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Pulsed radiofrequency (PRF) fields applied by an electrode to neural structures, such as the peripheral sensory nociceptor axons and dorsal root ganglion, are clinically effective in reducing pain and other neuropathic syndromes. However, a full understanding of the underlying mechanisms by which this occurs has not yet been clarified. In this study, PRF is applied to the afferent axons of the sciatic nerves of rats. A standard radiofrequency (RF) electrode and RF generator is used to apply the RF signal output to the sciatic nerve using standard PRF parameters that have been successfully used in clinical practice. The ultrastructure of the treated axons is observed after 10 days by electron microscopy. A control, sham application is simultaneously applied to the contralateral sciatic nerve to provide a statistical differential comparison. It is found that the internal ultrastructural components of the axons show microscopic damage after PRF exposure, including: abnormal membranes and morphology of mitochondria, and disruption and disorganization of microfilaments and microtubules. The damage appears to be more pronounced for C-fibers than for A-delta and A-beta fibers. The results are discussed in terms of internal electric field strengths and thermodynamic parameters.

This study aims to compare radiofrequency (RF) heat lesion size across electrodes and generator settings available for interventional pain management.Monopolar lesions are generated ex vivo in animal tissue using sharp cannulae with tip diameters 23, 22, 20, 18, 16 gauge; tip lengths 5, 6, 10, 15 mm; set temperatures 60, 70, 80, 90°C; set times 1, 1.5, 2, 3, 5, 10 minutes. Lesions are generated using the RRE electrode, cooled RF, and parallel-tip bipolar RF for comparison. Lesion sizes are assessed by automated photographic temperature inference from over 400 lesions, using multiple lesions per configuration.Monopolar lesion width and length increase with each factor (P 0.001). Increasing cannula diameter from 22 to 16 gauge increases average lesion width 58-65% (3-4 mm) at 80°C and 2 minutes. Increasing temperature from 60°C to 90°C increases lesion width 108-152% at 2 minutes. Although dimensions grow most rapidly over the first minute, average lesion width is 11-20% larger at 2 minutes, and 23-32% larger at 3 minutes, compared with 1 minute. Lesion length extends distal and proximal to the tip, and exceeds tip length by 1-5 mm at 80°C and 2 minutes. Conventional 16 gauge cannulae at 80-90°C for 2-3 minutes generate lesions of average width similar to that produced by the cooled RF configuration proposed for sacroiliac joint denervation. Bipolar RF between parallel cannulae produces a rounded brick-shaped lesion of comparable shape to three sequential monopolar lesions generated using the same cannulae and generator settings.Tip gauge, tip length, temperature, and time substantially affect RF lesion size.

Ex vivo photographic temperature mapping of bipolar radiofrequency (RF) lesions in animal tissue is performed over a wide range of electrode tip spacings, tip lengths, tip diameters, tip temperatures, and lesion times. In vivo temperature measurements collected during clinical treatment of sacroiliac joint (SIJ) pain corroborate those collected ex vivo. Generation of a "strip lesion" connecting two separated bipolar electrode tips is demonstrated ex vivo for tip spacings as large as 20 mm. A rounded rectangular bipolar lesion with midline dimensions 12 mm × 15 mm × 8 mm (L × W × D) is demonstrated using 10 mm parallel tip spacing, 10 mm tip lengths, 20 gauge cannulae, 90°C tip temperature, and 3-minute lesion time. Lesion length can be increased to 18 mm by using 15 mm tip lengths. Lesion width can be increased to 17 mm by using 12 mm tip spacing. The size of conventional bipolar lesions can exceed the size of lesions produced both by conventional monopolar RF (12 mm × 7 mm × 7 mm ellipsoidal) and by cooled monopolar RF as used in spinal pain management (10 mm × 10 mm × 10 mm spherical). SIJ pain is treated by placing 5 to 7 straight RF cannulae perpendicular to the dorsal sacrum and producing 4 to 6 overlapping bipolar RF lesions between the dorsal sacral foramina and the ipsilateral SIJ. This bipolar "palisade" (a defensive fence) creates a continuous lesion spanning the region through which multiple sacral lateral branch nerves travel along irregular, branching paths to reach the SIJ.

