Ray Imaging Research Articles

Comparison of the imaging performances for recently developed monolithic scintillators: CRY018 and CRY019 for dual isotope gamma ray imaging applications

The growing interest for new scintillation crystals with outstanding imaging performances (i.e. resolution and efficiency) has suggested the study of recently discovered scintillators named CRY018 and CRY019. The crystals under investigation are monolithic and have shown enhanced characteristics both for gamma ray spectrometry and for Nuclear Medicine imaging applications such as the dual isotope imaging. Moreover, the non-hygroscopic nature and the absence of afterglow make these scintillators even more attractive for the potential improvement in a wide range of applications. These scintillation crystals show a high energy resolution in the energy range involved in Nuclear Medicine, allowing the discrimination between very close energy values. Moreover, in order to prove their suitability of being powerful imaging systems, the imaging performances like the position linearity and the intrinsic spatial resolution have been evaluated obtaining satisfactory results thanks to the implementation of an optimized algorithm for the images reconstruction.

Report of 14 cases of exogenous lipoid pneumonia in the elderly

Objective To investigate the clinical characteristics of exogenous lipoid and to explore the characteristics of the elderly with the disease. Methods 14 cases of elderly patients with exogenous lipoid in Beijing Hospital were analyzed. Results Among the 14 patients(7 male and 7 female), main symptoms included dyspnea(50.0%), cough(35.7%), and the common signs were crackles(28.6%)and wet rales(21.4%). For exogenous lipoid pneumonia, the most common causes of inhalation of lipoid substances included chronic constipation, nasal cavity diseases such as rhinitis(35.7%). Some of elderly dementia patients may wrong inhale lipoid substances(21.4%). X ray or CT features of exogenous lipoid showed a tumor-like mass or lesions(42.9%)and the exudative plaque(64.3%), both of which were easily misdiagnosed as tumor.All of the 14 cases(100%)were misdiagnosed as pneumonia or , and finally confirmed by pathological diagnosis.Among the 14 cases, 2 cases were diagnosed by cytopathology of bronchial alveolar lavage fluid or by transbronchial lung biopsy, 10 cases were diagnosed by invasive examination methods like lobe resection, and 2 cases were confirmed by autopsy.At present, there is still a lack of effective treatment methods for exogenous lipoid pneumonia. Conclusions Due to the basal disease(such as constipation)action, the elderly may easily have access to exogenous lipoid with atypical symptoms, might have more serious manifestations than younger adults, and may have X ray or CT imaging similar to lung cancer or pneumonia.So it is often misdiagnosed.If the patients cannot be timely diagnosed and the causes cannot be removed, it is likely to cause chronic interstitial fibrosis or death.Clinicians must increase the awareness of, and take into account the possibility of lipoid pneumonia, especially meeting the elderly patients with dry cough and dyspnea, rales or crackles and X-ray or CT tumor-like imaging as main manifestation resembling pulmonary inflammation or tumor without treatment futility after common antibiotic treatment. Key words: Lung disease, interstitial; Lipids

Coating Thickness Characterization of Composite Materials Using Terahertz Waves

Recently, terahertz ray imaging has emerged as one of the most promising new powerful nondestructive evaluation (NDE) techniques for the area applications. In this study, a new time-domain spectroscopy system was utilized for measuring the coating thickness on CFRP composite laminates. Extensive experimental measurements in reflection mode were made to map out the T-ray images. Also, the refractive index was estimated based on the electromagnetic properties. The CFRP composite laminates were observed in reflection mode and limitations will be discussed in the T-ray processing. By using these characterized material properties, the characteristics was successfully demonstrated for T-ray behavior propagating through the Shim Stock films for acquiring the refractive index. The T-ray technique has been developed for the measurement of the thickness of the Shim Stock films and the coating thickness on CFRP composites. Good results have been obtained in tests made on the thickness of the standard film samples with the coating thickness ranging from around hundreds of μm.

Hybrid Pixel-Waveform (HPWF) Enabled CdTe Detectors for Small Animal Gamma-Ray Imaging Applications.

