Toshifumi Kamiryo

Histological changes in the normal rat brain after gamma irradiation

SummaryRadiation-induced changes in the parietal cortex of Wistar rats were observed at various time points after gamma surgery. Maximum dosages of 50, 75, and 120 Gy were given at the iso-center of the radiation using a 4-mm collimator. Conventional histochemical and immunocytochemical analyses, and computer-assisted videomicroscopy were utilized to examine perfusion-fixed brain tissue.Irradiation at a dosage of 50 Gy elicited morphological changes of astrocytes in the parietal cortex at 3 months. Vasodilatation became obvious at 12 months; fibrin deposition was observed in the dilated capillary wall. Neither leakage of Evans Blue from the vasculature into the tissue nor necrosis was observed across the 12 month observation period.Irradiation at a dosage of 75 Gy resulted in morphological changes of astrocytes within 1 month. Dilatation of vessels and capillary thickening were observed at 3 months. Evans Blue leakage and necrosis were observed at 4 months after 75 Gy irradiation. At this time, the walls of arterioles became thickened by subintimal accumulation of fibrin and hyaline substance; this sometimes resulted in occlusion of the lumen. Significant hemispheric swelling was observed at 4 months.Irradiation at a dosage of 120 Gy elicited changes in astrocytic morphology within 3 days. Evans Blue leakage into the tissue was observed by 3 weeks. Vasodilatation became marked at this time point and rarefaction was observed in the irradiated cortex. Necrosis was observed at 4 weeks, however, no significant swelling was observed.Taken together, these findings demonstrate time-dependent and dosage-dependent changes in normal cerebral tissue after Gamma Knife irradiation. These results provide a basis for gauging the impact of gamma surgery in regions of eloquent tissue. An enhanced understanding of the cellular responses to radiosurgery will contribute to developing and evaluating future applications for gamma surgery.

Radiosurgery-induced microvascular alterations precede necrosis of the brain neuropil

OBJECTIVERadiosurgery is used as a therapeutic modality for a wide range of cerebral disorders. It is important to understand the underlying causes of deleterious side effects that may accompany gamma-irradiation of brain tissue. In this study, structural alterations in rat cerebral vessels subjected to gamma knife irradiation in vivo were examined, for elucidation of their potential role in necrosis formation. METHODSA maximal center dose of 75 Gy was delivered to the rat parietal cortex with a 4-mm collimator, and changes occurring before necrosis formation were assessed 3.5 months after irradiation. Transmission electron microscopy, using horseradish peroxidase as a tracer, and scanning electron microscopy with vascular casting were performed. RESULTSThe capillary network in the irradiated area exhibited thickening and vacuolation of the basement membrane. The capillary density in the irradiated area was lower and the average capillary diameter was larger, compared with the nonirradiated side. These results indicate that substantial changes in the neuropil do not occur 2 weeks before the time of definite necrosis formation, whereas changes in the basement membrane are prominent. CONCLUSIONThe necrotic response to intermediate doses of focused-beam irradiation appears after a considerable latency period and then progresses rapidly. This contrasts with previously reported responses to fractionated whole-brain irradiation, in which damage occurs slowly and gradually. Alterations in the microvascular basement membrane precede overt cellular changes in neuronal and vascular cells and provide an early index of cerebrovascular dysfunction in regions destined to undergo necrosis.

Occlusion of the anterior cerebral artery after gamma knife irradiation in a rat

SummaryThe anterior cerebral artery of rats was irradiated at the level of the circle of Willis by Gamma Knife with a maximum dose of 25, 50, or 100 Gy. Occlusion of the anterior cerebral artery was observed in one rat which was followed for 20 months after irradiation of 100 Gy. Cerebral infarction was found at the midline-frontal region and the cingulate gyrus. Arterial wall thickening with fibrosis, splitting of the internal elastic membrane, luminal organized thrombus, and migration of smooth muscle cells into the thrombus were observed. In the anterior cerebral artery, thrombus formation seemed to occur after the endothelial injury and this may play a prominent role for occlusion. In small arteries, various changes were observed in the irradiated tissue. These included fibrosis and thrombus, thickened smooth muscle layer, lymphocytic infiltration, and thickening of vessel wall with fibrosis and fibrinous thrombosis with leakage of fibrin into the surrounding tissue after different doses of radiation and at different observation times. These changes were comparable to the ordinary vascular response to injury including healing vasculitis and arteriosclerosis.

