A quantitative assessment of Geant4 for predicting the yield and distribution of positron-emitting fragments in ion beam therapy.

PURPOSE: To compare the accuracy with which different hadronic inelastic physics models across ten Geant4 Monte Carlo simulation toolkit versions can predict positron-emitting fragments produced along the beam path during carbon and oxygen ion therapy. Materials and Methods: Phantoms of polyethylene, gelatin or poly(methyl methacrylate) were irradiated with monoenergetic carbon and oxygen ion beams. Post-irradiation, 4D PET images were acquired and parent11C,10C and15O radionuclides contributions in each voxel were determined from the extracted time activity curves. Next, the experimental configurations were simulated in Geant4 Monte Carlo versions 10.0 to 11.1, with three different fragmentation models - binary ion cascade (BIC), quantum molecular dynamics (QMD) and the Liege intranuclear cascade (INCL++) - 30 model-version combinations. Total positron annihilation and parent isotope production yields predicted by each simulation were compared between simulations and experiments using normalised mean squared error and Pearson cross-correlation coefficient. Finally, we compared the depth of maximum positron annihilation yield and the distal point at which positron yield decreases to 50% of peak between each model and the experimental results. Results: Performance varied considerably across versions and models, with no one version/model combination providing the best prediction of all positron-emitting fragments in all evaluated target materials and irradiation conidiations. BIC in Geant4 10.2 provided the best overall agreement with experimental results in the largest number of test cases. QMD consistently provided the best estimates of both the depth of peak positron yield (10.4 and 10.6) and the distal 50%-of-peak point (10.2), while BIC also performed well and INCL generally performed the worst across most Geant4 versions. Conclusions: Best spatial prediction of annihilation yield and positron-emitting fragment production during carbon and oxygen ion therapy was found to be 10.2.p03 with BIC or QMD. These version/model combinations are recommended for future heavy ion therapy research.

Multimodal laparoscopic coincidence gamma imaging system for near-infrared fluorescence guided surgery: a preclinical study.

Purpose: Minimally invasive surgery has advantages in terms of quality of life and patient outcomes. Recently, near-infrared (NIR) fluorescence guided surgery has widely used for preclinical and clinical trials. However, NIR fluorescence has a maximum penetration capability of 10 mm. Radiographic imaging can be a solution to overcome the depth issue of NIR fluorescence. For this reason, the performance of the multimodal imaging system, which integrates annihilation gamma (511 keV) rays, NIR fluorescence, and color images, was evaluated. Approach: The multimodal imaging system consisted of a laparoscopic module, containing an internal detector for annihilation gamma events and cameras for optical imaging, and a flat module for coincidence detection with the internal detector. The acquired images were integrated by an algorithm with post image processing and registration. To evaluate the performance of the proposed multimodal imaging system, the images of a resolution target, a square bar target filled with a fluorescence dye, and a sodium-22 point source were analyzed. A preclinical test for axillary sentinel lymph node (SLN) biopsy with a rat model was conducted. Results: The spatial resolution of color images was equivalent to 4 lp/mm. The modulation transfer function of NIR fluorescence at 1 lp/mm was 0.83. The 511 keV gamma sensitivity and spatial resolution of the point source were 0.54 cps/kBq and 2.1 mm, respectively. The image of 511 keV gamma rays showed almost the same intensity regardless of the thickness of the tissue phantom. In the preclinical test, an integrated image of the SLN sample of the rat model was obtained with the proposed multimodal imaging system. Conclusions: With the proposed laparoscopic system, a merged image of the sample was obtained with the rat model. The annihilation gamma rays showed penetration capability with the tissue-mimicking phantom superior to that of NIR fluorescence.

Tracking the same fast-LGSO crystals by changing surface treatments for better coincidence timing resolution in PET.

