Jong Hwi Jeong

HDRK-MAN: A WHOLE BODY VOXEL MODEL BASED ON HIGH-RESOLUTION COLOR SLICE IMAGES OF A KOREAN ADULT MALE CADAVER

In a previous study, we constructed a male reference Korean phantom; HDRK-Man (High-Definition Reference Korean-Man), to represent Korean adult males for radiation protection purposes. In the present study, a female phantom; HDRK-Woman (High-Definition Reference Korean-Woman), was constructed to represent Korean adult females. High-resolution color photographic images obtained by serial sectioning of a 26 year-old Korean adult female cadaver were utilized. The body height and weight, the skeletal mass, and the dimensions of the individual organs and tissues were adjusted to the reference Korean data. The phantom was then compared with the International Commission on Radiological Protection (ICRP) female reference phantom in terms of calculated organ doses and organ-depth distributions. Additionally, the effective doses were calculated using both the HDRK-Man and HDRK-Woman phantoms, and the values were compared with those of the ICRP reference phantoms.

A polygon-surface reference Korean male phantom (PSRK-Man) and its direct implementation in Geant4 Monte Carlo simulation

Even though the hybrid phantom embodies both the anatomic reality of voxel phantoms and the deformability of stylized phantoms, it must be voxelized to be used in a Monte Carlo code for dose calculation or some imaging simulation, which incurs the inherent limitations of voxel phantoms. In the present study, a voxel phantom named VKH-Man (Visible Korean Human-Man), was converted to a polygon-surface phantom (PSRK-Man, Polygon-Surface Reference Korean-Man), which was then adjusted to the Reference Korean data. Subsequently, the PSRK-Man polygon phantom was directly, without any voxelization process, implemented in the Geant4 Monte Carlo code for dose calculations. The calculated dose values and computation time were then compared with those of HDRK-Man (High Definition Reference Korean-Man), a corresponding voxel phantom adjusted to the same Reference Korean data from the same VKH-Man voxel phantom. Our results showed that the calculated dose values of the PSRK-Man surface phantom agreed well with those of the HDRK-Man voxel phantom. The calculation speed for the PSRK-Man polygon phantom though was 70-150 times slower than that of the HDRK-Man voxel phantom; that speed, however, could be acceptable in some applications, in that direct use of the surface phantom PSRK-Man in Geant4 does not require a separate voxelization process. Computing speed can be enhanced, in future, either by optimizing the Monte Carlo transport kernel for the polygon surfaces or by using modern computing technologies such as grid computing and general-purpose computing on graphics processing units programming.

Experimental Test of Double-Layer Method for Industrial SPECT

Abstract In industrial-type single-photon-emission computed tomography (SPECT) systems, the use of relatively large detectors and collimators for effective detection of high-energy gammas significantly limits imaging performance, primarily because of insufficient measurement points. In the present study, a simple but very effective image-quality improvement method, the double-layer method, was tested. In this method, two layers of identical SPECT systems are employed in order to increase the number of measurement points and, thereby, improve the image quality. For experimentation, the two identical detector layers were arranged for 30 deg of rotation with respect to each other. The results showed that the double-layer method indeed significantly improves the image quality of the industrial SPECT system, substantially reducing errors in source size and location for both low-energy (99mTc) and high-energy (113mIn) gamma sources.

Development of new two-dosimeter algorithm for effective dose in ICRP Publication 103.

The two-dosimeter method, which employs one dosimeter on the chest and the other on the back, determines the effective dose with sufficient accuracy for complex or unknown irradiation geometries. The two-dosimeter method, with a suitable algorithm, neither significantly overestimates (in most cases) nor seriously underestimates the effective dose, not even for extreme exposure geometries. Recently, however, the definition of the effective dose itself was changed in ICRP Publication 103; that is, the organ and tissue configuration employed in calculations of effective dose, along with the related tissue weighting factors, was significantly modified. In the present study, therefore, a two-dosimeter algorithm was developed for the new ICRP 103 definition of effective dose. To that end, first, effective doses and personal dosimeter responses were calculated using the ICRP reference phantoms and the MCNPX code for many incident beam directions. Next, a systematic analysis of the calculated values was performed to determine an optimal algorithm. Finally, the developed algorithm was tested by applying it to beam irradiation geometries specifically selected as extreme exposure geometries, and the results were compared with those for the previous algorithm that had been developed for the effective dose given in ICRP Publication 60.

Feasibility study on hybrid medical imaging device based on Compton imaging and magnetic resonance imaging

In this paper, we propose a combined Compton camera/magnetic resonance imaging (MRI) scanner. For this, the table-top Compton camera currently under development in our laboratory is suitable, considering that it is not very large (i.e., a table-top size) and that it uses semiconductor detectors (for both the scatterer and absorber detectors), which in principle are not very sensitive to a magnetic field. The Compton camera takes three-dimensional images from a fixed position and, therefore, does not require a large ring-type structure, making it possible to fit it into an existing MRI system, without requiring major modifications to the system. In the present study, the potential of combining the table-top Compton camera and an MRI scanner for real simultaneous imaging was demonstrated by fusing a Compton camera image of an instance of multi-tracing, generated by using Geant4 Monte Carlo simulations, with an MR image.

Construction of a High-quality Voxel Model VKH-Man Using Serially Sectioned Images from Visible Korean Human Project in Korea

In this study, a high-quality voxel model of a Korean adult male was constructed using the Visible Korean Human (VKH) project’s serially sectioned anatomical images. The VKH images are transverse color photographs obtained from the serial sectioning of an adult Korean male cadaver (164 cm, 55 kg) at 0.2 mm intervals. A total of 28 organs and tissues were segmented with the color photographic images. The height and weight of the constructed voxel model, VKH-Man, is 164 cm and 59.6 kg, respectively. The voxel resolution of the model is 1.875 mm × 1.875 mm × 2 mm. The developed model was implemented into a Monte Carlo particle transport simulation code, MCNPX, to calculate the organ and tissue doses and, thereby, the effective doses, and the calculated values were compared with the values obtained from other computational models (KTMAN-2, VIP-Man, and ICRP-74).

