Yeong-Cheol Heo

A Study on Effective Source-Skin Distance using Phantom in Electron Beam Therapy

In this study, for 6-20 MeV electron beam energy occurring in a linear accelerator, the authors attempted to investigate the relation between the effective source-skin distance and the relation between the radiation field and the effective source-skin distance. The equipment used included a 6-20 MeV electron beam from a linear accelerator, and the distance was measured by a ionization chamber targeting the solid phantom. The measurement method for the effective source-skin distance according to the size of the radiation field changes the source-skin distance (100, 105, 110, 115 cm) for the electron beam energy (6, 9, 12, 16, 20 MeV). The effective source-skin distance was measured using the method proposed by Faiz Khan, measuring the dose according to each radiation field (6 × 6, 10 × 10, 15 × 15, 20 × 20 ㎠) at the maximum dose depth (1.3, 2.05, 2.7, 2.45, 1.8 cm, respectively) of each energy. In addition, the effective source-skin distance when cut-out blocks (6 × 6, 10 × 10, 15 × 15 cm2) were used and the effective source-skin distance when they were not used, was measured and compared. The research results showed that the effective source-skin distance was increased according to the increase of the radiation field at the same amount of energy. In addition, the minimum distance was 60.4 cm when the 6 MeV electron beams were used with 6 × 6 cut-out blocks and the maximum distance was 87.2 cm when the 6 MeV electron beams were used with 20 × 20 cut-out blocks; thus, the largest difference between both of these was 26.8 cm. When comparing the before and after the using the 6 × 6 cut-out block, the difference between both was 8.2 cm in 6 MeV electron beam energy and was 2.1 cm in 20 MeV. Thus, the results showed that the difference was reduced according to an increase in the energy. In addition, in the comparative experiments performed by changing the size of the cut-out block at 6 MeV, the results showed that the source-skin distance was 8.2 cm when the size of the cut-out block was 6 × 6, 2.5 cm when the size of the cut-out block was 10 × 10, and 21.4 cm when the size of the cut-out block 15 × 15. In conclusion, it is recommended that the actual measurement is used for each energy and radiation field in the clinical dose measurement and for the measurement of the effective source-skin distance using cut-out blocks.

Accuracy Analysis of Magnetic Resonance Angiography and Computed Tomography Angiography Using a Flow Experimental Model

This study investigated the accuracy of magnetic resonance angiography (MRA) and computed tomography angiography (CTA) in terms of reflecting the actual vascular length. Three-dimensional time of flight (3D TOF) MRA, 3D contrast-enhanced (CE) MRA, volume-rendering after CTA and maximum intensity projection were investigated using a flow model phantom with a diameter of 2.11 mm and area of 0.26 ㎠. 1.5 and 3.0 Tesla devices were used for 3D TOF MRA and 3D CE MRA. CTA was investigated using 16 and 64 channel CT scanners, and the images were transmitted and reconstructed by volume-rendering and maximum intensity projection, followed by conduit length measurement as described above. The smallest 3D TOF MRA measure was 2.51 ± 0.12 ㎜ with a flow velocity of 40 cm/s using the 3.0 Tesla apparatus, and 2.57 ± 0.07 ㎜ with a velocity of 71.5 ㎝/s using the 1.5 Tesla apparatus; both images were magnified from the actual measurement of 2.11 ㎜. The measurement with the 16 channel CT scanner was smaller (3.83 ± 0.37 ㎜) than the reconstructed image on maximum intensity projection. The images from CTA from examination apparatus and reconstruction technique were all larger than the actual measurement.