This paper presents the design and preliminary evaluation of small-pixel CdTe gamma ray detectors equipped with a hybrid pixel-waveform (HPWF) readout system for gamma ray imaging applications with additional discussion on CZT due to its similarity. The HPWF readout system utilizes a pixelated anode readout circuitry which is designed to only provide the pixel address. This readout circuitry works in coincidence with a high-speed digitizer to sample the cathode waveform which provides the energy, timing, and depth-of-interaction (DOI) information. This work focuses on the developed and experimentally evaluated prototype HPWF-CdTe detectors with a custom CMOS pixel-ASIC to readout small anode pixels of 350 μm in size, and a discrete waveform sampling circuitry to digitize the signal waveform induced on the large cathode. The intrinsic timing, energy, and spatial resolution were experimentally evaluated in this paper in conjunction with methods for depth of interaction (DOI) partitioning of the CdTe crystal. While the experimental studies discussed in this paper are primarily for evaluating HPWF detectors for small animal PET imaging, these detectors could find their applications for ultrahigh-resolution SPECT and other imaging modalities.

Application of digital simulator in radiation field verification of intensity modulated radiation therapy

Objective To test whether the treatment volume is consistent with the target volume under digital simulator. Methods The patients were divided into head and neck, thoracic, and abdominal cancer groups, with 30 cases in each group, and the radiation fields were verified. The 0°and 90°digital reconstructed radiograph (DRR) images reconstructed by treatment planning system (TPS) was transported to digital simulator. The simulator bed was moved from reference point for positioning to isocenter point for radiotherapy. Then the 0° and 90°X ray images were collected. 2D/2D matching program was applied to accommodate the region of interest (ROI). A 10 cm×10 cm area in the radiotherapy field was set as the ROI, and the 0° and 90° DRR images matched with the corresponding X ray image automatically or manually. The bony structures of ROI in the two corresponding images were verified for consistence, and the correction error between the two images was calculated. Results The error after radiation field verification and correction error were analyzed in each group. The error was less than 3 mm on X, Y and Z axis in head and neck cancer group and less than 5 mm in thoracic and abdominal cancer group, respectively. Conclusions The digital simulator can verify the treatment volume and guarantee the accuracy during radiotherapy, which satisfy the clinical requirements. Key words: Conformal intensity modulated radiation therapy; Digital simulator; Radiation field verification; Error

Giant lobes of Centaurus A as seen in radio andγ-ray images obtained with theFermi-LAT andPlancksatellites

The γ -ray data of Fermi -LAT on the giant lobes of Centaurus A are analysed together with the high frequency radio data obtained with the Planck satellite. The large γ -ray photon statistics, accumulated during seven years of observations, and the recently updated Fermi -LAT collaboration software tools allow substantial extension of the detected γ -ray emission towards higher energy, up to 30 GeV, and lower energy, down to 60 MeV. Moreover, the new γ -ray data allow us to explore the spatial features of γ -ray emission of the lobes. For the north lobe, we confirm, with higher statistical significance, our earlier finding on the extension of γ -ray emission beyond the radio image. Moreover, the new analysis reveals significant spatial variation of γ -ray spectra from both lobes. On the other hand, the Planck observations at microwave frequencies contain important information on spectra of synchrotron emission in the cutoff region, and thus allow model-independent derivation of the strength of the magnetic field and the distribution of relativistic electrons based on the combined γ -ray and radio data. The interpretation of multiwavelength spectral energy distributions of the lobes within a pure leptonic model requires strong enhancement of the magnetic field at the edge of the south lobe. Alternatively, a more complex, leptonic-hadronic model of the γ -ray emission, postulating a non-negligible contribution of the π 0 -decay component at highest energies, can explain the γ -ray data with a rather homogeneous distribution of the magnetic field over the giant lobes.

Wrist arthroscopy assisted reduction and Herbert screw fixation for the treatment of type B distal radius fractures