Cambridge, Massachusetts, USA Abstract Objective. A study is carried out of the spatial distribution and time dependence of electric and thermal fields in the tissue around a radiofrequency (RF) electrode used in pain therapy. Finite- element calculation of the fields is performed, and results are compared with ex vivo tissue data. Field predictions are made for continuous and for pulsed RF applications. Design. A special RF cannula electrode is constructed with both macro and micro thermocouple sensors to measure both average and rapid, transitory temperature effects. Temperatures and impedances are recorded in liver and egg-white models using signal outputs from a commercially available RF lesion generator. These data are compared with the results of finite-element calcula- tions using electric field equations and the bio-heat equation. Results. Average and pulsatory temperatures at the RF electrode are measured. Rapid temperature spikes during pulsed RF bursts are observed. These data compared well with theoretical calculations using known electrical and thermal tissue parameters. Conclusion. Continuous RF lesioning causes heat destruction of neurons. Pulsed RF lesioning (PRFL) produces heat bursts with temperatures in the range associated with destructive heat lesions. PRFL also produces very high electric fields that may be capable of disrupting neuronal membranes and function. Finite-element calculations agree substantially with the measured data, giving con- fidence to their predictions of fields around the RF electrode.

The techniques and results of the main percutaneous procedures performed using image guidance with computerized tomography, including cordotomy, trigeminal tractotomy-nucleotomy, and extralemniscal myelotomy, are presented. The advantages of image guidance for anatomical orientation during the procedures and the newly designed radiofrequency needle-electrode systems are stressed.

To evaluate whether coagulation necrosis achievable with radio-frequency (RF) ablation can be increased by using a cluster of closely spaced electrodes.RF was applied to ex vivo liver (n = 68), in vivo liver (n = 12), and in vivo muscle (n = 15) by using a cluster array of three separate internally cooled electrodes spaced 0.5 cm apart. The diameter of coagulation necrosis achieved with optimal RF deposition (1,400-2,150 peak mA) for 5-60 minutes of RF application was determined for electrode tip lengths of 1.5-3.0 cm and compared with that obtained by using a single electrode and otherwise similar technique. Ten patients with solitary intrahepatic colorectal metastases were also treated by using cluster electrode RF ablation.In ex vivo liver, simultaneous RF application to electrode clusters for 15, 30, and 45 minutes produced 4.7 cm +/- 0.1, 6.2 cm +/- 0.1, and 7.0 cm +/- 0.2 of coagulation necrosis, respectively. In in vivo liver and muscle, RF applied to electrode clusters for 12 minutes yielded 3.1 cm +/- 0.2 and 7.6 cm +/- 0.4 of coagulation, respectively. RF application to a single electrode produced maximal coagulation of 2.9 cm in ex vivo liver, 1.8 cm in in vivo liver, and 4.3 cm in muscle (P.01, all tissues). In colorectal metastases, a single 12-15-minute application of RF to an electrode cluster induced 4.5-7.0 cm of coagulation necrosis.Simultaneous RF application to a cluster of three closely spaced internally cooled electrodes enables a larger volume of coagulation in ex vivo liver, in vivo tissues, and hepatic colorectal metastases than previously reported.

We present a new radiofrequency needle electrode system for use in pain-relieving procedures. The electrode system is used for computed tomography-guided percutaneous cordotomy, extralemniscal myelotomy, and trigeminal tractotomy. These special electrodes make it possible to perform selective cordotomies and selective trigeminal tractotomies under direct computed tomographic image control.

