Beta Probe Research Articles

Simulation study of the effect of the geometrical parameters on the performance of a beta probe

Abstract An intraoperative probe is a small tool used to identify, locate, and dissect pathological lesions during surgery and confirm their removal. The most common type of probe is the gamma probe, which detects gamma-emitting sources. Despite the successful use of gamma probes in clinics, their application can be limited when the background radiation from healthy tissue nearby or the injection site is high. In these cases, the use of beta probes that detect beta-emitting radiotracers would be beneficial. The shorter range of beta radiation compared to gamma radiation would result in improved detection efficacy when background radiation is significant. In this simulation study, we examined how geometrical parameters may impact the performance of a beta probe. Our results showed that the source depth inside the phantom and detector size affected the performance of the beta probe. We also proposed and evaluated two designs of beta probes capable of adjusting their performance.

Radio-guided surgery with DROP-IN beta probe for 68Ga-PSMA, in high-risk prostate cancer patients eligible for robotic-assisted radical prostatectomy

Radio-guided surgery with DROP-IN beta probe for 68Ga-PSMA, in high-risk prostate cancer patients eligible for robotic-assisted radical prostatectomy

Computational evaluation of a novel beta radiation probe design using integrated circuits

Researchers at Texas A&M University (TAMU) have designed the radiation integrated circuit (RIC) for deployment as a new radiation detection system. Most integrated circuits are susceptible to radiation-induced failures, and decades of research have gone into solving this problem. Research at TAMU has led to a novel integrated circuit design that utilizes both radiation-hardened areas (RHAs) and radiation-sensitive areas (RSAs) to take advantage of these failures. The RSAs are susceptible to charged particle interactions, allowing the RIC to detect alpha and beta particles. However, beta particles are more penetrating compared to alpha particles, resulting in a lower interaction probability for beta particles incident on a bare RIC. In any material, the higher the beta energy, the deeper the beta particle can penetrate; therefore, the use of a wedge-shaped attenuator for beta particle detection not only increases interaction probability, but also provides the capability to perform maximum beta energy discrimination in the field. The objective of this research was to optimize the design of the RIC. Monte Carlo N-particle radiation transport code (MCNP) simulations assessed the beta particle detection and maximum energy discrimination performance of plate glass, borosilicate (Pyrex®) glass, acrylic (Lucite®), and natural rubber attenuators. In this proof-of-concept analysis, natural rubber was observed to be the optimal attenuating material for the beta probe with respect to maximum energy discrimination capability and weight, but all materials considered proved to be good candidates. The results of this study are promising and indicate the potential to achieve maximum beta particle energy discrimination of 50 keV using a wedged, natural rubber attenuator on the RIC.

Heavy Ion Charge Exchange Reactions as Probes for Beta–Decay

Peripheral heavy ion single and double charge reactions are described by fully quantum mechanical distorted wave methods. A special class of nuclear double charge exchange (DCE) reactions proceeding as a one-step reaction through a two-body process are shown to proceed by nuclear matrix elements of a diagrammatic structure as found also in 0ν2ß decay. These hadronic Majorana-type DCE reactions (MDCE) have to be distinguished from second order DCE reactions, given by double single charge exchange (DSCE) processes, resembling 2ν2ß decay. The theoretical concepts of MDCE are discussed. First results show that ion-ion DCE reactions are the ideal testing grounds for investigations of rare second order nuclear processes, giving insight into nuclear in-medium two-body correlation.

