Introduction and Objectives: Several studies reported image quality difference according to the CBCT machines up to now.
But there has been few studies evaluating image quality of CBCT by using test phantom. The QUART DVT_AP phantom is designed to be used as a universal tool for quality assessment within the full range of Cone Beam CT (CBCT) which meets DIN 6868-161 of German standards.
The purpose of this study is to evaluate Image quality of two CBCT with varies protocols using Quart DVT_AP.
Materials and methods: Image quality of two CBCT machines(Ray Symphony(RAY
Ind., Ltd., Suwon, Korea) and Alphard 3030(Alphard Roentgen Ind., Ltd., Kyoto,
Japan)) with varies exposure modes was analyzed using Quart DVT_AP phantom.
Resolution, Homogeneity, CNR, MTF 10% & 50% values were compared using
DVTtec software.
Results and discussion: Homogeneity, CNR and MTF were differed among protocols and machines. Some of these three image quality Indices showed values around border line. Resolution of both CBCT showed little difference from manufacturer’s specifications.

Conclusions: Two CBCT machines showed acceptable image quality in most image quality indices. Image quality varied with exposure protocols and machines.
Introduction
CBCT는 몇 십 년 동안 치과영역에서 다양한 분야의 술전 진단 및 술후 평가를 위해 가장 많이
쓰이는 imaging modality가 되었다. 이러한 CBCT의 image quality assessment를 위해서 최근
CBCT 품질 평가를 위한 phantom들이 개발되었다. 또, 독일의 [DIN 6868-161]에서 CBCT에 대한 image quality assessment 규격을 제시하는 등의 여러 시도들에도 불구하고 아직 세계적으로 통
일된 image quality assessment 기준은 없는 실정이다. 현재까지 몇 개의 논문들이 여러 CBCT 기

계의 mode별 image quality를 평가하여 각 기계별로, 또 exposure mode 별로 image quality의
차이가 있음을 보고하였다. 그러나 test phantom을 사용하여 여러 기종의 image quality를 비교한
논문은 많지 않다. 따라서 우리는 CBCT image quality를 평가하는 규격 중 하나인 [DIN 6868-161]
를 따른 Quart DVT_AP phantom을 사용하여 Alphard 3030 CBCT와 Ray CBCT의 image quality를 resolution, CNR, MTF 세가지 값을 이용하여 평가해보고자 한다.
회사에서 제시하는 측정 5개 항목의 기준값 및 범주에 대한 객관적인 설명이 필요함
(INTRODUCTION 부분에)
The Nyquist frequency (NF) is defined as the norminal resolution capability of an x-ray system.
The NF is a value independent from dose intensity. It is contributing to the evaluation of the MTF.
For calculation, the reproduction of the 10mm PVC object is evaluated. The number of pixels p is determined over its full width b. The Nyquist Frequency v n of the reproduction is given by v n
= 1/2 * p/b, and the resolution of the reconstruction by v f
= b/p
The CNR is defined as ratio of contrast between PVC and PMMA and the corresponding mean image noise. It describes as to what extent a visual contrast can be discerned from the statistical background variations. For calculation, the measurement for Contrast C DVT and Image Noise N
DVT is required.
The CNR is calculated through the following formula:
CNR = C
DVT
/ N
DVT
The contrast C
DVT
is the difference between the mean of pixel values in a pixel line of PVC and the mean of pixel values in a pixel line of PMMA. The pixel lines close to the border between
PMMA and PVC are chosen for measurement from the same slice image as the Nyquist frequency.
Positioning and sizing of the ROI (Region Of Interset) is done according to the previous determination of the Nyquist ROI.
The Contrast is calculated through the following formula
C
DVT
= |P
PVC
– P
PMMA
|
Where