Ex vivo photographic temperature mapping of bipolar radiofrequency (RF) lesions in animal tissue is performed over a wide range of electrode tip spacings, tip lengths, tip diameters, tip temperatures, and lesion times. In vivo temperature measurements collected during clinical treatment of sacroiliac joint (SIJ) pain corroborate those collected ex vivo. Generation of a "strip lesion" connecting two separated bipolar electrode tips is demonstrated ex vivo for tip spacings as large as 20 mm. A rounded rectangular bipolar lesion with midline dimensions 12 mm × 15 mm × 8 mm (L × W × D) is demonstrated using 10 mm parallel tip spacing, 10 mm tip lengths, 20 gauge cannulae, 90°C tip temperature, and 3-minute lesion time. Lesion length can be increased to 18 mm by using 15 mm tip lengths. Lesion width can be increased to 17 mm by using 12 mm tip spacing. The size of conventional bipolar lesions can exceed the size of lesions produced both by conventional monopolar RF (12 mm × 7 mm × 7 mm ellipsoidal) and by cooled monopolar RF as used in spinal pain management (10 mm × 10 mm × 10 mm spherical). SIJ pain is treated by placing 5 to 7 straight RF cannulae perpendicular to the dorsal sacrum and producing 4 to 6 overlapping bipolar RF lesions between the dorsal sacral foramina and the ipsilateral SIJ. This bipolar "palisade" (a defensive fence) creates a continuous lesion spanning the region through which multiple sacral lateral branch nerves travel along irregular, branching paths to reach the SIJ.

Using a chronically implanted telemetric pressure sensor, we have determined the quantitative relationship between changes in body position and ventricular fluid pressure in normal subjects and subjects with shunts. The method allows accurate, reliable measurement of negative as well as positive pressures. We describe the derangement of postural intraventricular pressure regulation caused by placement of a shunt, as well as the influence of various shunt systems and the antisiphon device on this problem. Ventriculoatrial, ventriculoperitoneal, and ventriculopleural shunts all caused similar severely abnormal postural intracranial pressure relationships. The antisiphon device was generally effective in restoring normal pressures in patients in the upright position. We discuss the implications of our findings for understanding the mechanisms of postural intracranial pressure regulation in patients without hydrocephalus.

A hierarchical model based on the Multivariate Autoregessive (MAR) process is proposed to jointly model neurological time-series collected from multiple subjects, and to characterize the distribution of MAR coefficients across the population from which those subjects were drawn. Thus, inference about effective connectivity between brain regions may be generalized beyond those subjects studied. The posterior on population- and subject-level connectivity parameters are estimated in a Variational Bayesian (VB) framework, and structural model parameters are chosen by the corresponding evidence criteria. The significance of resulting connectivity statistics are evaluated by permutation-based approximations to the null distribution. The method is demonstrated on simulated data and on actual multi-subject neurological time-series.

The key challenge facing the neurosurgeon during neurosurgery is to be able to remove from the brain as much tumor tissue as possible while preserving healthy tissue and minimizing the disruption of critical anatomical structures. The purpose of this work was to demonstrate the use of biomechanical simulation of brain deformation to project preoperative fMRI and DTI data into the coordinate system of the patient brain deformed during neurosurgery. This projection enhances the visualization of relevant critical structures available to the neurosurgeon. Our approach to tracking brain changes during neurosurgery has been previously described. We applied this procedure to warp preoperative fMRI and DTI to match intraoperative MRI. We constructed visualizations of preoperative fMRI and DTI, and intraoperative MRI showing a close correspondence between the matched data. We have previously demonstrated our biomechanical simulation of brain deformation can be executed entirely during neurosurgery. We previously used a generic atlas as a substitute for patient specific data. Here we report the successful alignment of patient-specific DTI and fMRI preoperative data into the intraoperative configuration of the patient's brain. This can significantly enhance the information available to the neurosurgeon.