Design optimization and performances of an intraoperative positron imaging probe for radioguided cancer surgery

Extent and accuracy of surgical resection is a crucial step in operable tumor therapy. Emergence of promising specific tumor-seeking agents labeled with positron emitters is giving rise to a renewed interest for radioguided surgery using beta probes. Beta detection, due to the particle short range, allows a more sensitive and accurate tumor localization compared to gamma radiotracers. In that context, we are currently developing an intraoperative positron imaging probe using SiPM photosensors to perform tumor localization and post-operative control of the surgical cavity. Because compactness is a key feature when trying to detect positron emitters with high sensitivity in small surgical cavities, we chose to study the simplest detector design based on the use of a very thin organic scintillator coupled to the photosensor. Different designs of the positron imaging probe, including scintillator material and thickness, light spreading window and optical reflector, were investigated with Monte-Carlo simulations and measurements. Their impact on the probe performances were optimized in terms of positron sensitivity, gamma rays background noise contamination, spatial resolution and bias and uniformity. The ability of the probes to detect small radiolabeled tumors was also investigated by simulating different phantom uptake configurations.

Acquisition models in intraoperative positron surface imaging.

Intraoperative imaging aims at identifying residual tumor during surgery. Positron Surface Imaging (PSI) is one of the solutions to help surgeons in a better detection of resection margins of brain tumor, leading to an improved patient outcome. This system relies on a tracked freehand beta probe, using [Formula: see text]F-based radiotracer. Some acquisition models have been proposed in the literature in order to enhance image quality, but no comparative validation study has been performed for PSI. In this study, we investigated the performance of different acquisition models by considering validation criteria and normalized metrics. We proposed a reference-based validation framework to perform the comparative study between acquisition models and a basic method. We estimated the performance of several acquisition models in light of four validation criteria: efficiency, computational speed, spatial accuracy and tumor contrast. Selected acquisition models outperformed the basic method, albeit with the real-time aspect compromised. One acquisition model yielded the best performance among all according to the validation criteria: efficiency (1-Spe: 0.1, Se: 0.94), spatial accuracy (max Dice: 0.77) and tumor contrast (max T/B: 5.2). We also found out that above a minimum threshold value of the sampling rate, the reconstruction quality does not vary significantly. Our method allowed the comparison of different acquisition models and highlighted one of them according to our validation criteria. This novel approach can be extended to 3D datasets, for validation of future acquisition models dedicated to intraoperative guidance of brain surgery.

Small molecules and Alzheimer's disease: misfolding, metabolism and imaging.

Small molecule interactions with amyloid proteins have had a huge impact in Alzheimer's disease (AD), especially in three specific areas: amyloid folding, metabolism and brain imaging. Amyloid plaque amelioration or prevention have, until recently, driven drug development, and only a few drugs have been advanced for use in AD. Amyloid proteins undergo misfolding and oligomerization via intermediates, eventually forming protease resistant amyloid fibrils. These fibrils accumulate to form the hallmark amyloid plaques and tangles of AD. Amyloid binding compounds can be grouped into three categories, those that: i) prevent or reverse misfolding, ii) halt misfolding or trap intermediates, and iii) accelerate the formation of stable and inert amyloid fibrils. Such compounds include hydralazine, glycosaminoglycans, curcumin, beta sheet breakers, catecholamines, and ATP. The versatility of amyloid binding compounds suggests that the amyloid structure may serve as a scaffold for the future development of sensors to detect such compounds. Metabolic dysfunction is one of the earliest pathological features of AD. In fact, AD is often referred to as type 3 diabetes due to the presence of insulin resistance in the brain. A recent study indicates that altering metabolism improves cognitive function. While metabolic reprogramming is one therapeutic avenue for AD, it is more widely used in some cancer therapies. FDA approved drugs such as metformin, dichloroacetic acid (DCA), and methylene blue can alter metabolism. These drugs can therefore be potentially applied in alleviating metabolic dysfunction in AD. Brain imaging has made enormous strides over the past decade, offering a new window to the mind. Recently, there has been remarkable development of compounds that have the ability to image both types of pathological amyloids: tau and amyloid beta. We have focused on the low cost, simple to use, near infrared fluorescence (NIRF) imaging probes for amyloid beta (Aβ), with specific attention on recent developments to further improve contrast, specificity, and sensitivity. With advances in imaging technologies, such fluorescent imaging probes will open new diagnostic avenues.

