• Investigative Magnetic Resonance Imaging
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• v.18 no.2
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• pp.107-119
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• 2014

Purpose : To efficiently evaluate phased array coil performance using a software tool box with which we can make visual comparison of the sensitivity of every coil element between the real experiment and EM simulation. Materials and Methods: We have developed a $C^{{+}{+}}$- and MATLAB-based software tool called Phased Array Coil Evaluator (PACE). PACE has the following functions: Building 3D models of the coil elements, importing the FDTD simulation results, and visualizing the coil sensitivity of each coil element on the ordinary Cartesian coordinate and the relative coil position coordinate. To build a 3D model of the phased array coil, we used an electromagnetic 3D tracker in a stylus form. After making the 3D model, we imported the 3D model into the FDTD electromagnetic field simulation tool. Results: An accurate comparison between the coil sensitivity simulation and real experiment on the tool box platform has been made through fine matching of the simulation and real experiment with aids of the 3D tracker. In the simulation and experiment, we used a 36-channel helmet-style phased array coil. At the 3D MRI data acquisition using the spoiled gradient echo sequence, we used the uniform cylindrical phantom that had the same geometry as the one in the FDTD simulation. In the tool box, we can conveniently choose the coil element of interest and we can compare the coil sensitivities element-by-element of the phased array coil. Conclusion: We expect the tool box can be greatly used for developing phased array coils of new geometry or for periodic maintenance of phased array coils in a more accurate and consistent manner.

• Journal of the Korean Society of Radiology
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• v.14 no.5
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• pp.669-676
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• 2020

The purpose of this study was to analyze the changes in the values of Hounsfield Unit (HU) according to the changes in monoenergy (keV) and dilution ratio of the contrast agent, using the spectral CT. Spectral CT was used as the testing device, while 20 cc syringe phantom was used to set a total of six dilution ratios of the contrast agent: 8:2, 7:3, 6:4, 5:5, 4:6, and 3:7. Here, the non-ionic iodine solution (350 mg/ml) was used as a contrast agent. The syringe axial image was reconstructed by adjusting the obtained data on nine MonoE levels; 40 keV, 45 keV, 50 keV, 55 keV, 60 keV, 65 keV, 70 keV, 75 keV, and 80 keV. The HU values were measured at the three points of the reconstructed syringe axial image. The measurements were taken 1,620 times in total. In the analysis of the HU values according to the changes in keV and dilution ratio of the contrast agent, the highest and lowest HU values were obtained from dilution ratio 8:2 and dilution ratio 3:7, respectively, across every MonoE in the comparison of HU according to dilution ratio per MonoE (p<0.05), while the highest and lowest HU values were obtained from 40 keV and 80 keV, respectively, across all dilution ratios in the comparison of HU according to MonoE per dilution ratio (p<0.05). For the correlation per each parameter, a negative correlation of -15.014 ± 0.298 was found for HU per keV (R²=0.519) and a negative correlation of -61.372 ± 3.608 was found for HU per dilution ratio (R²=0.152) (p<0.05). To conclude, an increase in keV or dilution ratio of the contrast agent was shown to decrease the HU, and the findings in this study are anticipated to serve as the basic data in the research of HU-related parameters in Spectral CT.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.9
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• pp.117-124
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• 2015

In this paper, we introduce how to control TR, TE physical MR parameters for managing $H_1$ spin's SI(Signal Intensity) which is combined with gadolinium following administration MR agent in T1 effect for diagnostic usefulness. we used MRI phantom made with 0.5 mol Gadoteridol. This phantom was scanned by FSE sequence with different TR, TE parameters. In this study, to make T1 effect, TR was 200, 250, 300, 350, 400, 450, 500, 550, 600 msec. In addition to, TE was 6.2, 12.4, 18.6, 21.6 msec. The results were as follows ; Each RSP(Reaction Starting Point) was 100, 50, 40, 30 mmol in TE 6.2, 12.4, 18.6, 21.6 msec being irrelevant to TR. In MPSI(Max Peak Signal Intensity), 4 mmol was showed in TR 200 msec while peak signal was decreased to low concentration mol in TR 250-600 msec. In terms of RA(Reaction Area), the highest SI was TE 6.2 msec in TR 200-600msec. According to the study, we are able to recognize it is possible to control enhance rates by managing TR and TE of MR parameters; moreover, we expect that enhanced T1 image in MR clinical field can be performed in a practical way with this quantitative data.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.12
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• pp.134-141
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• 2015