A system has been devised to focus a video camera mounted on a CRW stereotactic frame onto the surgical field and to integrate the video picture with a computer-generated three-dimensional view of structures or targets deep within the brain. The surgical resection can then be done with the surgeon looking either at the composite picture on the video/computer monitor (as in almost all endoscopic surgery) or at the surgical field, to perform the resection using the conventional techniques most comfortable to the surgeon and most effective for the resection. The graphics platform on which the Exoscope program is built is the same as used for the RSA X-Knife stereotactic radiosurgery system. The X-Knife graphics program allows the reconstruction of a target mass (such as intracranial tumor) and desired objects (such as surrounding vessels) with accurate registration to stereotactic coordinates derived from the CRW localizing system. By mounting a video system through an externally mounted endoscope on the CRW arc, it is possible to orient the video image with great accuracy to this same stereotactic space. The two images are superimposed on a computer/video console in the operating room. The surgeon visualizes a real-time video image of the operating field upon which is a graphical representation of the computer-generated image of the target mass beneath the surface. In the corners are triplane orthogonal views through the center of target and a view parallel to the trajectory, so the surgeon may gauge his or her progress toward the target.(ABSTRACT TRUNCATED AT 250 WORDS)

Purpose: A new method for stereotactic irradiation of spinal malignancies is presented, with evaluations of the theoretic and practical limitations of localization accuracy and the implementation of the method in swine. Methods and Materials: In a percutaneous procedure, a minimum of three small (1.7-mm-diameter) titanium markers are permanently affixed to a vertebra. Markers are localized on biplanar radiographs while isocenter positions are determined on CT. An external fiducial frame defines a three-dimensional coordinate system through the patient. Radiographs coupled with a rigid body rotation algorithm account for daily differences in patient position. Phantom studies were used to verify theoretic uncertainty calculations from a simulation program. A swine model was used to evaluate the difficulty and duration of the implant technique, the suitability of the vertebral process as an implant site, vertebral motion due to normal respiration, and the ability to target one vertebra with markers in an adjacent vertebra. Results: Theoretic accuracy studies confirmed that localization accuracy is a function of marker separation. Phantom studies involving 296 measurements showed that individual implants could be localized within 0.25 mm. The largest targeting error observed in 3,600 measurements of 100 implant configurations was 1.17 mm. The implant procedure took 5‐10 minutes per site. No significant migration of implants was observed up to 35 days postimplantation, and respiratory motion had no detectable influence on vertebral position. Adjacent vertebrae may be useful for targeting one another with a small sacrifice in localization accuracy. Conclusions: The use of implanted markers for localization of spinal malignancies has potential for applications in stereotactic radiotherapy. Phantom measurements suggest that localization accuracy similar to intracranial stereotactic radiotherapy techniques is achievable. Swine studies suggest that the implant technique is expedient and feasible for tumor targeting purposes. © 2002 Elsevier Science Inc.

OBJECTIVE: Application of pulsed radiofrequency (RF) currents to the dorsal ganglion has been reported to produce long-term relief of spinal pain without causing thermal ablation. The present study was undertaken to identify spinal cord neurons activated by exposure of the dorsal ganglion to pulsed RF currents in rats. METHODS: Left-sided hemilaminectomy was performed in adult Sprague-Dawley rats to expose the C6 dorsal root ganglion. An RF electrode (0.5 mm diameter) with a thermocouple for temperature monitoring was positioned on the exposed ganglion, and rats were assigned to one of three treatment groups: pulsed RF treatment (20 ms of 500-kHz RF pulses delivered at a rate of 2 Hz for 120 s to produce tissue heated to 38°C), continuous RF (continuous RF currents for 120 s to produce tissue heated to 38°C), or sham treatment (no RF current; electrode maintained in contact with ganglion for 120 s). RESULTS: Treatment with pulsed RF but not continuous RF was associated with a significant increase in the number of cFOS-immunoreactive neurons in the superficial laminae of the dorsal horn as observed 3 hours after treatment. CONCLUSION: Exposure of the dorsal ganglion to pulsed RF currents activates pain-processing neurons in the dorsal horn. This effect is not mediated by tissue heating.