Achieving fast coincidence timing resolution (CTR) is an important issue in clinical time-of-flight positron emission tomography (TOF-PET) to improve the reconstructed image quality. One of the major factors affecting the CTR is the crystal surface treatment, which is often parameterized as surface roughness. However, previous studies on the crystal surface treatment optimization had two limitations of crystal-by-crystal variation and worse CTR over 200 ps. Here, we report the effects of the crystal surface treatment on the performance of a 20 mm long fast-LGSO crystal based TOF detector by tracking the same crystals in the sub-180 ps CTR regime. The light collection efficiency (LCE), energy resolution (ER) and CTR of the TOF detector were evaluated with six different crystal surface treatments of chemically polished (C.P), C.P half side roughened (1/2S) treatment, and then the C.P one side roughened (1S) treatment, mechanically polished (M.P) treatment, M.P 1/2S treatment, and M.P 1S treatment. The four lateral surfaces of each crystal were wrapped by using enhanced specular reflector film while the top surface was covered by using Teflon tape. The bottom surface of the crystal was optically coupled to a silicon photomultiplier. The timing and energy signals were extracted by using a custom-made high-frequency readout circuit, and then digitized by using a waveform digitizer. All the experimental conditions were same except the crystal surface treatment. Among the six different crystal surface treatments, the M.P 1S would be the optimal crystal surface treatment which balanced enhancements in the CTR (165 ± 3 ps) and ER (10.5 ± 0.5%). Unlike the M.P 1S, the C.P 1S did not enhance the CTR and ER. Hence, the C.P without roughening would be the second-best optimal crystal surface treatment which balanced the CTR (169 ± 3 ps) and ER (10.5 ± 0.5%).

Submillimeter-Resolution PET for High-Sensitivity Mouse Brain Imaging.

PET is a powerful molecular imaging technique that can provide functional information on living objects. However, the spatial resolution of PET imaging has been limited to around 1 mm, which makes it difficult to visualize mouse brain function in detail. Here, we report an ultrahigh-resolution small-animal PET scanner we developed that can provide a resolution approaching 0.6 mm to visualize mouse brain function with unprecedented detail. Methods: The ultrahigh-resolution small-animal PET scanner has an inner diameter of 52.5 mm and axial coverage of 51.5 mm. The scanner consists of 4 rings, each of which has 16 depth-of-interaction detectors. Each depth-of-interaction detector consists of a 3-layer staggered lutetium yttrium orthosilicate crystal array with a pitch of 1 mm and a 4 × 4 silicon photomultiplier array. The physical performance was evaluated in accordance with the National Electrical Manufacturers Association NU4 protocol. Spatial resolution was evaluated with phantoms of various resolutions. In vivo glucose metabolism imaging of the mouse brain was performed. Results: Peak absolute sensitivity was 2.84% with an energy window of 400-600 keV. The 0.55-mm rod structure of a resolution phantom was resolved using an iterative algorithm. In vivo mouse brain imaging with 18F-FDG clearly identified the cortex, thalamus, and hypothalamus, which were barely distinguishable in a commercial preclinical PET scanner that we used for comparison. Conclusion: The ultrahigh-resolution small-animal PET scanner is a promising molecular imaging tool for neuroscience research using rodent models.

The OpenGATE ecosystem for Monte Carlo simulation in medical physics.

This paper reviews the ecosystem of GATE, an open-source Monte Carlo toolkit for medical physics. Based on the shoulders of Geant4, the principal modules (geometry, physics, scorers) are described with brief descriptions of some key concepts (Volume, Actors, Digitizer). The main source code repositories are detailed together with the automated compilation and tests processes (Continuous Integration). We then described how the OpenGATE collaboration managed the collaborative development of about one hundred developers during almost 20 years. The impact of GATE on medical physics and cancer research is then summarized, and examples of a few key applications are given. Finally, future development perspectives are indicated.

Feasibility of triple gamma ray imaging of10C for range verification in ion therapy.