The purpose on this research is quantitatively comparing and analyzing signal intensity of 1.0mol and 0.5mol contrast agent. For this study, two MR phantoms were produced. One of them is used with 1.0mol Gadobutrol. The other is used with 0.5mol Gadoteridol. These two phantoms respectively have been scanned by SE T1 sequence which is used to get a general contrast-enhanced image in 1.5T MRI and 3D FLASH sequence which is used as enhanced angio MRI. Signal intensity was measured by scanned images as per contrast agent dilution ratio. The results were as follow: RSP(Reaction Starting Point) of the two sequences(2D SE, 3D FLASH) was respectively 6.0%, 60.0% in 0.5mol contrast and 2.0%, 20.0% in 1.0mol contrast, which means in 0.5mol contrast, RSP was formed faster than the one in 1.0mol contrast. MPSI was respectively 1358.8[a.u], 1573[a.u] in 0.5mol contrast and 1374[a.u], 1642.4[a.u] in 1.0mol contrast, which means 0.5mol contrast's MPP (0.4%, 10.0%) was formed faster than 1.0mol contrast's MPP (0.16%, 1.8%). Lastly, RA as per contrast agent dilution ratio was 27.4%, 11.8% wider in 0.5mol contrast(20747.4[a.u], 23204.6[a.u]) than in 1.0mol contrast(12691.9[a.u], 20747.4[a.u]). According to the study, we are able to assure that signal reaction time of 1.0mol contrast is slower than the one of 0.5mol contrast in contrast-enhanced MRI at two different sequences(2D SE, 3D FLASH). Furthermore, owing to the fact that there are not any signal intensity differences between 1.0mol and 0.5mol contrast, it is not true that high concentration gadolinium MR contrast agent does not always mean high signal intensity in MRI.

• Journal of Radiation Protection and Research
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• v.35 no.3
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• pp.111-116
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• 2010

Ionizing radiation is most widely used for X-Ray examination among all artificial radiation exposure, it takes up the largest proportion. Even in Korea, the medical exposure by diagnostic X-Ray examination takes up 17.4% of all radiation exposure. It takes up 92% even in artificial radiation exposure. There were 111,567 cases X-Ray radiography for skull diagnosis in 2007, which is 3% annual increase since 2004. Thus, It is need to establish the diagnostic reference level and the medical facilities as a diagnostic reference level to optimize radiation protection of the patients and to reduce the doses of X-ray. In this paper, we survey patient dose on skull radiography - collected from 114 medical facilities nationwide by using human phantom and glass dosimeter. When the patient dose for the skull radiography was measured and evaluated to establish the diagnostic reference level, 2.23 mGy was established for posterior-anterior imaging and 1.87 mGy for lateral imaging was established. The posterior-anterior skull radiography entrance surface dose of 2.23 is less than the guidance level of 5 mGy from the global organizations such as World Health Organization (WHO) and International Atomic Energy Agency (IAEA), and 1.87 mGy for the lateral skull imaging is less than the guidance level of 3 mGy, which is guided by the global organizations such as World Health Organization (WHO) and International Atomic Energy Agency (IAEA).