Publisher Summary This chapter focuses on computer-assisted technologies for neurosurgical procedures. The high-speed, modern computer is revolutionizing almost every area of modern science and technology. Its use in the computerized tomographic scan (CT scan) produced an astonishing quantum jump in medicine, essentially ushering in a new era in radiology and surgery. Computer tomographic scans can be created today by several types of imaging modalities. These include X-ray scans, magnetic resonance image (MRI) scans, and positron emission tomographic (PET) scans. For the first time, with the use of computer technology, one has a noninvasive anatomical slice through the most exquisite portions of the body. Such pictures are both beautiful and practical. For the diagnostic neuroradiologist, this window into the brain is a powerful tool for the detection of disease as manifested by aberrant morphological status or unusual tissue properties. The visualization of brain tumors and other brain pathology became immediately evident. Qualitative radiology was, however, only the beginning of the impact of the CT scan revolution. Next came the progress in spatial quantification of the images and attachment of coordinate reference frames to the data. This led to stereotactic image-guided neurosurgery, and stereotactic radiosurgery and radiotherapy of the brain, which have been at the forefront of the neurosurgical field for the past decade.

New radiofrequency lesion dorsal root entry zone (DREZ) electrodes for relief of facial pain were designed based on a neuroanatomic study in man of the trigeminal nucleus caudalis at the cervicomedullary junction. The human brainstems of 3 normal postmortem specimens were sectioned with measurements and relationships of the trigeminal nucleus caudalis, segmental tracts, spinocerebellar tracts and dorsal columns. Two right-angle DREZ electrodes were made by Radionics for producing DREZ lesions in the trigeminal nucleus caudalis to treat deafferentation facial pain.

The mass and energy distributions for fusion products corresponding to 128.9 MeV $^{32}\mathrm{S}$ on $^{12}\mathrm{C}$, $^{25}\mathrm{Mg}$, and $^{40}\mathrm{Ca}$ targets has been measured at 8\ifmmode^\circ\else\textdegree\fi{} lab using a time-of-flight spectrometer. The heaviest product observed with significant cross section for each system has a mass five units less than that of the corresponding compound system. Lighter dominant mass groups are separated by approximately three mass units. Such mass systematics can be understood in terms of neutron, proton, and $\ensuremath{\alpha}$-particle competition in the deexcitation of the compound system and are reproduced qualitatively by particle evaporation calculations.

The Brown-Roberts-Wells (BRW) Arc System can be compared to spatial navigation because both utilize the concept of direction to and spatial location of a point in space by referencing to a horizontal angle (azimuth) and a vertical angle (declination) relative to the horizon. The BRW system also permits the determination of the distance from a reference surface of the arc system to the point (target). The methods of determining these parameters are explained in detail with illustrations.

Percutaneous stereotactic rhizotomy (PSR) as a method of treatment of trigeminal neuralgia has gained popularity in recent years as techniques of electrode placement and lesion production have improved. However, undesirable side effects including major and minor paresthesias, trigeminal motor root weakness, diplopia, and keratitis continue to occur even in cases where the neuralgia is treated successfully. In an attempt to improve treatment further, we have developed an electrode with a flexible curved tip for PSR of the trigeminal nerve. Once the electrode and the cannula are positioned in the retrogasserian portion of the trigeminal nerve with a standardized technique, manipulation of the electrode about its 360° axis readily enables an infinite variety of position adjustments of the electrode tip. This capability enables easier and more precise electrode placement and lesion production. Undesirable lesions of the motor root may be avoided. A curved electrode has been used in 150 patients. The incidence of masseter weakness is 7.3% in this series, compared to 24% in our series of 700 patients treated with a straight electrode. The incidence of undesirable paresthesias has decreased from 27% to 10.6%. The immediate results obtained in patients with the curved electrode have improved. Excellent results (no pain, no side effects) have been achieved in 88% of patients, in contrast to 76% treated with the straight electrode. Application of stereotactic principles and the use of the curved electrode have enhanced the appeal of PSR for the treatment of trigeminal neuralgia.