Analysis of Images According to the Fluid Velocity in Time-of-Flight Magnetic Resonance Angiography, and Contrast Enhancement Angiography

In this study we evaluated that flow rate changes affect the (time of flight) TOF image and contrast-enhanced (CE) in a three-dimensional TOF angiography. We used a 3.0T MR System, a nonpulsatile flow rate model. Saline was used as a fluid injected at a flow rate of 11.4 cm/sec by auto injector. The fluid signal strength, phantom body signal strength and background signal strength were measured at 1, 5, 10, 15, 20 and 25-th cross-section in the experienced images and then they were used to determine signal-to-noise ratio and contrastto- noise ratio. The inlet, middle and outlet length were measured using coronal images obtained through the maximum intensity projection method. As a result, the length of inner cavity was 2.66 mm with no difference among the inlet, middle and outlet length. We also could know that the magnification rate is 49-55.6% in inlet part, 49-59% in middle part and 49-59% in outlet part, and so the image is generally larger than in the actual measurement. Signal-to-noise ratio and contrast-to-noise ratio were negatively correlated with the fluid velocity and so we could see that signal-to-noise ratio and contrast-to-noise ratio are reduced by faster fluid velocity. Signal-to-noise ratio was 42.2-52.5 in 5-25th section and contrast-to-noise ratio was from 34.0-46.1 also not different, but there was a difference in the 1st section. The smallest 3D TOF MRA measure was 2.51 ± 0.12 mm with a flow velocity of 40 cm/s. Consequently, 3D TOF MRA tests show that the faster fluid velocity decreases the signal-to-noise ratio and contrast-to-noise ratio, and basically it can be determined that 3D TOF MRA and 3D CE MRA are displayed larger than in the actual measurement.

Study of Inversion Time of Double Inversion Recovery Technique in Knee Synovial Hypertrophy: Comparison with T2-Weighted Image and PD-Weighted Image in 3.0 Tesla MR System

The purpose of this study was to aid in the diagnosis of knee synovial hypertrophy using DIR sequences without contrast agents. In the 3.0T MR system, the TI value was set to TI1/TI2 (2805/229 msec) and applied to the DIR technique. At this time, no contrast agent was used. In synovium and effusion, DIR showed higher SNR and CNR than T2WI and PDWI. In conclusion, the DIR technique using the proposed TI value is useful for the diagnosis of knee synovial hypertrophy as compared with the conventional image. In the future, this study will provide basic data in the study applying DIR technique to various diseases.

Analysis of the Brain-activation Areas During the Visual Stimulations of 2D and 3D Imagery using Functional Magnetic Resonance Imaging

The aim of this study is an functional magnetic resonance imaging (fMRI) investigation of the activity of the Brodmann brain areas during the viewing of 2D and 3D images. By using the 3.0 Tesla MRI system, an 8-channel SENSE Head Coil, and the ESys fMRI system in 5 adult males, 3D T1-weighted images were obtained from anatomic images. A gradient-EPI sequence was used for the acquisition of the brain functional images. The monitor was installed so that the images could be seen through a mirror located in the coil. The 3D appearance of the triangular, cubic, and hexagonal shapes were visually stimulated by the 2D and 3D images, and a pair of red–blue cardboard glasses was worn during the viewing of the 3D images. The display object is composed of 4 stimulus projections every 60 s and 4 resting periods of 20 s every 20 s. The acquired data were analyzed using the SPM-8 program. For the 2D imagery, the activation area of the brain is larger than that of the 3D imagery (p < .05). In the visual-cortex activation area, the number of clusters is larger for the 3D imagery (p < .05). It is expected that the basic data of this study will be used to analyze the effects of 3D-image contents on the areas of the human brain.