Objective.In carbon ion therapy, the visualization of the range of incident particles in a patient body is important for treatment verification. In-beam positron emission tomography (PET) imaging is one of the methods to verify the treatment in ion therapy due to the high quality of PET images. We have shown the feasibility of in-beam PET imaging of radioactive15O and11C ion beams for range verification using our OpenPET system. Recently, we developed a whole gamma imager (WGI) that can simultaneously work as PET, single gamma ray and triple gamma ray imaging. The WGI has high potential to detect the location of10C, which emits positrons with a simultaneous gamma ray of 718 keV, within the patient's body during ion therapy.Approach.In this work, we focus on investigating the performance of WGI for10C imaging and its feasibility for range verification in carbon ion therapy. First, the performance of the WGI was studied to image a10C point source using the Geant4 toolkit. Then, the feasibility of WGI was investigated for an irradiated polymethyl methacrylate (PMMA) phantom with a10C ion beam at the carbon therapy facility of the Heavy Ion Medical Accelerator in Chiba.Main results.The average spatial resolution and sensitivity for the simulated10C point source at the centre of the field of view were 5.5 mm FWHM and 0.010%, respectively. The depth dose of the10C ion beam was measured, and the triple gamma image of10C nuclides for an irradiated PMMA phantom was obtained by applying a simple back projection to the detected triple gammas.Significance.The shift between Bragg peak position and position of the peak of the triple gamma image in an irradiated PMMA phantom was 2.8 ± 0.8 mm, which demonstrates the capability of triple gamma imaging using WGI for range verification of10C ion beams.

Optimization of GFAG crystal surface treatment for SiPM based TOF PET detector.

Coincidence timing resolution (CTR) is an important parameter in clinical positron emission tomography (PET) scanners to increase the signal-to-noise ratio of PET images by using time-of-flight (TOF) information. Lutetium (Lu) based scintillators are often used for TOF-PET systems. However, the self-radiation of Lu-based scintillators may influence the image quality for ultra-low activity PET imaging. Recently, a gadolinium fine aluminum gallate (Ce:GFAG) scintillation crystal that features a fast decay time (∼55 ns) and no self-radiation was developed. The present study aimed at optimizing the GFAG crystal surface treatment to enhance both CTR and energy resolution (ER). The TOF-PET detector consisted of a GFAG crystal (3.0 × 3.0 × 20 mm3) and a SiPM with an effective area of 3.0 × 3.0 mm2. The timing and energy signals were extracted using a high-frequency SiPM readout circuit and then were digitized using a CAMAC DAQ system. The CTR and ER were evaluated with nine different crystal surface treatments such as partial saw-cut and chemical polishing and the 1-side saw-cut was the best choice among the treatments. The respective CTR and ER of 202 ± 2 ps and 9.5 ± 0.1% were obtained with the 1-side saw-cut; the other 5-side mechanically polished GFAG crystals had respective values which were 18 ps (9.0%) and 1.3% better than those of the all-side mechanically polished GFAG crystal. The chemically polished GFAG crystals also offered enhanced CTR and ER of about 17 ps (8.2%) and 2.1%, respectively, over the mechanically polished GFAG crystals.

Initial results of a mouse brain PET insert with a staggered 3-layer DOI detector.

Objective.Small animal positron emission tomography (PET) requires a submillimeter resolution for better quantification of radiopharmaceuticals. On the other hand, depth-of-interaction (DOI) information is essential to preserve the spatial resolution while maintaining the sensitivity. Recently, we developed a staggered 3-layer DOI detector with 1 mm crystal pitch and 15 mm total crystal thickness, but we did not demonstrate the imaging performance of the DOI detector with full ring geometry. In this study we present initial imaging results obtained for a mouse brain PET prototype developed with the staggered 3-layer DOI detector.Approach.The prototype had 53 mm inner diameter and 11 mm axial field-of-view. The PET scanner consisted of 16 DOI detectors each of which had a staggered 3-layer LYSO crystal array (4/4/7 mm) coupled to a 4 × 4 silicon photomultiplier array. The physical performance was evaluated in terms of the NEMA NU 4 2008 protocol.Main Results.The measured spatial resolutions at the center and 15 mm radial offset were 0.67 mm and 1.56 mm for filtered-back-projection, respectively. The peak absolute sensitivity of 0.74% was obtained with an energy window of 400-600 keV. The resolution phantom imaging results show the clear identification of a submillimetric rod pattern with the ordered-subset expectation maximization algorithm. The inter-crystal scatter rejection using a narrow energy window could enhance the resolvability of a 0.75 mm rod significantly.Significance.In an animal imaging experiment, the detailed mouse brain structures such as cortex and thalamus were clearly identified with high contrast. In conclusion, we successfully developed the mouse brain PET insert prototype with a staggered 3-layer DOI detector.

Performance evaluation of a staggered three-layer DOI PET detector using a 1 mm LYSO pitch with PETsys TOFPET2 ASIC: comparison of HAMAMATSU and KETEK SiPMs.