P
PVC
is the mean value of the pixel line in PVC,
P
PMMA
is the mean value of the pixel in PMMA
The Image Noise is defined as the geometrical mean of all standard deviations of pixel values in
PVC and PMMA(same ROI above).
The Image Noise is calculated through the following formula:
NDVT = Sqrt((S 2
PVC
+ S 2
PMMA
)/2)
Where
S
PVC
is the standard deviation of pixel values in PVC,
S
PMMA
is the standard deviation of pixel values in PMMA.
The homogeneity is defined as a relation between a measured basic contrast and a measure of background change within a homogenous slice. The homogeneity is measured in a slice image of disc2. For the measurement, 5 ROIs are automatically positioned by the QUART DVT_TEC software.
Five given ROIs are evaluated: the contrast C
DVT
of the central ROI is set into relation to the maximum deviation in mean pixel values of 4 peripheral ROIs from the pixel values of the central
ROI.
The MTF is defined as a measure of how the x-ray system reproduces details of an object to the image. To DIN 6868-161 the resolution indicators v50% and v10% are spatial frequencies transferred in the data set with 50% and 10% respectively of their maximum modulation. The MTF is measured with the test objects in disc1. The ROI is positioned over PMMA/ PVC/ Air.
The calculation of the MTF and the resolution indicators v
50%
and v
10%
are done according to DIN
6868-161. The value is given line pairs per millimetre(Lp/mm).
Materials and methods
Alphard3030(Alphard Roentgen Ind., Ltd., Kyoto, Japan)의 I 모드와 P 모드에서 각각 Figure1과
같이 Quart DVT_AP phantom의 위치와 방향을 설정하고 촬영을 시행하였다. I mode와 P mode의
촬영 조건은 표1과 같다. QUART DVT_ap is made of polymethylmethacrylate(PMMA) containing all required test objects for quality control. Figure 1 describes the component of disc1 containing the test objects and disc2 containing scatter radiation parts.( http://quart.de/en/test-

phantoms/dvt-cbct/g-quart-cbctap.html
의 Brochure QUART DVT)
All CBCT images were stored using DICOM 3.0 as a medical image file format(512 X 512 pixel) into a Window 7-based graphics workstation (Intel Core i5 3570, 4 GByte, calibrated 21.3-inch color monitor, resolution 1563 X 2048 pixel, NVIDIA Quadro 2000 graphic card) and subsequently transferred toward QUART DVT_TEC software for automatic image quality evaluation.
DISC 1 DISC 2
Figure 1
Discussion
이 5섯가지 각각에 대한 간략한 설명이 들어가야 함. 센터값이 기준값과 맞느냐, 센터를
중심으로 했을 때 모드별 변연별로 얼마나 차이가 나느냐. 아이디얼한 데이터 값이 무엇
이고 범주를 표시해야 한다. 이상값이 나왔을 경우 팬텀이 문제인지 기계가 문제인지 설
명이 필요하다. 디스커션에서 간략하게 5개 항목의 기준값이 주관적이라는 것이라는 것
을 설명해야. 왜 이 기준을 따랐냐를 설명해야, 가장 간편하고 정확하게 할 수 있는 점
이 있어서 따라갔다는 설명이 있어야 함.
5개 항목에 대해서는 표와 그림이 필요함. Mtf

그래프 등이 추가될 필요성.
이전 연구들에서 phantom 내부 위치에 따라 image quality가 달라진다는 보고들이 있었다. 하지
만 정작 phantom이 FOV의 중심에 놓이는 ideal한 상황만 가정했을 뿐, 이는 환자가 항상 FOV의
중심에 놓이지 않는 실제 임상과는 거리가 있다. 따라서 실제 임상 상황처럼 phantom이 FOV center의 주변부에 놓이는 상황에서 phantom 중심부의 image quality가 어떻게 달라지는 지 평가
하는 과정이 이전 연구들에 앞서 선행되어야 한다. 아직까지 CBCT의 image를 평가하는 규격이
통일되지 않았고, 현재 SEDENTEXCT의 guideline(Radiation protection No 172 Cone beam CT for dental and maxillofacial radiology(Evidence-based guidelines))과 독일의 [DIN 6868-161] 규격이
나와있을 뿐이다. Quart DVT_AP phantom은 이 중 DIN 규격을 따른 것으로 촬영된 phantom의
이미지를 QUART DVT_TEC software에서 반자동으로 분석함으로써 이미지 quality assessment를
편리하고 객관적으로 할 수 있다는 장점이 있다. 이 소프트웨어를 통해 얻을 수 있는 NF, CNR,
Homogeneity, MTF, Dose at Isocenter, Geometry Test 값들 중 이 연구에서는 FOV에 따라 수치를
모두 구할 수 있는 Nyquist Frequency, Contrast-to-Noise Ratio, Homogeneity, MTF 이 네 값에 대
해서만 분석하였다.
The NF is defined as the norminal resolution capability of an x-ray system. The CNR is defined as ratio of contrast between PVC and PMMA and the corresponding mean image noise. The homogeneity is defined as a relation between a measured basic contrast and a measure of background change within a homogenous slice. The MTF is defined as a measure of how the xray system reproduces details of an object to the image.
학술지 찾아볼 것.
Med. Phys. (Medical Physics) Impact factor 3.2
Phys. Med. Biol. (Physics in Medicine and Biology) Impact factor 2.922

Table 1. Alphard 3030 exposure protochols used in this study(mm)
FOV size
Voxel size
I mode
102 x 102 x 102
0.2
C mode
200 x 200 x 179
0.39