A Method for Fabricating High Spatial Resolution Scintillator Arrays

Scintillators like thallium doped cesium iodide (CsI:Tl) can be fabricated in microcolumnar form using physical vapor deposition (PVD). The microcolumns channel the scintillation light to the photodetector which results in an improved spatial resolution. This has lead to widespread use of microcolumnar CsI:Tl in digital X-ray radiography. We present here a PVD-based method to aggregate microcolumns into structures called macrocolumns to form scintillator arrays suitable for use in nuclear imaging. In this novel approach, patterned substrates with shallow grooves 20 μm wide, 50 μm deep, with pitch ranging 100 - 500 μm were fabricated and adopted. CsI:Tl scintillator was vapor deposited onto these substrates. The optimal deposition parameters resulted in microcolumnar CsI:Tl, which displayed a macrocolumnar structure dictated by the underlying pattern of the substrate. Scanning electron micrographs (SEM) show that the microcolumns within the macrocolumns are highly oriented and perpendicular to the surface of the substrates. Energy resolution approaching that of a single crystal CsI:Tl was achieved. Since the microcolumns are densely packed with minimal gap, they behave as a macrocolumn or a single pixel. Our technique for fabricating scintillator arrays is a cost-effective alternative to mechanical pixelation of scintillators. This technique results in a high fill factor scintillation detector with minimized inter-macrocolumn gap, and high-yield detector arrays without issues related to material loss in mechanical pixelation. Coupling these structured scintillators to silicon photomultipliers (SiPMs) and applying Anger logic, we resolved scintillator pixels that were almost 1/10th the size of the SiPM macro-pixels. Combining this structured CsI:Tl scintillator with SiPMs results in a compact detector that is ideal for X-ray, gamma-ray, and charged particle detection, such as beta and gamma imaging probes and hand held cameras.

Characterization and Optimization of silicon photomultipliers for the development of intraoperative beta probes

This work reports the results of a comprehensive study aiming to characterize and optimize the performances of Silicon Photomultipliers (SiPM) as photodetectors for intraoperative beta detection of radiolabeled tumor tissues. In that purpose, we focused our measurements on the influence of temperature and operating voltage on dark noise (count rate and amplitude distribution), absolute photon detection efficiency and total gain of different SiPM devices from Hamamatsu. The impact of these parameters on the overall beta sensitivity of SiPM-based scintillation detectors was quantified as a function of the intensity of the incident light following a simple physical model that is shown to correspond well with measurements.

Performance of beta- and high-energy gamma probes for the detection of cancer tissue in experimental surgical resection beds

While high-energy gamma and beta probes have gained considerable attention due to their ability to detect cancerous lesions using (18)F-FDG in humans intraoperatively, it is unknown whether the sensitivity of such probes would allow the detection of remaining tumor tissue in the resection bed after removal of macroscopically evident disease. 9L tumors (13 primaries, 17 lymph node metastases) were generated at the upper thigh of Fisher 344 rats. After approximately 2weeks, microPET was performed to verify increased (18)F-FDG tumor uptake. Tumors were surgically exposed and probe readings of tumor and background tissues were performed in triplicate. To evaluate the ability to detect tiny tumor lesions, 12 tumor fragments (range 0.001-0.032g) were placed into the resection bed and measured to obtain a tumor-to-muscle ratio (TMR). Lesions were classified as positive if count rates were above 2.5 SD of muscle background. All tumor and muscle tissues were weighed and counted to obtain the "true" tumor-to-muscle background ratio (TMR(counter)) for reference. The presence or absence of tumor tissue was verified by histology. In the presence of background gamma radiation, the beta probe detected all tumor lesions with TMR greater than 2.5 SD of muscle background (TMR range 1.24-3.9 for all 41 lesions). Despite suitable shielding, lesion identification by the gamma probe was clearly limited by the presence of background radioactivity. As a result, only 11/13 primary tumors, 6/17 lymph nodes and 1/11 tumor fragments were identified above 2.5 SD of muscle background (TMR range 0.64-3.59 for all lesions). Under experimental conditions, the beta probe was capable to detect minute amounts of tumor tissue at the surface of resection beds. While clinical application of the current beta probe design may depend on the particular intraoperative circumstances including time requirements for surface scanning of resection beds, the data indicate clinical potential for novel designs of hand-held beta probes.