In this study, we propose a staggered three-layer depth-of-interaction (DOI) detector with a 1 mm crystal pitch and 19.8 mm total crystal thickness for a high-resolution and high-sensitivity small animal in-beam PET scanner. A three-layered stacked LYSO scintillation array (0.9 × 0.9 × 6.6 mm3crystals, 23 × 22 mm2surface area) read out by a SiPM array (8 × 8 channels, 3 × 3 mm2active area/channel and 50µm microcell size) with data acquisition, signal processing and digitization performed using the PETsys Electronics Evaluations kit (based on the TOFPET v2c ASIC) builds a DOI LYSO detector block. The performance of the DOI detector was evaluated in terms of crystal resolvability, energy resolution, and coincidence resolving time (CRT). A comparative performance evaluation of the staggered three-layer LYSO block was conducted with two different SiPM arrays from KETEK and HAMAMATSU. 100% (KETEK) and 99.8% (HAMAMATSU) of the crystals were identified, by using a flood irradiation the front- and back-side. The average energy resolutions for the 1st, 2nd, and 3rd layers were 16.5 (±2.3)%, 20.9(±4.0)%, and 32.7 (±21.0)% (KETEK) and 19.3 (±3.5)%, 21.2 (±4.1)%, and 26.6 (±10.3)% (HAMAMATSU) for the used SiPM arrays. The measured CRTs (FWHM) for the 1st, 2nd, and 3rd layers were 532 (±111) ps, 463 (±108) ps, and 447 (±111) ps (KETEK) and 402 (±46) ps, 392 (±54) ps, and 408 (±196) ps (HAMAMATSU). In conclusion, the performance of the staggered three-layer DOI detector with 1 mm LYSO pitch and 19.8 mm total crystal thickness was fully characterized. The feasibility of a highly performing readout of a high resolution DOI PET detector via SiPM arrays from KETEK and HAMAMATSU employing the PETsys TOFPET v2c ASIC could be demonstrated.

A staggered 3-layer DOI PET detector using BaSO4reflector for enhanced crystal identification and inter-crystal scattering event discrimination capability.

The spatial resolution of small animal positron emission tomography (PET) scanners can be improved by the use of crystals with fine pitch and rejection of inter-crystal scattering (ICS) events, which leads to a better quantification of radiopharmaceuticals. On the other hand, depth-of-interaction (DOI) information is essential to preserve the spatial resolution at the PET field-of-view (FOV) periphery while keeping the sensitivity. In this study we proposed a novel staggered 3-layer DOI detector using BaSO4reflector material for an enhanced crystal identification performance as well as ICS event rejection capability over those of ESR reflector based DOI detectors. The proposed staggered 3-layer DOI detector had 3-layer staggered LYSO crystal arrays (crystal pitch = 1 mm), an acrylic light guide, and a 4 × 4 SiPM array. The 16 SiPM anode signals were read out by using a resistive network to encode the crystal position and energy information while the timing signal was extracted from the common cathode. The crystal map quality was substantially enhanced by using the BaSO4reflector material as compared to that of the ESR reflector due to the low optical crosstalk between the LYSO crystals. The ICS events can be rejected with BaSO4by using simple pulse height discrimination thanks to the light collection efficiency difference that depends on the crystal layers. As a result, the total number of events was decreased around 26% with BaSO4as compared to that of ESR. The overall energy resolution and coincidence timing resolution with BaSO4were 19.7 ± 5.6% and 591 ± 160 ps, respectively which were significantly worse than 10.9 ± 2.2% and 308 ± 23 ps values of ESR because of the relatively low light collection efficiency with BaSO4(1057 ± 308 ADC) compared to that of ESR (1808 ± 118 ADC). In conclusion, we found the proposed staggered 3-layer DOI detector using the BaSO4reflector material with ICS event rejection capability can be a cost-effective solution for realizing high resolution and highly sensitive small animal PET scanners while minimizing the complexity of the SiPM readout circuit.

SiPM-based gamma detector with a central GRIN lens for a visible/NIRF/gamma multi-modal laparoscope.