To explore the clinical efficacy of internal fixation with arthroscope assistance in type B fractures of distal radius. From June 2013 to July 2015, 28 cases of type B distal radius fracture patients were enrolled into the study, including 15 males and 13 females with an average age of 45.3 years old ranging from 17 to 69 years old. These patients were treated with manipulative and poking reduction wrist arthroscopy, internal fixation with Herbert screws and repair of articular soft tissue, and the course of disease was 4 to 7 days after injury. Injured patients had the typical signs of distal radius fracture with confirming of X ray and CT imaging. Finally, no other fractures, no neurovascular injury, no other severe diseases and no surgical cortraindications were identified. According to the classification of AO/OTA, there were 8 cases of type B1, 7 cases of type B2, 13 cases of type B3. Patients were followed up for fracture healing, wrist joint function recovery, and curative effect. The 28 cases of type B distal radius fractures were followed up with an average of(12.1±1.4) months, all fractures were healed, palmer tilt angle was(15.2±3.4)°, ulnar drift angles was(20.4±6.4)°. Wrist functions were evaluated according to Cooney system and rated as excellent in 21 cases, good in 5 cases and fair in 2 cases. Intraoperative arthroscopy showed the tear of scapholunate ligaments in 3 cases, tear of in lunotriguetal ligaments in 1 case, and TFCC tear in 16 cases. Wrist arthroscopy assisted treatment of distal radius fracture type B can make the recovery of joint surface roughness to a great extent. The application of Herbert screw brings in the small trauma, and the postoperative recovery time is short, reducing the incidence of traumatic arthritis and preventing the chronic pain or inastbility of the wrist in the future.

Applying the new gamma ray imager diagnostic to measurements of runaway electron Bremsstrahlung radiation in the DIII-D Tokamak (invited).

A new gamma ray imager (GRI) is developed to probe the electron distribution function with 2D spatial resolution during runaway electron (RE) experiments at the DIII-D tokamak. The diagnostic is sensitive to 0.5-100 MeV gamma rays, allowing characterization of the RE distribution function evolution during RE growth and dissipation. The GRI consists of a lead "pinhole camera" mounted on the DIII-D midplane with 123 honeycombed tangential chords 20 cm wide that span the vessel interior. Up to 30 bismuth germanate (BGO) scintillation detectors capture RE bremsstrahlung radiation for Pulse Height Analysis (PHA) capable of discriminating up to 20 000 pulses per second. Digital signal processing routines combining shaping filters are performed during PHA to reject noise and record gamma ray energy. The GRI setup and PHA algorithms will be described and initial data from experiments will be presented. A synthetic diagnostic is developed to generate the gamma ray spectrum of a GRI channel given the plasma information and a prescribed distribution function. Magnetic reconstructions of the plasma are used to calculate the angle between every GRI sightline and orient and discriminate gamma rays emitted by a field-aligned RE distribution function.

Nanoagonist-mediated endothelial tight junction opening: A strategy for safely increasing brain drug delivery in mice

Even though opening endothelial tight junctions is an efficient way to up-regulate brain drug delivery, the extravasation of blood-borne components from the compromised tight junctions can result in adverse consequences such as edema and neuronal injuries. In this work, we developed a nanoagonist that temporarily opened tight junctions by signaling adenosine 2A receptor, a type of G protein-coupled receptor expressed on brain capillary endothelial cells. Magnetic resonance imaging demonstrated remarkable blood–brain barrier permeability enhancements and significantly increased brain uptakes of both small molecular and macromolecular paramagnetic agents after nanoagonist administration. Gamma ray imaging and transmission electron microscope observed tight junction opening followed by spontaneous recovery after nanoagonist treatment. Immunofluorescence staining showed the unspoiled basal membrane, pericytes and astrocyte endfeet that enwrapped the vascular endothelium. Importantly, edema, apoptosis and neuronal injuries observed after hypertonic agent mediated tight junction-opening were not observed after nanoagonist intervention. The uncompromised neurovascular units may prevent the leakage of blood-borne constituents into brain parenchyma and accelerate tight junction recovery. Considering blood–brain barrier impermeability is a major obstacle in the treatment of central nervous system diseases, nanoagonist-mediated tight junction opening provides a promising strategy to enhance brain drug delivery with minimized adverse effects.