Novel handheld PET probes provide intraoperative localization of PET-avid lymph nodes

The accurate intraoperative localization of malignant nodes can pose a challenge to the surgical oncologist. Positron emission tomography (PET) scanning has significantly increased our ability to detect suspicious lesions. We investigated the ability of a novel, handheld tool to evaluate suspicious nodes intraoperatively and to correlate its findings with those seen on preoperative PET scan. Ten nude rats were inoculated with a lymphogenic mesothelioma tumor line and followed weekly with PET scan studies. When suspicious lymph nodes were found, animals were dissected and the intraoperative amount of tissue radiation was analyzed as "tumor-to-background ratio" (TBR) using the PET probes. The intraoperative probe was used to guide dissections and select high-risk nodes based on their specific radiotracer uptake. A total of 52 nodes were harvested; eight of these were suspicious on preoperative PET scan studies. Using a TBR of 2.5, the intraoperative probes were able to localize all suspicious nodes previously seen on PET scan. Both gamma (sensitivity: 100%; specificity: 86%; positive predictive value (PPV): 57%; negative predictive value (NPV): 100%) and beta (sensitivity: 88%; specificity: 91%; PPV: 64%; NPV: 98%) probes showed an excellent area under the curve (AUC) in the receiver operating characteristic analysis (ROC). Both probes had an AUC of 0.95 for localizing suspicious nodes on PET scan. Furthermore, the AUC for detecting malignancy for the gamma probe was 0.90 (95% confidence interval (CI), 0.83-0.99), and for the beta probe it was 0.97 (95% CI, 0.94-1.0), suggesting a better performance of the beta probe for detecting malignancy. This novel tool may be used synergistically with the PET scan examination to maximize intraoperative nodal selection and sampling.

小児期発症のIgA腎症におけるHLA-DQβ,TCRCβ遺伝子多型の関与

We have investigated associations between HLA-DQ beta and TCRC beta gene polymorphisms and IgA nephropathy in Japanese children. DNA from 33 cases of IgA nephropathy, 29 cases of nephrotic syndrome and 29 cases of healthy volunteers were analyzed by Southern blotting using HLA-DQ beta and TCRC beta probes. A 2 kb (Taq I) polymorphic band that hybridized to the DQ beta probe was predominant in patients of IgA nephropathy (p < 0.05) compared to the controls. The 10 kb (Bgl II) polymorphic band of TCRC beta was also predominantly present (but not significantly) in the DNA of these patients. Proteinuria in IgA nephropathy patients was found to be associated with this 10 kb TCR polymorphism. We conclude that the HLA-DQ beta and TCR genes make major contributions to the genetic pathogenesis of IgA nephropathy in Japanese children.

Development of 68Ga-labeled mannosylated human serum albumin (MSA) as a lymph node imaging agent for positron emission tomography

