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Biomedical subjects

J R Fike

Publications and source records attributed to J R Fike.

At least 55 records · Page 3Linked to original sources
PubMed1984

Dual energy CT scanning for analysis of brain damage due to X-irradiation.

Therapeutic irradiation is commonly used in the treatment of malignant brain tumors and has the potential to cause severe injury to normal tissues adjacent to a lesion. Computed tomography (CT) can be used not only to visualize tissue damage but to monitor the development of a lesion using advanced quantitative CT techniques. We have used a postprocessing dual energy CT method to quantify changes in tissue composition following large single doses of X-rays to the normal canine brain. The results suggest that these techniques will provide more information about the character of a lesion than is obtainable from conventional imaging procedures.

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PubMed1984

Contrast medium accumulation and washout in canine brain tumors and irradiated normal brain: a CT study of kinetics.

Kinetics of an iodinated contrast medium were evaluated quantitatively as a function of time up to one hour after intravenous infusion in the brains of dogs with experimentally induced radiation damage and dogs with spontaneous brain tumor. Radiation damage was characterized by an increase in iodine accumulation soon after the infusion, while tumor concentration of iodine either showed no change or decreased with time. These results suggest that contrast kinetic studies may be useful in differentiating radiation damage to normal brain tissue from a malignant brain tumor.

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PubMed1984

Computed tomography analysis of the canine brain: effects of hemibrain X irradiation.

Radiation damage induced by megavoltage X irradiation in normal brain tissue can manifest as one of several pathologic processes depending upon the time of brain examination after irradiation. Serial quantitative computed tomography (QCT) analyses were used to study the development of radiation damage in the normal canine brain. Tissue density, volume of low density areas, magnitude and volume of contrast uptake, and ventricular volume were measured following hemibrain irradiation and were correlated with histopathology. Low density areas correlated with edema, demyelination, axonal swelling, and necrosis and appeared 3-4 months after irradiation. Large regions of contrast enhancement (coagulation necrosis and associated vascular changes) appeared 5-6 months after irradiation. Results from this study demonstrated that the pathologic changes induced in the dog brain after single doses of X rays were similar to the changes observed in nonhuman primates and man after exposure to radiation.

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PubMed1983

X-ray computed tomography of brain tumors in cats.

X-ray computed tomography (CT) was used to depict intracranial space-occupying lesions in 5 cats. Computed tomographic findings were confirmed by surgical biopsy in 2 cases and at necropsy in 3 cases. The detailed anatomic information provided by CT scans facilitated surgical removal of a brain tumor in 2 cats, and allowed accurate tumor localization and dose optimization for radiation therapy in 1 cat. It was concluded that CT provides information required for accurate diagnosis and treatment of feline brain tumors.

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PubMed1983

Brain nuclear magnetic resonance imaging enhanced by a paramagnetic nitroxide contrast agent: preliminary report.

Contrast-enhancing agents for demonstrating abnormalities of the blood-brain barrier may extend the diagnostic utility of proton nuclear magnetic resonance (NMR) imaging. "TES," a nitroxide stable free radical derivative, was tested as a central nervous system contrast enhancer in dogs with experimentally induced unilateral cerebritis or radiation cerebral damage. After intravenous injection of TES, the normal brain showed no change in NMR appearance, but areas of disease demonstrated a dramatic increase (up to 45%) in spin-echo intensity and a decrease in T1 relaxation times. The areas of disease defined by TES enhancement were either not evident on the nonenhanced NMR images or were better defined after contrast administration. In-depth tests of toxicity, stability, and metabolism of this promising NMR contrast agent are now in progress.

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PubMed1982

Computed tomography of orbital tumors in the dog.

Computed tomography (CT) was used to investigate orbital tumors in 3 dogs. Tumors were clearly defined on transverse CT scans by their inherent density and gross distortion of normal orbital anatomy. Dorsal images synthesized from the original transverse scans were also used to visualize size and extent of tumors. Use of an iodinated contrast medium did not appear to improve localization of tumors in the orbit but was useful for identification of tumor extension into the calvaria. It was concluded that CT offered advantages over existing methods of radiographic diagnosis of orbital tumors and exophthalmos.

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PubMed1982

Quantitative evaluation of the canine brain using computed tomography.

Methods have been developed for the quantitative evaluation of the canine brain using computed tomography (CT). Sixteen studies in 10 adult Beagle dogs were used to define the precision for densitometry and dynamic studies in the normal canine brain. For various regions of the brain, intraanimal and interanimal variability was determined for normal tissue CT number, contrast enhancement, and parameters relating to blood flow and blood volume. High precision was obtained for densitometry both within and among animals when evaluated over a 9 month period. Both intra- and interanimal variability in dynamic measurements was relatively large between studies, but hemispheric comparisons within a given study and between studies showed high precision. These methods can be used to evaluate morphologic and physiologic changes in the canine brain following radiation or other cytotoxic treatments.

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PubMed1982

Radiation effects in the canine brain evaluated by quantitative computed tomography.

Quantitative computed tomography (QCT) and histopathology were used to assess the effects of large single doses of x irradiation on the normal canine brain. Measurable changes demonstrated by QCT included increased contrast enhancement and enlargement of the lateral ventricles, which were observed prior to any clinical signs. The results suggest that QCT methods are effective in the noninvasive evaluation of radiation-induced brain injury.

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PubMed1981

Computerized tomography of brain tumors of the rostral and middle fossas in the dog.

