-rump length were proportional; however, crown-rump length was significantly less (p less than 0.001) in the MRI-exposed fetuses (respective mean values for MRI-exposed fetuses were 21.8 +/- 0.2 mm compared to 22.4 +/- 0.1 for sham-exposed fetuses). Both crown-rump length and fetal weight were significantly reduced after X-irradiation. The percentage of homeotic skeletal shifts was scored for each of eight anatomic sites. Only X-radiation produced significant increases in skeletal shifts. Prolonged midgestational exposure of mice to MRI conditions currently used for human clinical imaging, therefore, failed to reveal overt embryotoxicity (resorptions, stillbirths) or teratogenicity (homeotic shifts), consistent with the non-ionizing properties of MR. However, the slight but significant reduction in fetal crown-rump length after prolonged exposure justifies further study of higher MRI energy levels and consideration of other endpoints for establishing with greater confidence the safety of MRI during pregnancy.

Animals↗
PubMedDate not supplied

Tomographic imaging with nuclear magnetic resonance.

A technique is described for obtaining tomographic images of hydrogen distribution in animals using nuclear magnetic resonance (NMR). Resonant frequency is proportional to magnetic field strength, so that spatial resolution is achieved by frequency selection and magnetic field shaping. The results of scanning a phantom and two rats are presented.

Animals↗
PubMedDate not supplied

1981 Memorial Award Paper. Detectability of hepatomas in rat livers by nuclear magnetic resonance imaging.

NMR imaging of rats with implanted hepatomas in the liver demonstrates that under the imaging conditions of this study tumors of over 8 mm2 in area can be detected with high accuracy. Compared to normal liver, approximately 70% of these tumors had a combination of relaxation times (T1-T2) that could be uniquely identified as tumors, while the other 30% demonstrated relaxation time combinations that overlapped those previously found for abscesses, brain, and hematomas.

Animals↗
PubMedDate not supplied

Proton nuclear magnetic resonance imaging of acute experimental cerebral ischemia.

To determine the efficacy of proton nuclear magnetic resonance (NMR) imaging in documenting acute ischemic infarction and to characterize the changes in these images during the first 24 hours following the ischemic insult, serial NMR imaging was performed in gerbils that had undergone unilateral carotid artery ligation. No significant changes in the signal intensity, T1 or T2 relaxation times were noted for either asymptomatic animals or the control hemisphere of symptomatic gerbils. There was a significant increase in T1 and especially T2 relaxation times and in both the relative signal intensity and Hf(v) for the ischemic hemisphere of symptomatic gerbils. These parameters appeared to increase linearly over 24 hours. The ischemic lesion first could be detected by NMR as early as 3 hours after carotid artery ligation, our earliest time point. The physiologic significance of these changes is discussed. These data suggest that NMR imaging may have significant diagnostic importance for acute cerebral ischemia and infarction in man.

Acute Disease↗
PubMedDate not supplied

Temperature distribution measurements in two-dimensional NMR imaging.

This paper represents a preliminary study of the effects of regional temperature distribution in two-dimensional nuclear magnetic resonance (NMR) T1 imaging. It is found, as expected, that variations in local temperature appear as variations in the corresponding T1 image. The potential use of NMR T1 imaging in temperature measurements is evaluated in the case of water and blood samples. Using containers where the temperature could be either known or directly controlled with reasonable accuracy, images are obtained with samples having at least two regions at different temperatures. As expected, T1 is found to vary linearly with 1/T over the range of 0 degrees C to about 40 degrees C for blood. The potential use of T1 imaging in hyperthermia applications is also discussed.

Blood↗
PubMedDate not supplied

MR imaging of aortoiliac atherosclerosis with 3D image reconstruction.

A computer program was written to detect blood flow in a sequence of magnetic resonance images, using reduction in first echo intensity and prolongation of calculated T2 value, and to construct three-dimensional vessel maps from the detected flow regions. Reconstructed vessel images were coded to show cross-sectional area of the lumen and relative flow velocity along the length of the vessel. The program was applied to imaging the aorta and iliac arteries in 11 patients with atherosclerosis and results were compared with angiography. All sites of narrowing were identified by the algorithm, but no flow at all was detected at one site of partial occlusion.

Aortic Diseases↗
PubMedDate not supplied

Nuclear magnetic resonance imaging of syringomyelia.

Five patients with syringomyelia were examined with a 3.5 kG nuclear magnetic resonance (NMR) imager. Syrinx cavities were visualized in all five cases, and image quality compared favorably with metrizamide computed tomography (CT). Axial images were optimal for identifying syrinx cavities, and sagittal views were useful in providing an overview of cord morphology and in examining the craniocervical junction. Inversion-recovery images were less valuable than the spin-echo sequences. By varying spin-echo imaging parameters, tissue relaxation times could be determined and the fluid nature of the syrinx cavities confirmed. This limited study suggests that NMR may challenge the current role of CT in the diagnostic workup of syringomyelia.

Diagnosis, Differential↗
PubMedDate not supplied

NMR in experimental cerebral edema: value of T1 and T2 calculations.

In an experimental investigation, the efficacy of nuclear magnetic resonance (NMR) relaxation times in measuring brain water was studied. Cerebral edema was induced in four dogs with a freeze lesion, which was produced by contact with a steel cylinder cooled in liquid nitrogen and placed on the exposed dural surface of the brain. NMR proton imaging was performed 2, 3, 6, or 24 hr after production of the lesion, at a field strength of 0.35 T, using multiparametric spin-echo (SE) technique. The animals were sacrificed immediately after imaging, and brain samples were analyzed for water content (wet-to-dry, microgravimetry). Correlation between water content, NMR imaging, and resulting T1, T2 relaxation times and mobile proton density values calculated with SE technique was performed. Brain sample analysis showed elevation of water content in the white matter subjacent to the lesion in all four dogs, rising at least 15% in each of the animals. NMR imaging detected the freeze lesion and subjacent vasogenic edema of the white matter in all animals. The 2 sec pulse interval SE technique was most sensitive in the detection of the abnormality, and provided optimal differentiation of gray and white matter. The second echo sampling (56 msec) was most sensitive to the detection of edema. The T1 and T2 relaxation values, as well as the mobile proton density values, were elevated in the normal gray matter and in the abnormal white matter when compared with normal white matter in any given animal.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