Study of Apparent Diffusion Coefficient Changes According to Spinal Disease in MR Diffusion-weighted Image

In this study, we compared the standardized value of each signal intensity, the apparent diffusion coefficient (ADC) that digitizes the diffusion of water molecules, and the signal to noise ratio (SNR) using b value 0 400, 1400 (s/mm²). From March 2013 to December 2013, patients with suspicion of simple compound fracture and metastatic spine cancer were included in the MR readout. We used a 1.5 Tesla Achieva MRI system and a Syn- Spine Coil. Sequence is a DWI SE-EPI sagittal (diffusion weighted imaging spin echo-echo planar imaging sagittal) image with b-factor (s/mm²) 0, 400, 1400 were used. Data analysis showed ROI (Region of Interest) in diseased area with high SI (signal intensity) in diffusion-weighted image b value 0 (s/mm²) Using the MRIcro program, each SI was calculated with images of b-value 0, 400, and 1400 (s/mm²), ADC map was obtained using Metlab Software with each image of b-value, The ADC is obtained by applying the ROI to the same position. The standardized values (SI400/SI0, SI400/SI0) of simple compression fractures were 0.47 ± 0.04 and 0.23 ± 0.03 and the standardized values (SI400/SI0, SI400/SI0) of the metastatic spine were 0.57 ± 0.07 and 0.32 ± 0.08 And the standardized values of the two diseases were statistically significant (p 0.05). In conclusion, multi - b value recognition of signal changes in diffusion - weighted imaging is very important for the diagnosis of various spinal diseases.

Dose-Decreasing Effect of the First Reversed Laser Beam Collimator for C-Arm Type Angiographic Equipment

This is a study on the dose-decreasing effect of the first reversed laser beam collimator (RLBC) for C-arm type angiographic equipment. A laser beam was located at the center of each plane at an oblique angle to the angiographic equipment detector. A field of view, which could be seen with the naked eye, was made by focusing the laser beam in the direction of the X-ray source. The height of the table was fixed at 75 cm and the iron balls were located within 2 mm of the top, bottom, left, and right edges of the output image. The time needed for location fixing, fluoroscopy, and measurement of dose area product (DAP) were compared by having 30 radiologists perform location fixing by looking at the fluoroscopic image while performing location fixing (no radiation) and while the RLBC was turned on. In the next test, the time needed for location fixing, fluoroscopy, and DAP were compared when varying the location of the iron balls from 2 to 10 mm from the edges of the output image. The results showed that the time needed for location fixing, the time needed for fluoroscopy, and DAP decreased, both in the first test and the second test. This study confirmed that the use of a RLBC for C-arm type angiographic equipment decreases both the time needed to perform the procedure and the radiation dose received. It is expected that continuous advancement of RLBC technology will contribute greatly to decreasing the dose of radiation needed and improving convenience during angiography.

Study on a method to improve T1 image contrast by the subtraction technique for 3.0 T brain examination

The purpose of this study is to describe the enhanced gray/white brain matter delineation achieved by a novel subtraction technique. We subtracted T2-weighted from T1-weighted images. The resulting images were analyzed for contrast-to-noise ratio and reader preference. Our results show superior outcomes for the subtracted images. This improvement could be used to better identify tumor enhancement or cortical dysplasia.

Effects of NEX on SNR and Artifacts in Parallel MR Images Acquired using Reference Scan

The aim of this study was to investigate effects of the number of acquisitions (NEX) on signal-to-noise (SNR) and artifacts in SENSE parallel imaging of magnetic resonance imaging (MRI). 3.0T MR System, 8 Channel sensitivity encoding (SENSE) head coils were used along with an in-vivo phantom. Reference sequence of 3D fast field echo (FFE) was consisted of NEX values of 2, 4, 6, 8, 10 and 12. The T2 turbo spin echo (TSE) sequence used for exams achieved SENSE factors of 1.2, 1.5, 1.8, 2.0, 2.2, 2.5, 2.8, 3.0, 3.2, 3.5, 3.8 and 4.0. Exams were conducted five times for each SENSE factor to measure signal intensity of the object, the posterior phase-encode direction and frequency direction. And SNR was calculated using mean values. SENSE artifacts were identified as background signal intensity in the phase-encoded direction using MRIcro. It was found that SNR increased but SENSE artifacts reduced with NEX of 4, 8 and 12 when the NEX increased in reference scan. It is therefore concluded that image quality can be improved with NEX of 4, 8 and 12 for reference scanning.