Preliminary Research of CZT Based PET System Development in KAERI

Background: For positron emission tomography (PET) application, cadmium zinc telluride (CZT) has been investigated by several institutes to replace detectors from a conventional system using photomultipliers or Silicon-photomultipliers (SiPMs). The spatial and energy resolution in using CZT can be superior to current scintillator-based state-of-the-art PET detectors. CZT has been under development for several years at the Korea Atomic Energy Research Institute (KAERI) to provide a high performance gamma ray detection, which needs a single crystallinity, a good uniformity, a high stopping power, and a wide band gap. Materials and Methods: Before applying our own grown CZT detectors in the prototype PET system, we investigated preliminary research with a developed discrete type data acquisition (DAQ) system for coincident events at 128 anode pixels and two common cathodes of two CZT detectors from Redlen. Each detector has a 19.4×19.4×6 mm3 volume size with a 2.2 mm anode pixel pitch. Discrete amplifiers consist of a preamplifier with a gain of 8 mV·fC-1 and noise of 55 equivalent noise charge (ENC), a CR-RC4 shaping amplifier with a 5 μs peak time, and an analog-to-digital converter (ADC) driver. The DAQ system has 65 mega-sample per second flash ADC, a self and external trigger, and a USB 3.0 interface. Results and Discussion: Characteristics such as the current-to-voltage curve, energy resolution, and electron mobility life-time products for CZT detectors are investigated. In addition, preliminary results of gamma ray imaging using 511 keV of a 22Na gamma ray source were obtained. Conclusion: In this study, the DAQ system with a CZT radiation sensor was successfully developed and a PET image was acquired by two sets of the developed DAQ system.

SFERA: An Integrated Circuit for the Readout of X and <inline-formula> <tex-math notation="LaTeX">$\gamma $ </tex-math> </inline-formula>-Ray Detectors

In this work we present SFERA, a low-noise fully-programmable 16 channel readout ASIC designed for both X- and $\gamma $ -ray spectroscopy and imaging applications. The chip is designed to process signals coming from solid-state detectors and CMOS preamplifiers. The design has been guided by the use of Silicon Drift Detectors (SDDs) and CUBE charge sensitive amplifiers (CSAs), although we consider the ASIC sufficiently versatile to be used with other types of detectors. Five different gains are implemented, namely $2800~e^{-}$ , $4400~e^{-}$ , $10000~e^{-}$ , $14000~e^{-}$ and $20000~e^{-}$ , considering the input connected to a 25 fF feedback capacitance CMOS preamplifier. Filter peaking times ( $\mathrm {t}_{P}$ ) are also programmable among 0.5, 1, 2, 3, 4 and 6 $\mu \mathrm {s}$ . Each readout channel is the cascade of a 9th order semi-Gaussian shaping-amplifier (SA) and a peak detector (PKS), followed by a dedicated pile-up rejection (PUR) digital logic. Three data multiplexing strategies are implemented: the so-called polling X , intended for high-rate X-ray applications, the polling $\gamma $ , for scintillation light detection and the sparse , for signals derandomization. The spectroscopic characterization has shown an energy resolution of 122.1 eV FWHM on the Mn- $\mathrm {K}_{\alpha }$ line of an 55Fe X-ray source using a $10~\mathrm {mm}^{2}$ SDD cooled at −35 °C at $4~\mu \mathrm {s}$ filter peaking time. The measured resolution is 130 eV at the peaking time of 500 ns. At 1 Mcps input count rate and 500 ns peaking time, we have measured 42% of processed events at the output of the ASIC after the PUR selection. Output data can be digitized on-chip by means of an embedded 12-bit successive-approximation ADC. The effective resolution of the data converter is 10.75-bit when operated at 4.5 MS/s. The chosen technology is the AMS $0.35~\mu \mathrm {m}$ CMOS and the chip area occupancy is $5\times 5~\mathrm {mm}^{2}$ .

TU-FG-BRB-07: GPU-Based Prompt Gamma Ray Imaging From Boron Neutron Capture Therapy

Purpose: The purpose of this research is to perform the fast reconstruction of a prompt gamma ray image using a graphics processing unit (GPU) computation from boron neutron capture therapy (BNCT) simulations. Methods: To evaluate the accuracy of the reconstructed image, a phantom including four boron uptake regions (BURs) was used in the simulation. After the Monte Carlo simulation of the BNCT, the modified ordered subset expectation maximization reconstruction algorithm using the GPU computation was used to reconstruct the images with fewer projections. The computation times for image reconstruction were compared between the GPU and the central processing unit (CPU). Also, the accuracy of the reconstructed image was evaluated by a receiver operating characteristic (ROC) curve analysis. Results: The image reconstruction time using the GPU was 196 times faster than the conventional reconstruction time using the CPU. For the four BURs, the area under curve values from the ROC curve were 0.6726 (A-region), 0.6890 (B-region), 0.7384 (C-region), and 0.8009 (D-region). Conclusion: The tomographic image using the prompt gamma ray event from the BNCT simulation was acquired using the GPU computation in order to perform a fast reconstruction during treatment. The authors verified the feasibility of the prompt gamma ray reconstruction using the GPU computation for BNCT simulations.