Intraoperative imaging has been studied using conventional devices such as near infrared (NIR) optical probes and gamma probes. However, these devices have limited depth penetration and spatial resolution. In a previous study, we realized a multi-modal endoscopic system. However, charge-coupled device (CCD)-based gamma imaging required long acquisition times and lacked gamma energy information. A silicon photomultiplier (SiPM)-based gamma detector is implemented in a multi-modal laparoscope herein. A gradient index (GRIN) lens and CCD are used to transfer and readout visible and NIR photons. The feasibility of in-vivo sentinel lymph node (SLN) mapping was successfully performed with the proposed system.

Design consideration of compact cardiac TOF-PET systems: a simulation study.

Myocardial perfusion imaging (MPI) with PET plays a vital role in the management of coronary artery disease. High sensitivity systems can contribute to maximizing the potential value of PET MPI; therefore, we have proposed two novel detector arrangements, an elliptical geometry and a D-shape geometry, that are more sensitive and more compact than a conventional large-bore cylindrical geometry. Here we investigate two items: the benefits of the proposed geometries for cardiac imaging; and the effects of scatter components on cardiac PET image quality. Using the Geant4 toolkit, we modeled four time-of-flight (TOF) PET systems: an 80 cm diameter cylinder, a 40 cm diameter cylinder, a compact ellipse, and a compact D-shape. Spatial resolution and sensitivity were measured using point sources. Noise equivalent count rate and image quality were examined using an anthropomorphic digital chest phantom. The proposed geometries showed higher sensitivity and better count rate characteristics with a fewer number of detectors than the conventional large-bore cylindrical geometry. In addition, we found that the increased intensity of the scatter components was a big factor affecting the contrast in defect regions for such a compact geometry. It is important to address the issue of the increased intensity of the scatter components to develop a high-performance compact cardiac TOF PET system.

Energy spread estimation of radioactive oxygen ion beams using optical imaging.

Radioactive ion (RI) beams combined with in-beam positron emission tomography enable accuratein situbeam range verification in heavy ion therapy. However, the energy spread of the radioactive beams generated as secondary beams is wider than that of conventional stable heavy ion beams which causes Bragg peak region and distal falloff region broadening. Therefore, the energy spread of the RI beams should be measured carefully for their quality control. Here, we proposed an optical imaging technique for the energy spread estimation of radioactive oxygen ion beams. A polymethyl methacrylate phantom (10.0 × 10.0 × 9.9 cm3) was irradiated with an15O beam (mean energy = 247.7 MeV u-1, standard deviation = 6.8 MeV u-1) in the Heavy Ion Medical Accelerator in Chiba. Three different momentum acceptances of 1%, 2% and 4% were used to get energy spreads of 1.9 MeV u-1, 3.4 MeV u-1and 5.5 MeV u-1, respectively. The in-beam luminescence light and offline beam Cerenkov light images were acquired with an optical system consisting of a lens and a cooled charge-coupled device camera. To estimate the energy spread of the15O ion beams, we proposed three optical parameters: (1) distal-50% falloff length of the prompt luminescence signals; (2) full-width at half maximum of the Cerenkov light signals in the beam direction; and (3) positional difference between the peaks of the Cerenkov light and the luminescence signals. These parameters estimated the energy spread with the respective mean squared errors of 2.52 × 10-3MeV u-1, 5.91 × 10-3MeV u-1, and 0.182 MeV u-1. The distal-50% falloff length of the luminescence signals provided the lowest mean squared error among the optical parameters. From the findings, we concluded optical imaging using luminescence and Cerenkov light signals offers an accurate energy spread estimation of15O ion beams. In the future, the proposed optical parameters will be used for energy spread estimation of other RI beams as well as stable ion beams.

Influence of momentum acceptance on range monitoring of 11C and 15O ion beams using in-beam PET.