Although many sentinel lymph node (SLN) imaging agents labeled with (99m)Tc have been developed, no positron-emitting agent has been specifically designed for SLN imaging. Furthermore, the development of the beta probe and the requirement for better image resolution have increased the need for a positron-emitting SLN imaging agent. Here, we describe the development of a novel positron-emitting SLN imaging agent labeled with (68)Ga. A mannosylated human serum albumin (MSA) was synthesized by conjugating α-d-mannopyranosylphenyl isothiocyanate to human serum albumin in sodium carbonate buffer (pH 9.5), and then 2-(p-isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid was conjugated to synthesize NOTA-MSA. Numbers of mannose and NOTA units conjugated in NOTA-MSA were determined by matrix-assisted laser desorption ionization time-of-flight mass spectrometry. NOTA-MSA was labeled with (68)Ga at room temperature. The stability of (68)Ga-NOTA-MSA was checked in labeling medium at room temperature and in human serum at 37°C. Biodistribution in normal ICR mice was investigated after tail vein injection, and micro-positron emission tomography (PET) images were obtained after injecting (68)Ga-NOTA-MSA into a tail vein or a footpad. The numbers of conjugated α-d-mannopyranosylphenyl isothiocyanate and 2-(p-isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid units in NOTA-MSA were 10.6 and 6.6, respectively. The labeling efficiency of (68)Ga-NOTA-MSA was greater than 99% at room temperature, and its stability was greater than 99% at 4 h. Biodistribution and micro-PET studies of (68)Ga-NOTA-MSA showed high liver and spleen uptakes after intravenous injection. (68)Ga-NOTA-MSA injected into a footpad rapidly migrated to the lymph node. (68)Ga-NOTA-MSA was successfully developed as a novel SLN imaging agent for PET. NOTA-MSA is easily labeled at high efficiency, and subcutaneously administered (68)Ga-NOTA-MSA was found to migrate rapidly to the lymph node.

An Analysis of the Utility of Handheld PET Probes for the Intraoperative Localization of Malignant Tissue

IntroductionThe intraoperative localization of suspicious lesions detected by positron emission tomography (PET) scan remains a challenge. To solve this, two novel probes have been created to accurately detect the 18F-FDG radiotracer intraoperatively. MethodsNude rats were inoculated with mesothelioma. When PET scans detected 10-mm tumors, animals were dissected and the PET probes analyzed the intraoperative radiotracer uptake of these lesions as tumor to background ratio (TBR). ResultsThe 17 suspicious lesions seen on PET scan were localized intraoperatively (by their high TBR) using the PET probes and found malignant on pathology. Interestingly, smaller tumors not visualized on PET scan were detected intraoperatively by their high TBR and found malignant on pathology. Furthermore, using a TBR threshold as low as 2.0, both gamma (sensitivity, 100%; specificity, 80%; positive predictive value (PPV), 96%; and negative predictive value (NPV), 100%) and beta (sensitivity, 100%; specificity, 60%; PPV, 93%; and NPV, 100%) probes reliably detected suspicious lesions on PET scan imaging. They also showed an excellent area under the curve of 0.9 and 0.97 (95% CI of 0.81–0.99 and 0.93–1.0) for gamma and beta probes, respectively, in the receiver operating characteristic analysis for detecting malignancy. ConclusionThis novel tool could be used synergistically with a PET scan imaging to maximize tissue selection intraoperatively.

A beta-scintillator for surface measurements of radiotracer kinetics in the intact rodent cortex

β+-sensitive probes are useful tools for the measurement of radiotracer kinetics in small animals. They allow the cost-effective development of new PET tracers and offer the possibility to investigate a variety of cerebral processes. The study's main aim was the in vivo evaluation of a probe system for cerebral surface acquisitions. The detector system is a 0.2-mm thick scintillating disk of 3-mm diameter, positioned close to the cerebral surface. The study consists of 4 subparts: (1) simulation of the detection volume, (2) direct comparison with the classic intracortical beta probe regarding its capability to acquire kinetic data, (3) test of the ability to detect local tracer accumulations during infraorbital nerve (ION) electrostimulation and (4) demonstration of the feasibility to measure tracer kinetics in awake animals. Kinetic data acquired with 18F-fluorodeoxyglucose and 15O-H2O were fitted with standard compartment models. The surface probe measurements were in good agreement with those obtained using the intracortical scintillator. ION electrostimulation induced a marked increase in tracer accumulation adequately detected by the surface probe. In the head-fixed animal, a marked change in FDG kinetics was detected between the awake and anesthetized state. The novel surface probe system proved to be a valuable instrument for in vivo radiotracer studies of the cerebral cortex. Its main advantage is the absence of any tissue damage. In addition, serial acquisitions of tracer kinetics in the awake animal turned out to be feasible.