Enhanced magnetic resonance imaging of the rat brain using a stereotaetic device with a small head coil: Technical note

SummaryA stereotactic device (SDM) was developed for performing consistent magnetic resonance imaging (MRI) of the rat brain. The SDM was developed by adapting a radiofrequency transmit/receive head coil of 4.4 cm inner diameter (quadrature birdcage head coil), and utilizing partial acrylic construction for the positioning elements. The small head coil provides improved resolution and accuracy of the image, while the stereotactic holder permits repeatable and accurate imaging of identified brain structures.This system provides several advantages over existing experimental MRI devices. The SDM ensures that the head is always placed in the center of the coil in a uniform fashion. Standardized positioning of the skull optimizes image quality and provides a consistent orientation of the brain. In addition, a widely-utilized coordinate system described by Paxinos and Watson can be employed to assist in the identification of structures and to facilitate surgical planning.The SDM is compatible with a recently-developed stereotactic device for radiosurgery with the Gamma Knife, thus permitting the planning and performance of experimental radiosurgery using the same coordinate system. The SDM also provides the ability to perform MRI and radiosurgery at different times, thus avoiding the need for prolonged anesthesia during an experimental study. Finally, the SDM allows repeated MRI of the same, identifiable positions in the brain during longitudinal experimental studies. The utility of this device is demonstrated here by examining the time course of cerebral damage that evolved within a radiosurgical focus after gamma irradiation.

Gamma knife irradition—Induced changes in the normal rat brain studied with 1H magnetic resonance spectroscopy and imaging

Rationale and Objectives. The pathogenesis of brain injury following radiosurgery is poorly understood. To better elucidate the relationship between blood—brain barrier disruption and metabolic derangements, we used magnetic resonance (MR) imaging and 1 H MR spectroscopy to detect early changes from focused single-fraction, high-dose irradiation injury in rat brains. Methods. Using the Leksell gamma knife, we irradiated the frontoparietal cortex of 11 male Wistar rats with a single dose of 120 Gy. Four weeks later, we sequentially performed water-suppressed 1 H MR spectroscopy and gadopentetate dimeglumine—enhanced T1-weighted MR imaging. Metabolic maps were created of n -acetylaspartate (NAA), creatine and choline (Cr/Cho), and lactate from the MR spectroscopy data set. Detection of irradiation injury among the tested modalities was assessed by receiver operating characteristic analysis and by quantitative signal intensity changes. Pathologic confirmation of irradiation damage was obtained in all rats. Results. Gadopentetate dimeglumine—enhanced T1-weighted MR imaging was the only imaging modality that detected statistically significant signal intensity changes ( p 1H MR spectroscopy. Conclusion. In our animal model, blood—brain barrier disruption was a reproducible, integral finding of single-fraction, high-dose irradiation injury. No reproducible metabolic derangements of ischemia or necrosis were detected by 1 H MR spectroscopy, possibly because of dose—latency effects or sensitivity issues.

A stereotactic device for experimental gamma knife radiosurgery in rats. A technical note.

SummaryA rat stereotactic device was designed for use in Gamma Knife radiosurgery. Experimental radiosurgical lesions were made in superficial and deep cerebral structures to verify the accuracy of the coordinate system, which is based on a standard rat stereotactic atlas. Calculated dosages were shown to be accurate utilizing thermoluminescence dosimetry. Two additional features of the device permit the surgical positioning and placement of electrodes, and postmortem slicing of the brain according to the same coordinate system. This new apparatus allows precise and repeatable gamma irradiation of the rat brain without the need for expensive and time-consuming imaging techniques. Studies of this type will provide a rapid means for examining the effects of radiosurgery on the central nervous system.