Computerized tomography (CT) was used to assess spontaneously occurring brain tumors of the rostral and middle fossas in the dog. Six dogs were used to illustrate the efficacy of CT as a noninvasive diagnostic procedure. Tumors were characterized on CT scans by density changes, presence of edema or calcification, displacement of normal anatomic landmarks, and contrast enhancement after injection of an iodinated contrast material. In terms of CT appearance, there were a number of morphologic similarities between human and canine brain tumors.

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PubMed1981

Anatomy of the beagle in cross-section: head and neck.

The transverse anatomy of the head and neck of the Beagle was studied. Cross-sectional preparations were photographed and compared with computerized tomographic scans, freshly prepared dissection specimens, and with skeletal preparations. Anatomic structures were identified by these means with the aid of anatomy texts. A series of labeled photographs were provided as a basis for interpretation of computerized tomography scans.

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PubMed1980

Canine anatomy as assessed by computerized tomography.

Computerized tomographic studies of normal canine anatomy were obtained, using a whole body scanner. The regions of interest were head and neck, thorax, and abdomen and pelvis. Scans were compared with gross transverse sections from one euthanatized dog. Identification and labeling of anatomic structures were aided by reference to recognized texts of canine anatomy.

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PubMed1979

Irradiation of the microvasculature with fast neutrons.

Single- and split-dose irradiation of the eyes of dogs was performed with cyclotron-produced polyenergetic neutrons at a rate of about 0.2 Gy (20 rad) per minute. Neovascularization was subsequently induced surgically in the avascular corneas and stimulated for 7 days to study the response of slowly proliferating capillary endothelial cells. Corneal tissue samples were evaluated quantitatively by morphometric methods. A dose-response curve was drawn by plotting per cent capillary volume versus dose. D0 was 2 Gy (200 rad), and the recovery ability was determined to be equivalent to 1.3 Gy (130 rad). Depending on the level of damage, relative biological effectiveness (RBE) values were 1.9 to 2.3.

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PubMedDate not supplied

Relative uptake of low- and high-osmolality contrast media in CT of brain tumors.

The magnitude and time course of contrast enhancement in spontaneous canine brain tumors was determined for two contrast agents: meglumine iothalamate and sodium meglumine ioxaglate. Tumor enhancement during contrast infusion and at 5, 10, 15, 30 and 45 minutes was measured using quantitative computed tomography. Blood iodine was measured using x-ray fluorescence. Peak contrast enhancement occurred during the infusion, and the magnitude was the same for both agents. Per gram of iodine infused, blood iodine was 12.4% higher with ioxaglate than iothalamate. The monoionic dimer ioxaglate is as effective as iothalamate for enhancement of canine brain tumors.

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PubMedDate not supplied

Comparative thermal dosimetry of interstitial microwave and radiofrequency-LCF hyperthermia.

Steady-state temperature distributions induced by commercial radiofrequency localized current field (RF-LCF) and microwave (MW) interstitial heating systems were compared in dog thigh muscle in vivo using repeated 15-min heating experiments in the same implant site. Control experiments consisting of up to nine successive, identical heat trials with either modality verified that induced temperature distributions could be duplicated reliably. For all comparative dosimetry experiments a square array of parallel heat sources and thermometry probes was inserted percutaneously through a 5 mm grid Plexiglas template to a depth of 7.0-8.0 cm. Metal trocar electrodes were left at the corners of square arrays for two or three successive RF-LCF heat trials. After the metal trocars were removed, two or three more heat trials were performed using dipole microwave antennas in Teflon catheters at the same four positions. The three-dimensional temperature distributions within the array boundaries were characterized by mapping up to 11 fibre optic temperature probes in 1 cm increments during the steady-state plateau of each trial. The distributions were analysed quantitatively in terms of the percentage of measured points which achieved at least 50 per cent of the maximum array temperature increase above baseline (delta Tmax). Results showed that the RF-LCF technique heated more uniformly with depth along the bare metal electrodes and more consistently within the array boundaries than the microwave dipole antennas. For all array spacings studied (1.0-3.5 cm), the RF electrodes heated approximately 10-20 per cent more of the array volume to greater than 50 per cent of delta Tmax.

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PubMedDate not supplied

Normal brain response after interstitial microwave hyperthermia.

The effects of interstitial hyperthermia were assessed in the normal brain after a single 30 min treatment using 2450 MHz microwaves. A single helical coil microwave antenna was inserted into the frontal white matter and reference temperatures of 40, 41, 42, 43 and 44 degrees C maintained for 30 min along a temperature sensing probe 5 mm away and parallel to the antenna. The extent of hyperthermia damage was quantified weekly for 6 weeks using computed tomography (CT), and changes in regional cerebral blood flow (rCBF), tissue vascularity and mean transit time were determined using ultrafast CT. Qualitative histopathological analysis was carried out on tissues at various times after heating. Heat lesions were radiographically characterized by rapid development and resolution and consisted of an area of focal low density surrounded by a ring of contrast enhancement. Histologically, the focus of low density corresponded to regions of tissue necrosis, whereas the ring enhancement showed local reactive changes, including endothelial cell proliferation and infiltration with macrophages. Tissue necrosis occurred at temperatures greater than 43.9 +/- 1.5 degrees C (mean +/- standard deviation), and volumes of necrosis and ring enhancement were at a maximum 1 week following treatment. Relative to the contralateral, unheated hemisphere, rCBF in the heated brain appeared to be reduced for the first 3 weeks after treatment but approached normal by week 4. The mean transit time of blood was increased for weeks 1-3 compared to the untreated hemisphere, and tissue vascularity reached a maximum, 3 weeks after treatment. The rapid CT changes together with ultrafast CT and histopathological findings suggest that focal heat lesions in the brain stimulate a significant and rapid vascular response.

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