Portable PET probes are a novel tool for intraoperative localization of tumor deposits

BackgroundPositron emission tomography (PET) identifies cancer deposits by detecting sites of gamma emissions that are released from radioactively labeled molecules targeting tumor to formulate a PET image. Correlating preoperative PET scans with intraoperative findings remains a challenge. We investigated whether high-energy gamma emissions detected by a novel hand-held PET probe would detect tumors and offer a real-time method to localize tumor intraoperatively. Furthermore, we investigated the novel beta probe, which detects emissions at a shorter range than gamma emissions, making them undetectable by PET scanners, but potentially valuable for close range intraoperative detection of tumor deposits.MethodsSix-to-eight-week-old athymic mice were injected with one of four possible tumor cell lines: gastric, pancreas, squamous cell and breast cancer. After tumors reached at least 1 cm in size, they were euthanized and imaged with a micro-PET imager. Hand-held gamma and beta probes were then used in vivo and ex vivo to measure high-energy gamma and beta emissions.ResultsThe portable PET probes detected high-energy gamma and beta emissions from all tumors evaluated. These emissions were reproducible and we established that beta emissions correlate with high-energy gamma emissions and conventional PET scans. There was a strong positive correlation (R = 0.8) between gamma and beta counts. Beta emission showed a stronger correlation than gamma emission with overall tissue radioactivity.ConclusionThis study is the first to demonstrate that gamma emission detected by conventional PET imaging correlates with beta emissions. This study shows that compared to detection of gamma emissions, beta counts may offer superior real-time localization of tumor deposits. Intraoperative portable PET probe may become a useful way to exploit tumor biology and PET technology to guide real-time tissue characterization during surgery.

Expression of nicotinic acetylcholine receptors and subunit messenger RNAs in the enteric nervous system of the neonatal rat

In the enteric nervous system (ENS) excitatory nicotinic cholinergic transmission is mediated by neuronal nicotinic acetylcholine receptors (nAChR) and is critical for the regulation of gastric motility. nAChRs are ligand-gated pentameric ion channels found in the CNS and peripheral nervous system. The expression of heteromeric nAChR and receptor subunit mRNAs was investigated in the neonatal rat ENS using receptor autoradiography with the radiolabeled ligand 125I-epibatidine, and in situ hybridization with subtype specific probes for ligand binding alpha (α2, α3, α4, α5, α6) and structural beta (β2, β3, β4) subunits. The results showed strong nicotine sensitive binding of 125I-epibatidine around the stomach, and small and large intestines. The binding was partially displaced by A85380, a nicotinic ligand which differentiates between different heteromeric nAChR subtypes, suggesting a mixed receptor population. Radioactive in situ hybridization detected expression of α3, α5, α7, β2 and β4 mRNA in the myenteric plexus of the stomach, and small and large intestines. In the submucosal plexus of the small and large intestines expression of α3, α5 and β4 was found in some ganglia. There was no signal for α4, α6 and β3 in the ENS but positive hybridization signal for α2 transcripts was seen in some areas of the small intestines. However, the signal was not associated with any ganglion cells. The results confirm the presence of heteromeric nAChRs in the ENS similar to those found in the peripheral nervous system, with the majority being composed of α3(α5)β4, and a few α3β2 nAChRs. In addition, homomeric α7 nAChRs could be present.