Accuracy of an experimental stereotactic system for MRI-based gamma knife irradiation in the rat

SummaryStereotactic devices for experimental Gamma Knife irradiation and magnetic resonance imaging (MRI) have recently been developed for experimental studies using rats [6, 7]. The present study examined the accuracy of these devices using the following two approaches. In the first approach, Gamma Knife irradiation was performed using the stereotactic device with targets based on a standard stereotactic atlas. Gadolinium-enhanced T1-weighted magnetic resonance imaging was performed using the MRI stereotactic device. Animals were then sacrificed after Evans blue injection, and the rat brain was sliced using an attachment to the stereotactic device. The center coordinates of the gadolinium-enhanced area from the MRI and Evans blue-stained area from the tissue sections were obtained using a computer-assisted image analysis system. These coordinates were compared with the target coordinates planned from the stereotactic atlas. In the second approach, a thermoluminescence dosimeter was implanted in the rat brain. Stereotactic MRI was performed using the stereotactic MRI device, and the coordinates of the implant were obtained. Gamma Knife irradiation was then performed at this target using the stereotactic device. The absorbed dose was measured and compared with the planning dose.These experiments demonstrated a spatial error of 0.6 mm (standard error ± 0.07) between Gamma Knife irradiation based on a comparison of the atlas coordinates and the lesion, and a spatial error of 1.0 mm (standard error ± 0.13) based on a comparison of the stereotactic MR images and the lesion. Gamma Knife irradiation based on MR images using the stereotactic device demonstrated a maximum error of 10% in absorbed dose at the target center. Together, the stereotactic devices for Gamma Knife irradiation and magnetic resonance imaging provide useful tools for Gamma Knife research in an animal model.

Stereotactic frame-based error in magnetic-resonance-guided stereotactic procedures : A method for measurement of error and standardization of technique

When using the stereotactic Leksell G frame for magnetic-resonance-based functional stereotactic lesions, the authors occasionally encountered a situation in which it was not possible to apply the anterior plate of the coordinate box successfully because it came into contact with the anterior posts of the frame; it was noted that the posts as well as the base ring became distorted by the force required to insert the cranial fixation pins. To examine this issue, measurements were taken of the amount of distortion relative to the torque on the screws. It was also found that backward movement of the posterior segment of the base ring indirectly narrowed the anterior spaces for plate insertion. A determination was made that torque over 6 inch pounds caused undesirable contact between the posts and the coordinate box.

Stereotactic laser-guided approach to distal middle cerebral artery aneurysms.

SummaryThe Steiner-Lindquist laser intra-operative guidance method is described and its application in the surgical treatment of mycotic aneurysm is presented. Three illustrative cases of distal middle cerebral artery aneurysms are reported. The authors argue that all ruptured mycotic aneurysms should be treated surgically. The laserguided stereotactic approach is presented as simple, flexible and reliable method to improve safety and accuracy of the operation in these cases. In our experience it compares favorably with previously described stereotactic techniques.

The Baromodulatory Effect of Gamma Knife Irradiation of the Hypothalamus in the Obese Zucker Rat

Objective: The aim of this study was to evaluate the effect on body weight set point over time of focused, subnecrotic doses of radiation via gamma knife (GK) to the hypothalamus of the genetically obese Zucker rat. Methods: A total of 36 adolescent animals were used in this experiment and placed in 6 groups of 6. The genetically obese homozygous Zucker rat was used in 4 groups (n = 24) and received GK, subcutaneous cobalt protoporphyrin (CoPP), both treatments combined or sham treatment. The heterozygous lean Zucker rat was used in 2 control groups (n = 12) and received either GK or sham treatment. All animals were weighed at the beginning of the experiment and at weekly intervals for 34 weeks. GK irradiation was accomplished using a specially designed stereotactic frame and a total dose of 40 Gy was given to 2 nearby targets in the medial hypothalamus. The drug subgroups received weekly subcutaneous injections. All animals were housed in the same environment with unlimited access to food. Results: There were no significant differences in weight between the lean GK and sham groups. For the obese cohort, beginning at week 7 and throughout the remainder of the experiment, there were significant and sustained reductions in weight set point for animals that received GK (p < 0.05) and CoPP (p < 0.05) compared to sham-treated animals. Curiously, there was no statistical difference between the combined treatment and sham subgroups, though there was a trend toward weight reduction (p < 0.10). With the exception of one animal in the obese GK cohort in which there was a small area of necrosis lateral to the target area, histopathological analysis failed to reveal any abnormalities. There were no gross behavioral abnormalities noted. Conclusion: Our experimental results suggest that a single dose of GK irradiation to the hypothalamus can produce sustained reduction in the weight set point without emaciation in adolescent animals. The effect of this treatment is comparable to a well-studied drug therapy with a metalloporphyrin. We hypothesize that this involves a resetting of the hypothalamic set point for body weight through an as yet uncharacterized neuromodulatory effect.