The history and physical principles of radiofrequency (rf) lesion making are reviewed. The advantages of the rf lesion method are presented, with emphasis on its importance in small, critical regions such as the dorsal root entry zone (DREZ). The evolution and specifications of a satisfactory DREZ rf electrode are described. DREZ lesion sizes for this electrode at specific electrode tip temperatures were experimentally determined in animals and were used as a guide to determine acceptable clinical lesioning parameters. Emphasis is placed on lesion temperature monitoring and on the stability of electrode penetration into the spinal cord to achieve consistent and safe results.

Prominent intermediate structure correlations are suggested between /sup 12/C+/sup 12/C elastic and reaction channel excitation functions over a wide range of energies above the Coulomb barrier. The associated resonant states in /sup 24/Mg would have large partial widths to elastic, inelastic, and ..cap alpha..+/sup 20/Ne* channels.

Data have been obtained for the /sup 35/Cl + /sup 27/Al system at E/sub Cl/(lab) = 170 MeV in which the energy and mass of one particle is measured in coincidence with the energy of a second particle. These coincidence measurements indicate a two-body final state with kinetic energies corresponding to the Coulomb separation energy of the two fragments. The mass distribution of the two correlated fragments is symmetric about half the mass of the compound system. Such data is characteristic of a fission-like process. Similar fission-like cross sections are not observed in data obtained for this system at incident energies up to 145.6 MeV. The competition between particle evaporation and fission, assuming a rotating liquid drop fission barrier, has been calculated using the code ALICE. Such calculations are consistent with the present data. 4 figures.

Evaporation residues of reactions between /sup 24/ /sup 25/ /sup 26/Mg, /sup 27/Al, and /sup 28/Si as targets and 100--170-MeV /sup 35/Cl and 130 MeV /sup 32/S beams and also between /sup 28/Si and 117.5 MeV /sup 28/Si ions were measured at small forward angles by using a time-of-flight telescope. The mass distributions of the products show a complex structure, which is shown to vary smoothly with beam energy and target mass. A dominant decay mode of the compound nucleus can be assigned to each residue mass by using the shape of the angular distribution. An evaporation model calculation predicts qualitatively the main features of the mass distributions.

A unique target-centered arc system has been developed which combines the azimuth and declination angle approach concept of the standard BRW are with the anteroposterior, lateral and vertical movements of the earlier Todd-Wells Guide for maximal versatility of image-guided stereotaxy. The arc system mounts on the BRW floor stand and provides completely unobstructed approaches to the upper hemisphere, base of the skull, posterior fossa or cervical region. It is ideally adapted for implant ar-rays and laser surgery. A new transferable phantom pointer affords target confirmation using the BRW phantom base.

The /sup 12/C+ /sup 12/C elastic scattering has been measured for E/sub c.m./ = 14.6--31.3 MeV, theta/sub c.m./ = 30/sup 0/--110/sup 0/. The elastic data have been analyzed via a phase shift analysis, enabling the extraction of model independent sets of phase shift parameters. The extracted J/sup ..pi../ values for the intermediate structure resonances at E/sub c.m./ = 18.4, 19.3, and 20.3 MeV are 12/sup +/, 12/sup +/, and 12/sup +/ or 14/sup +/, respectively. The questions of ambiguities in the phase shift analysis and the comparison with J/sup ..pi../ values deduced from other experiments are discussed. Evidence is presented for the existence of gross structure resonances. The elastic scattering has also been analyzed using the sum-of-differences method to directly extract the total reaction cross section. The results of these analyses are compared to existing models of the origin of intermediate structure resonances.