• Progress in Medical Physics
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• v.16 no.2
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• pp.82-88
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• 2005

In this study, the physical compensator made with the high density material, Cerrobend, and the electronic compensator realized by the movement of a dynamic multileaf collimator were analyzed in order to verify the properness of a design function in the commercial RTP (radiation treatment planning) system, Eclipse. The CT images of a phantom composed of the regions of five different thickness were acquired and the proper compensator which can make homogeneous dose distribution at the reference depth was designed in the RTP. The frame for the casting of Cerrobend compensator was made with a computerized automatic styrofoam cutting device and the Millennium MLC-120 was used for the electronic compensator. All the dose values and isodose distributions were measured with a radiographic EDR2 film. The deviation of a dose distribution was $\pm0.99 cGy\;and\;\pm1.82cGy$ in each case of a Cerrobend compensator and a electronic compensator compared with a $\pm13.93 cGy$ deviation in an open beam condition. Which showed the proper function of the designed compensators in the view point of a homogeneous dose distribution. When the absolute dose value was analyzed, the Cerrobend compensator showed a $+3.83\%$ error and the electronic compensator showed a $-4.37\%$ error in comparison with a dose value which was calculated in the RTP. These errors can be admtted as an reasonable results that approve the accuracy of the compensator design in the RTP considering the error in the process of the manufacturing of the Cerrobend compensator and the limitation of a film in the absolute dosimetry.

• Progress in Medical Physics
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• v.24 no.3
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• pp.162-170
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• 2013

Dedicated single-photon emission computed tomography (SPECT) systems based on pixelated semiconductors are being developed for studying small animal models of human disease. To clarify the possibility of using a SPECT system with CdTe for a high resolution low-dose small animal imaging, we compared the quality of reconstructed images from pixelated CdTe detector to those from a small SPECT system with NaI(Tl). The CdTe detector was $44.8{\times}44.8$ mm and the pixels were $0.35{\times}0.35{\times}5$ mm. The intrinsic resolution of the detector was 0.35 mm, which is equal to the pixel size. GATE simulations were performed to assess the image quality of both SPECT systems. The spatial resolutions and sensitivities for both systems were evaluated using a 10 MBq $^{99m}Tc$ point source. The quantitative comparison with different injected dose was performed using a voxelized MOBY phantom, and the absorbed doses for each organ were evaluated. The spatial resolution of the SPECT with NaI(Tl) was about 1.54 mm FWHM, while that of the SPECT with a CdTe detector was about 1.32 mm FWHM at 30 mm. The sensitivity of NaI(Tl) based SPECT was 83 cps/MBq, while that of the CdTe detector based SPECT was 116 cps/MBq at 30 mm. The image statistics were evaluated by calculating the CNR of the image from both systems. When the injected activity for the striatum in the mouse brain was 160 Bq/voxel, the CNR of CdTe based SPECT was 2.30 while that of NaI(Tl) based SPECT was 1.85. The CNR of SPECT with CdTe was overall higher than that of the NaI(Tl) based SPECT. In addition, the absorbed dose was higher from SPECT with CdTe than those from NaI(Tl) based SPECT to acquire the same quantitative values. Our simulation results indicated that the SPECT with CdTe detector showed overall high performance compared to the SPECT with NaI(Tl). Even though the validation study is needed, the SPECT system with CdTe detector appeared to be feasible for high resolution low-dose small animal imaging.

• Investigative Magnetic Resonance Imaging
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• v.18 no.4
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• pp.303-313
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• 2014