Continuously Deforming 4D Voxel Phantom for Realistic Representation of Respiratory Motion in Monte Carlo Dose Calculation

We propose a new type of computational phantom, the “4D voxel phantom,” for realistic modeling of continuous respiratory motion in Monte Carlo dose calculation. In this phantom, continuous respiratory motion is realized by linear interpolation of the deformation vector fields (DVFs) between the neighboring original phases in the 4D CT data of a patient and by subsequent application of the DVFs to the phase images or to the reference image to produce multiple inter-phase images between the neighboring original phase images. A 4D voxel phantom is a combination of high-temporal-resolution voxel phantoms and on-the-fly dose registration to the reference phase image. In the course of particle transport simulation, the dose or deposited energy is directly registered to the reference phase image on-the-fly (i.e., after each event) using a DVF for dose registration. In the present study, we investigated two methods - DRP (DIR [deformable image registration] with respect to Reference Phase image) and DNP (DIR with respect to Neighboring original Phase image) - for production of multiple inter-phase images or high-temporal-resolution voxel phantoms. Utilizing these two methods, two 4D voxel phantoms each with 100 phases were produced from the original 10-phase images of the 4D CT data of a real patient in order to compare the two methods and to test the feasibility of the 4D voxel phantom methodology in general. We found that it is possible to produce a 4D voxel phantom very rapidly (i.e., <;40 min on a 4-core personal computer for a 100-phase phantom) in a fully automated process. The dose calculation results showed that the constructed 100-phase 4D voxel phantoms provide cumulative-dose distributions very similar to those of the conventional 10-phase approach for stationary proton-beam irradiation. The passing rates of the dose distributions of the 4D voxel phantoms were higher than 99.9% according to the 3% and 3 mm gamma criteria, which results validate the 4D voxel phantom methodology. The point-and dose-tracking analysis data showed that the DRP method, which uses the minimal number of DIR operations but uses inverse DVFs, provides significantly better results than those of the DNP method, which uses only DIR to generate the DVFs for inter-phase image generation and dose registration. The present study also showed that the computation time does not significantly increase when the number of phases in the 4D voxel phantom is increased for more realistic representation of continuous respiratory motion; the only significant increase is in the memory occupancy, which grows almost linearly with the number of phases.

A validation of computational phantoms from photographic images for patient-tailored whole body counting

This study attempted to validate a new method for patient-tailored efficiency calibration. Digital calibration with Monte Carlo simulations was used to substitute the lack of precision limitation due to the limited number of experimental phantoms in whole body counting calibration for internal dosimetry. The validity of this approach was examined by comparing the simulation results to the measured values from actual measurements using family BOMAB phantoms. The computational voxel phantoms were constructed by a reconstruction technique using AP and lateral photographic images of the BOMAB phantoms, instead of using the given specifications provided with BOMAB phantoms. Although discrepancies to a certain degree between the computational simulation and measured efficiencies do exist, the results support the new approach of being an alternative to family BOMAB phantoms.

Development of a Reference Korean Voxel Model by Adjusting the Size of the Organs and Tissues

The objective of this study was to adjust the height, weight, and organ and tissue sizes of a Korean voxel model in order to construct a Reference Korean voxel model. The adjustment of the height and skeletal mass was achieved by scaling the voxel dimensions. The sizes of the organs and tissues were adjusted to the Reference Korean data by adding or removing voxels on the surface. The adjusted voxel model is 171 cm in height, 68 kg in weight, which exactly matches the Reference Korean data. The size of the voxels (= voxel resolution) is 1.981 mm × 1.981 mm × 2.0854 mm. The organ and tissue masses of the adjusted model also are in a good agreement with the Reference Korean data; the differences are less than 7% for most of the organs and tissues. The unadjusted and adjusted voxel models were ported to the MCNPX Monte Carlo particle transport simulation code to calculate the equivalent doses to the organs and tissues and the effective doses. The calculated values were then compared in order to quantify the effect of the adjustment.

Stevens-Johnson syndrome developing in a girl with minimal change nephrotic syndrome on deflazacort therapy

Abstract Rationale Stevens-Johnson syndrome is a vesiculobullous disease of skin and mucosa. This generalized hypersensitivity reaction is well known to occur in association with certain drugs or viral infections. The disease is often treated with corticosteroids. However, corticosteroids induced Stevens-Johnson syndrome have been described. We present a case with nephrotic syndrome who developed cutaneous bullae and mucositis while being treated with oral deflazacort. Case report A 16-year-old girl presented with a 7-month history of recurrent generalized edema and proteinuria. She was diagnosed as minimal change nephritic syndrome. Previously she was treated with prednisolone without adverse drug reactions. 8 weeks prior to admission she developed generalized edema and was treated deflazacort 72mg daily. 1 week prior to admission she developed new eruption involving her face, trunk, and oral mucosa. Laboratory evaluation and virologic test including herpes simplex, Ebstein-Barr virus were all negative. Deflazacort was replaced by daily oral prednisolone 55mg and gradually tapered. Her skin lesion improved over 1 month period. Conclusions We present a patient with Stevens-Johnson syndrome after treatment with deflazacort. It is worth mentioning that our patient was receiving corticosteroids for minimal change nephrotic syndrome and developed the signs and symptoms of Stevens-Johnson syndrome after oral deflazacort. In our patient, deflazcort was considered as a cause because she did not take other medications.