A handy time alignment probe for timing calibration of PET scanners

Accurate time alignment of detectors in PET scanners is required for improving overall coincidence timing resolution. This is mandatory to reduce the coincidence time window of the scanner and limit as much as possible the rate of random events in images. Several techniques have been proposed so far, but most have shortcomings relating to difficult use, collection of huge amount of data or long acquisition times, not to mention transport regulation of radioactive source embedded in time alignment probes. A handy liquid scintillation beta probe was developed to overcome these problems. It consists of a PMT coupled to a small glass container that can be filled with a liquid scintillation cocktail loaded with radioactivity (such as 18F). The PMT signal is processed by an analog CFD and a digital TDC supplying an accurate timestamp on positron detection. When tested in coincidence with a fast PMT/plastic detector, a timing resolution of 1.1 ns FWHM was obtained using a standard off-the-shelf liquid cocktail having a scintillation decay time of 6.2 ns. For time alignment, coincidences are recorded between positron detected by the probe and one of the two 511 keV annihilation photons reaching detectors in the scanner. Using this simple probe, it is possible to determine the time offsets for individual LYSO and LGSO crystals in LabPET ™ scanners in about 15 min. Due to its ease of use and short acquisition time, the proposed timing calibration method was found ideal for tuning the APD bias of individual detectors to reach optimal timing resolution on every channel.

A Dual Scintillator - Dual Silicon Photodiode Detector Module for Intraoperative Gamma\\Beta Probe and Portable Anti-Compton Spectrometer

A new approach has been investigated for the miniaturization and simplification of intraoperative gamma and beta probes that have recently found application in radioguided surgery and sentinel lymph node biopsy. The probe design that is based on dual annular scintillators coupled to specially designed silicon concentric dual photodiode (CDPD). This approach allows us to avoid fiber optics coupling and PMTs. Two channels readout front-end electronics including shaper amplifier attached directly to the back of the detector module has been proposed. Two geometries of Si dual photodiodes coupled to CsI(Tl) annular scintillators with light masking between them were fabricated and investigated. CDPDs have size 10 and 6 mm as well as 6 and 3 mm outer and inner diameters respectively. The spectroscopy properties of CDPD separately and coupled to CsI(Tl) dual scintillator were investigated on I-125, Co-57 and Na-22 photon sources. Both detectors have demonstrated acceptable energy resolution (10% for 511-keV) for the proposed application with FDG isotopes. In the smaller detector the amplitude of the 511 keV photopeak from outer detector was less than in inner and is related to the light collection in the current geometry. When used in coincidence mode operation we observe a significant reduction in the measured Compton continuum level relative to the photopeak which is not significantly attenuated. The spatial resolution of detector module measured in the horizontal plane was 2-mm FWHM using a 0.5-mm collimated Tc-99m source.

Physical Performance of an Intraoperative Beta Probe Dedicated to Glioma Radioguided Surgery

The precise delineation and excision of brain tumor extent allows to improve survival outcome and quality of life of surgically treated patients. In order to refine the resection of gliomas, we are developing a novel intraoperative probe specifically dedicated to the localization of residual tumor after the bulk has been excised. The probe, built around clear and plastic scintillating fibers, was designed to detect positrons emitted from radiolabeled brain tissue in order to discriminate more specifically neoplastic from normal tissues. The probe was also built to be directly coupled to the excision tool leading to simultaneous detection and removal of tumor. We report here performances of the first radio-isotopic configuration of the intraoperative probe which consists of a detection head composed of eight detection elements held around the excision tool in a closed packed annular arrangement. This head is coupled to an optic fiber bundle that exports the scintillating light to a multi-channel photomultiplier tube. The gamma ray background generated by the annihilation of beta+ in tissues is eliminated by a real-time subtraction method. The detector exhibits a beta sensitivity of 139 cps/kBq and a gamma ray rejection efficiency of 99.5%. The ability of the probe to detect residual lesions was evaluated with a realistic brain phantom representing the surgical cavity and the boundaries of the tumor. We showed that lesions as small as 5 mm in diameter can be detected for tumor to normal tissue uptake ratios of fluorinated tracers greater than 3.5. This ratio is achieved with radiopharmaceuticals like 18F-FET or 18F-choline. These promising results suggest that the features of our system are compatible with in situ localization of residual radiolabeled tumors.