Purpose : In-vivo conductivity reconstruction using transmit field ($B_1{^+}$) information of MRI was proposed. We assessed the accuracy of conductivity reconstruction in the presence of statistical noise in complex $B_1{^+}$ map and provided a parametric model of the conductivity-to-noise ratio value. Materials and Methods: The $B_1{^+}$ distribution was simulated for a cylindrical phantom model. By adding complex Gaussian noise to the simulated $B_1{^+}$ map, quantitative conductivity estimation error was evaluated. The quantitative evaluation process was repeated over several different parameters such as Larmor frequency, object radius and SNR of $B_1{^+}$ map. A parametric model for the conductivity-to-noise ratio was developed according to these various parameters. Results: According to the simulation results, conductivity estimation is more sensitive to statistical noise in $B_1{^+}$ phase than to noise in $B_1{^+}$ magnitude. The conductivity estimate of the object of interest does not depend on the external object surrounding it. The conductivity-to-noise ratio is proportional to the signal-to-noise ratio of the $B_1{^+}$ map, Larmor frequency, the conductivity value itself and the number of averaged pixels. To estimate accurate conductivity value of the targeted tissue, SNR of $B_1{^+}$ map and adequate filtering size have to be taken into account for conductivity reconstruction process. In addition, the simulation result was verified at 3T conventional MRI scanner. Conclusion: Through all these relationships, quantitative conductivity estimation error due to statistical noise in $B_1{^+}$ map is modeled. By using this model, further issues regarding filtering and reconstruction algorithms can be investigated for MREPT.

• Progress in Medical Physics
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• v.16 no.1
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• pp.16-23
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• 2005

The objective of this study was to construct multi-element ultrasound applicators for the treatment of gynecologic cancer with high dose rate brachytherapy. For the treatment of uterus, piezo-ceramic crystal transducer (PZT -5A) with outer diameter of 4 mm, wall thickness of 1.3 mm, and length of 24.5 mm was selected. For the treatment of cervix or vagina, it should be possible to insert the applicator into the vagina. Thus, a cylindrical PZT -8 material with outer diameter of 24.5 mm, wall thickness of 1.3 mm, and length of 15.2 mm was selected. The operating frequencies determined by vector impedance measurement were 3.2 MHz for the PZT 5A cylinder (OD=4 mm) and 1.7 MHz for the PZT -8 cylinder (OD: 24.5 mm). The ratios of generated acoustic output power to applied electric power were 33% and 61% for the tandem type crystal and the cylinder type crystal, respectively. The radiated acoustic pressure fields from both transducers were calculated using a Matlab code and measured in water using hydrophone. There was good agreement between measured and calculated acoustic pressure field distribution. For a tandem type transducer, the calculated acoustic pressure field decreased from 0.023 MPa at 10 mm to 0.010 Mpa at 30 mm, the reduction of 57%. For the cylinder type transducer which will be used for the treatment of vagina showed 78% reduction at 15 mm and 66% at 25 mm as compared to values at 5 mm from the surface. Based on the characteristics of the transducers, this study demonstrated the possibility of using the crystals as a heating source. Finally, a 3-element and 4-element prototype applicators were constructed. The 3-element applicator is 75 mm long and 4 mm thick and will be used for the treatment of uterus. The 4-element applicator is 61 mm long and 24.5 mm thick and will be used for the treatment of vagina. Using these applicators, it is possible to generate enough power to increase temperature to therapeutic level.

• Progress in Medical Physics
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• v.22 no.1
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• pp.35-41
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• 2011

For overall system test, hidden-target test have been used using film which leads to inherent analysis error. The purpose of our study is to quantify this error and to propose gel dosimeter based verification technique for 3-dimensional target point error. The phantom was made for simulation of human head and this has ability to equip 10 gel-dosimeter. $BANGkit^{TM}$ which we are able to manufacture whenever it is needed as well as to easily change the container with different shapes was used as a gel dosimeter. The 10 targets were divided into two groups based on shapes of areas with a planned 50% isodose line. All treatment and analysis was performed three times using Novalis and $BrainSCAN^{TM}$. The target point error is $0.77{\pm}0.15mm$ for 10 targets and directional target point error in each direction is $0.54{\pm}0.23mm$, $0.37{\pm}0.08mm$, $0.33{\pm}0.10mm$ in AP (anterior-posterior), LAT (lateral), and VERT (vertical) direction, respectively. The result of less than 1 mm shows that the treatment was performed through each precise step in treatment procedure. In conclusion, the 3-dimensional target point verification technique can be one of the techniques for overall system test.