In heavy-ion therapy, the stopping position of primary ions in tumours needs to be monitored for effective treatment and to prevent overdose exposure to normal tissues. Positron-emitting ion beams, such as 11C and 15O, have been suggested for range verification in heavy-ion therapy using in-beam positron emission tomography (PET) imaging, which offers the capability of visualizing the ion stopping position with a high signal-to-noise ratio. We have previously demonstrated the feasibility of in-beam PET imaging for the range verification of 11C and 15O ion beams and observed a slight shift between the beam stopping position and the dose peak position in simulations, depending on the initial beam energy spread. In this study, we focused on the experimental confirmation of the shift between the Bragg peak position and the position of the maximum detected positron-emitting fragments via a PET system for positron-emitting ion beams of 11C (210 MeV u-1) and 15O (312 MeV u-1) with momentum acceptances of 5% and 0.5%. For this purpose, we measured the depth doses and performed in-beam PET imaging using a polymethyl methacrylate (PMMA) phantom for both beams with different momentum acceptances. The shifts between the Bragg peak position and the PET peak position in an irradiated PMMA phantom for the 15O ion beams were 1.8 mm and 0.3 mm for momentum acceptances of 5% and 0.5%, respectively. The shifts between the positions of two peaks for the 11C ion beam were 2.1 mm and 0.1 mm for momentum acceptances of 5% and 0.5%, respectively. We observed larger shifts between the Bragg peak and the PET peak positions for a momentum acceptance of 5% for both beams, which is consistent with the simulation results reported in our previous study. The biological doses were also estimated from the calculated relative biological effectiveness (RBE) values using a modified microdosimetric kinetic model (mMKM) and Monte Carlo simulation. Beams with a momentum acceptance of 5% should be used with caution for therapeutic applications to avoid extra dose to normal tissues beyond the tumour when the dose distal fall-off is located beyond the treatment volume.

Crystal surface and reflector optimization for the SiPM-based dual-ended readout TOF-DOI PET detector.

Silicon photomultipliers (SiPMs) are now widely used for positron emission tomography (PET) applications because of their high gain and low noise characteristics. The PET image quality has been improved with the advancement of time-of-flight (TOF) and depth-of-interaction (DOI) measurement techniques. For brain-dedicated PET systems, both TOF and DOI information are beneficial for enhancing the reconstructed PET image quality. In a previous study, we proposed SiPM-based dual-ended readout PET detectors that used a mean time method to achieve coincidence timing resolution (CTR) of 349 ps and DOI resolution of 2.9 mm. However, the coincidence timing resolution (CTR) was worse than 300 ps since the crystal surface and the reflector type were not optimized. This study aimed at investigating the optimal crystal surface treatment and the reflector material to achieve a sub-200 ps CTR and sub-3 mm DOI resolution with a dual-ended readout PET detector using an LYSO crystal (2.9 × 2.9 × 20 mm3). The scintillation light inside the LYSO crystal was read out by two SiPMs using the dual-ended readout method. The CTR and DOI resolution were measured with two different crystal surfaces (polished and saw-cut) and three different reflector material scenarios of ESR without grease (i.e., air coupling), ESR with optical grease and Teflon. We digitized the timing and energy signals by using a V775N TDC module (35 ps bit-1) and V965 QDC module, respectively. The combination of the saw-cut LYSO crystal and the ESR with air coupling resulted in the best CTR (188 ± 32 ps) and DOI resolution (2.9 ± 0.2 mm) with the dual-ended readout configuration. We concluded the dual-ended readout method in combination with the saw-cut crystal and the ESR reflector with air coupling can provide a sub-200 ps CTR and sub-3.0 mm DOI resolution simultaneously.

Optical imaging for the characterization of radioactive carbon and oxygen ion beams.

Heavy ion therapy is a promising cancer therapy technique due to the sharper Bragg peak and smaller lateral scattering characteristics of heavy ion beams as compared to a proton therapy. Recently, the potential for radioactive ion beam therapy has been investigated in combination with the OpenPET system to improve the accuracy of in vivo beam range verification. However, the characteristics of the radioactive ion beams have not been investigated thoroughly. Optical imaging has been proposed as a novel high-resolution beam range estimation method for heavy ion beams. In this study, high-resolution luminescence imaging and Cerenkov light imaging were performed for the range estimation of radioactive ion beams such as 11C and 15O in the Heavy Ion Medical Accelerator in Chiba (HIMAC) secondary beam line. A polymethyl methacrylate (PMMA) phantom (10.0 × 10.0 × 9.9 cm3) was irradiated by 11C and 15O ion beams. In order to obtain the in-beam luminescence and off-line beam Cerenkov light images, an optical system was used that consisted of a lens and a cooled CCD camera. The Bragg peaks and stopping positions of the 11C and 15O ion beams could be visualized by using the luminescence and Cerenkov light imaging, respectively. The Bragg peaks showed a good correlation with the peak of the luminescence profile with a positional discrepancy of 1 mm and 0.4 mm for the 11C and 15O ion beams, respectively. In conclusion, optical imaging using luminescence and Cerenkov light could be used for the precise range estimation of radioactive ion beams.