Prompt gamma ray imaging for verification of proton boron fusion therapy: A Monte Carlo study

PurposeThe purpose of this study was to verify acquisition feasibility of a single photon emission computed tomography image using prompt gamma rays for proton boron fusion therapy (PBFT) and to confirm an enhanced therapeutic effect of PBFT by comparison with conventional proton therapy without use of boron. MethodsMonte Carlo simulation was performed to acquire reconstructed image during PBFT. We acquired percentage depth dose (PDD) of the proton beams in a water phantom, energy spectrum of the prompt gamma rays, and tomographic images, including the boron uptake region (BUR; target). The prompt gamma ray image was reconstructed using maximum likelihood expectation maximisation (MLEM) with 64 projection raw data. To verify the reconstructed image, both an image profile and contrast analysis according to the iteration number were conducted. In addition, the physical distance between two BURs in the region of interest of each BUR was measured. ResultsThe PDD of the proton beam from the water phantom including the BURs shows more efficient than that of conventional proton therapy on tumour region. A 719keV prompt gamma ray peak was clearly observed in the prompt gamma ray energy spectrum. The prompt gamma ray image was reconstructed successfully using 64 projections. Different image profiles including two BURs were acquired from the reconstructed image according to the iteration number. ConclusionWe confirmed successful acquisition of a prompt gamma ray image during PBFT. In addition, the quantitative image analysis results showed relatively good performance for further study.

An Algorithmic Approach towards Chest X-Ray Image Enhancement by Global Histogram Equalization

In medical imaging, the scope of image enhancement is highly challenging. Here digital chest x –ray image are taken in a spatial domain and enhancement of the image is done through histogram equalization method. Histogram equalization is a specific case of the more general class of histogram methods. Histogram Equalization works the best when applied to images with much higher color depth like continuos data or 16 bit gray scale images. In particular, the method can lead to better views of bone structure in X-ray images that are either over or under exposed. An algorithm is proposed to enhance the chest x-ray images using Global Histogram Equalization.

Application of Oversampling to obtain the MTF of Digital Radiology Equipment.

Within the objectives of theproject Medical Image Processing for QualityAssessment ofX Ray Imaging, the present research work is aimed at developinga phantomX ray image and itsassociated processing algorithms in order to evaluatethe image quality rendered by digital X ray equipment. These tools are used to measure various image parameters, among which spatial resolution shows afundamental property that can be characterized by the Modulation Transfer Function (MTF)of an imaging system [1]. After performing a thorough literature surveyon imaging quality control in digital X film in Argentine and international publications, it was decided to adopt for this work the Norm IEC 62220 1:2003 that recommends using an image edge as a testingmethod. In order to obtain the characterizing MTF, a protocol was designedfor unifying the conditions under which the images are acquired for later evaluation. The protocol implied acquiring a radiography image by means of a specific referential technique, i.e. referred either to voltage, current, time, distance focus plate (/film?) distance, or other referential parameter, and to interpret the image through a system of computed radiology or direct digital radiology. The contribution of the work stems from the fact that, even though the traditional way of evaluating an X film image quality has relied mostly on subjective methods, this work presents an objective evaluative toolfor the images obtained with a givenequipment, followed by a contrastive analysis with the renderings from other X filmimaging sets.Once the images were obtained, specific calculations were carried out. Though there exist some methods based on the subjective evaluation of the quality of image, this work offers an objective evaluation of the equipment under study. Finally, we present the results obtained on different equipment.

Novel methods for estimating 3D distributions of radioactive isotopes in materials