Excitation functions of the reaction $^{12}\mathrm{C}(^{12}\mathrm{C}, p)^{23}\mathrm{Na}$ reveal a distinct set of resonances in the ${\frac{11}{2}}^{+}$, ${\frac{13}{2}}^{+}$, (${\frac{15}{2}}^{+}$), and (${\frac{17}{2}}^{+}$) members of the $^{23}\mathrm{Na}$ ${K}^{\ensuremath{\pi}}={\frac{3}{2}}^{+}$ ground-state band near ${E}_{x}(^{24}\mathrm{Mg})=25.2, 28.2, \mathrm{and} 33.3$ MeV. These plus earlier data suggest the possible existence of an excited collective band in $^{24}\mathrm{Mg}$ with very high deformation and large $^{12}\mathrm{C}$ + $^{12}\mathrm{C}$ width.

A detailed phase shift analysis of 12 C + 12 C elastic data from E cm = 5.5 to 33 MeV has revealed a pronounced sequence of gross structure resonances. They appear to form a rotational band from l = 0 to at least 16ħ, and are the dominant structural feature of the 12 C + 12 C reaction. The resonances are parametrized by a Breit-Wigner analysis and are simulated by shape-resonances in an optical potential with a secondary minimum at large radius. They are discussed in terms of shape-isometric doorway states in 24 Mg.

The $^{87}\mathrm{Sr}(t,p)^{89}\mathrm{Sr}$ reaction has been studied at a bombarding energy of 20 MeV. The lowest states excited are basically of single particle character and the corresponding ($t,p$) differential cross sections contain a mixture of $L$ values. A comparison of these cross sections to distorted wave (DW) calculations yields qualitative information concerning configuration mixing in these states based both on the magnitudes as well as the shapes of the angular distributions. Analysis of the data is made partly by a comparison of DW calculations to the observed $^{87}\mathrm{Sr}(t,p)$ differential cross section and partly by comparing experimental angular distributions of the $^{88}\mathrm{Sr}(t,p)^{90}\mathrm{Sr}$ reaction with those from $^{87}\mathrm{Sr}(t,p)$. The higher lying states observed in this experiment may be explained from the coupling of the $1{g}_{\frac{9}{2}}$ neutron hole to the multipole pairing phonons, represented by the low lying states of $^{90}\mathrm{Sr}$.

A stereotaxic guidance system has been used in conjunction with a conventional CT unit to biopsy 26 consecutive thoracic lesions. Accurate needle placement with a single manipulation occurred in 24 instances and two lesions required second passes. The technique provided adequate pathologic material with an acceptable complication rate. System advantages include the ability to approach lesions along oblique paths, controlled approach in difficult locations (mediastinal, peripheral, subscapular), capacity to biopsy small nonfluoroscopically visualized lesions, and increased speed over manual techniques.

A heavy-ion time-of-flight spectrometer has been brought into operation at the Brookhaven National Laboratory (BNL) MP Tandem-Van-de-Graaff facility. The start detector consists of a very thin plastic scintillation detector and the stop detector is a commercial surface-barrier detector. The design and operation of the spectrometry are discussed. An overall time resolution of ∼0.3 ns is found to be routinely attainable under realistic experimental conditions. Plans to include a magnetic quadropole lens in the flight path as well as the ultimate application of the spectrometer are discussed.

A new CT body stereotaxic system that is particularly suited to multiple placements of needles precisely in parallel is described. By scanning through a right triangle placed on the patient's skin, the stereotaxic method defines an entry point for the first needle placement. An articulating arm is then used to aim the needle at the entry point and hold the needle at the correct angle. The arm can be angled so that the complex approaches from one scan plane to another can be made to place needle arrays through inaccessible lesions, for instance, beneath the diaphragm. Animal and phantom studies have shown that placement of multiple needle arrays in parallel from CT scan data is possible.

Preliminary experience with a newly constructed angiographic localizer system for use in stereotactic neurosurgery is reported. This localizer ring, mounted on the BRW head ring, allows for the transformation of target points with known stereotactic coordinates (e.g., visible on computerized tomography scans) onto angiograms, as well as the determination of stereotactic coordinates of a set of points (e.g., arteriovenous malformations) indicated on at least two angiograms.