Proof-of-concept of a multimodal laparoscope for simultaneous NIR/gamma/visible imaging using wavelength division multiplexing.

An optical/nuclear hybrid surgical technique using ICG-99mTc-nanocolloid can improve lesion detectability by detecting both fluorescence and gamma signals. However, a hybrid multimodal laparoscope that can obtain both NIR and gamma images is not available yet. In this work, we present a proof-of-concept study of a prototype multimodal laparoscope that can provide simultaneous NIR/gamma/visible imaging using wavelength division multiplexing. The performances of optical and gamma imaging were evaluated using a USAF 1951 negative resolution target and 99mTc-filled tumor-like sources, respectively. Simultaneous NIR/gamma/visible images of two Eppendorf tubes containing a mixture of 99mTc-ICG are presented.

Lens implementation on the GATE Monte Carlo toolkit for optical imaging simulation.

Optical imaging techniques are widely used for in vivo preclinical studies, and it is well known that the Geant4 Application for Emission Tomography (GATE) can be employed for the Monte Carlo (MC) modeling of light transport inside heterogeneous tissues. However, the GATE MC toolkit is limited in that it does not yet include optical lens implementation, even though this is required for a more realistic optical imaging simulation. We describe our implementation of a biconvex lens into the GATE MC toolkit to improve both the sensitivity and spatial resolution for optical imaging simulation. The lens implemented into the GATE was validated against the ZEMAX optical simulation using an US air force 1951 resolution target. The ray diagrams and the charge-coupled device images of the GATE optical simulation agreed with the ZEMAX optical simulation results. In conclusion, the use of a lens on the GATE optical simulation could improve the image quality of bioluminescence and fluorescence significantly as compared with pinhole optics.

A feasibility study of an integrated NIR/gamma/visible imaging system for endoscopic sentinel lymph node mapping.

PURPOSE: The aim of this study is to integrate NIR, gamma, and visible imaging tools into a single endoscopic system to overcome the limitation of NIR using gamma imaging and to demonstrate the feasibility of endoscopic NIR/gamma/visible fusion imaging for sentinel lymph node (SLN) mapping with a small animal. METHODS: The endoscopic NIR/gamma/visible imaging system consists of a tungsten pinhole collimator, a plastic focusing lens, a BGO crystal (11 × 11 × 2 mm3 ), a fiber-optic taper (front = 11 × 11 mm2 , end = 4 × 4 mm2 ), a 122-cm long endoscopic fiber bundle, an NIR emission filter, a relay lens, and a CCD camera. A custom-made Derenzo-like phantom filled with a mixture of 99m Tc and indocyanine green (ICG) was used to assess the spatial resolution of the NIR and gamma images. The ICG fluorophore was excited using a light-emitting diode (LED) with an excitation filter (723-758 nm), and the emitted fluorescence photons were detected with an emission filter (780-820 nm) for a duration of 100 ms. Subsequently, the 99m Tc distribution in the phantom was imaged for 3 min. The feasibility of in vivo SLN mapping with a mouse was investigated by injecting a mixture of 99m Tc-antimony sulfur colloid (12 MBq) and ICG (0.1 mL) into the right paw of the mouse (C57/B6) subcutaneously. After one hour, NIR, gamma, and visible images were acquired sequentially. Subsequently, the dissected SLN was imaged in the same way as the in vivo SLN mapping. RESULTS: The NIR, gamma, and visible images of the Derenzo-like phantom can be obtained with the proposed endoscopic imaging system. The NIR/gamma/visible fusion image of the SLN showed a good correlation among the NIR, gamma, and visible images both for the in vivo and ex vivo imaging. CONCLUSION: We demonstrated the feasibility of the integrated NIR/gamma/visible imaging system using a single endoscopic fiber bundle. In future, we plan to investigate miniaturization of the endoscope head and simultaneous NIR/gamma/visible imaging with dichroic mirrors and three CCD cameras.