In recent years, various gamma-ray visualization techniques, or gamma cameras, have been proposed. These techniques are extremely effective for identifying “hot spots” or regions where radioactive isotopes are accumulated. Examples of such would be nuclear-disaster-affected areas such as Fukushima or the vicinity of nuclear reactors. However, the images acquired with a gamma camera do not include distance information between radioactive isotopes and the camera, and hence are “degenerated” in the direction of the isotopes. Moreover, depth information in the images is lost when the isotopes are embedded in materials, such as water, sand, and concrete. Here, we propose two methods of obtaining depth information of radioactive isotopes embedded in materials by comparing (1) their spectra and (2) images of incident gamma rays scattered by the materials and direct gamma rays. In the first method, the spectra of radioactive isotopes and the ratios of scattered to direct gamma rays are obtained. We verify experimentally that the ratio increases with increasing depth, as predicted by simulations. Although the method using energy spectra has been studied for a long time, an advantage of our method is the use of low-energy (50–150keV) photons as scattered gamma rays. In the second method, the spatial extent of images obtained for direct and scattered gamma rays is compared. By performing detailed Monte Carlo simulations using Geant4, we verify that the spatial extent of the position where gamma rays are scattered increases with increasing depth. To demonstrate this, we are developing various gamma cameras to compare low-energy (scattered) gamma-ray images with fully photo-absorbed gamma-ray images. We also demonstrate that the 3D reconstruction of isotopes/hotspots is possible with our proposed methods. These methods have potential applications in the medical fields, and in severe environments such as the nuclear-disaster-affected areas in Fukushima.

Gamma ray imager on the DIII-D tokamak

A gamma ray camera is built for the DIII-D tokamak [J. Luxon, Nucl. Fusion 42, 614 (2002)] that provides spatial localization and energy resolution of gamma flux by combining a lead pinhole camera with custom-built detectors and optimized viewing geometry. This diagnostic system is installed on the outer midplane of the tokamak such that its 123 collimated sightlines extend across the tokamak radius while also covering most of the vertical extent of the plasma volume. A set of 30 bismuth germanate detectors can be secured in any of the available sightlines, allowing for customizable coverage in experiments with runaway electrons in the energy range of 1-60 MeV. Commissioning of the gamma ray imager includes the quantification of electromagnetic noise sources in the tokamak machine hall and a measurement of the energy spectrum of background gamma radiation. First measurements of gamma rays coming from the plasma provide a suitable testbed for implementing pulse height analysis that provides the energy of detected gamma photons.

Silicon Photomultiplier-Based Multi-Channel Gamma Ray Detector Using the Dynamic Time-Over-Threshold Method

Silicon photomultipliers (SiPMs), which are a relatively new type of photon detector, have received more attention in the fields of nuclear medicine and high-energy physics because of their compactness and high gain up to 106. In this work, a SiPM-based multi-channel gamma ray detector with individual read out based on the dynamic time-over-threshold (dToT) method is implemented and demonstrated as an elemental material for large-area gamma ray imager applications. The detector consists of 64 channels of KETEK SiPM PM6660 (6 × 6 mm2 containing 10,000 micro-cells of 60 × 60 μm2) coupled to an 8 × 8 array of high-energy resolution Gd3(Al,Ga)5O12(Ce) (HR-GAGG) crystals (10 × 10 × 10 mm3) segmented by a 1 mm thick BaSO4 reflector. To produce a digital pulse containing linear energy information, the dToT-based read-out circuit consists of a CR-RC shaping amplifier (2.2 μs) and comparator with a feedback component. By modelling the pulse of the SiPM, the light output, and the CR-RC shaping amplifier, the integral-non-linearity (INL) was numerically calculated in terms of the delay time and the time constant of dynamic threshold movement. The experimental results of the averaged INL and energy resolution were 5.8±1.6% and the full-width-at-half-maximum (FWHM) of 7.4±0.9% at 662 keV, respectively. The 64-channel single-mode detector module was successfully implemented, demonstrating potential for its use as an elemental material for large-area gamma ray imaging applications.

CMOS Pixel Spectroscopic Circuits for Cd(Zn)Te Gamma Ray Imagers

A family of 2-D pixel CMOS ASICs have been developed to be used as readout electronics of gamma ray imaging instruments based on hybrid pixel sensor arrays. One element of the sensor array consists of a pixilated single crystal of CdTe or CdZnTe semiconductor bump bonded to the CMOS electronic circuit. The first member of the family can process single photon signals which deliver up to 4fCb charge, while the two other can process signals up to 36fCb. A unique readout mode and the simultaneous extraction of energy and time tagging information of the converted photons differentiate the members of this family from other existing CMOS readout circuits.

A system of gamma ray imaging devices with coded apertures

We describe a system consisting of two CdTe based gamma cameras with coded apertures and a video camera. The system is used for the localization of radioactive sources with the aid of triangulation. The methods used and the performance of the system are analyzed.