International Journal of Innovative Research in Advanced Engineering (IJIRAE) ISSN:

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1 COMPARISON OF RADIATION DOSE AND IMAGE QUALITY BETWEEN THE SINGLE DETECTOR CT AND MULTI DETECTOR CT ON HEAD EXAMINATION: STUDY PHANTOM Samburi Master of Physics, University of Diponegoro, Indonesia Agency of Testing For Health Facilities (BPFK Jakarta), Ministry Of Health, Indonesia Wahyu Setia Budi Department of Physics, Faculty of Science and Mathematics, University Diponegoro, Indonesia Eko Hidayanto Department of Physics, Faculty of Science and Mathematics, University Diponegoro, Indonesia Manuscript History Number: IJIRAE/RS/Vol.04/Issue04/APAE10105 Received: 19, March 2017 Final Correction: 30, May 2017 Final Accepted: 15, August 2017 Published: August 2017 Citation: Samburi; Wahyu, S. B. & Hidayanto, E. (2017), 'Comparison of Radiation Dose and Image Quality Between the Single Detector CT and Multi Detector CT on Head Examination: Study Phantom, in IJIRAE Journal. Editor: Dr.A.Arul L.S, Chief Editor, IJIRAE, AM Publications, India Copyright: 2017 This is an open access article distributed under the terms of the Creative Commons Attribution License, Which Permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Abstract Research has been done by comparing radiation dose profile and image quality to single detector CT (SDCT) and multi detector CT (MDCT). The method of measuring dose accuracy and linearity of the output dose is done by placing a dose pencil on the iso center position in the middle of the gantry. The scanning parameters use axial mode with the acquisition factor of 120 kv, mas, 1 sec rotation time and 5-10 mm slice thickness. Head Phantom CTDI diameter of 16 cm is used for CT dose index (CTDI) measurement. These measurements use a routine head examination protocol provided by CT Scan. Evaluation of image quality using fantom Gammex ACR 464. The resulting data is normalized to obtain constant image noise between SDCT and MDCT. SDCT resulted in a linearity coefficient of radiation dose output ranging from to higher than MDCT ranging from to The accuracy of DOSIS radiation at 120 kv / 100 mas from SDCT is 23.3 mgy and 31.2 mgy whereas MDCT ranges from mgy. The standard deviation of radiation dose distribution pattern with CTDI head phantom ranged from 1.7 to 5.8. While the results of image quality measurement, linearity response to 5 standard materials indicate that they are within the range of HU reference values. Evaluation of homogeneity of CT number accuracy, uniformity of noise and uniformity of CT,center and CT,edge respectively are in the range -7 and + 7 HU, 0,258 and 1,123 HU and 0,93-3,85 HU. Contrast to Noise Ratio (CNR) measurements range from In addition, the results of spatial resolution measurements range from 6-7 lp / cm. From the overall evaluation shows, that MDCT has a better score than a SDCT. However, when compared with standard reference values, a single CT detector can be retained as an imaging modality to support the patient's diagnostic process. Keywords SDCT, MDCT, Linearitas Dosis, CTDI, Kualitas Citra. IJIRAE , All Rights Reserved Page -46

2 I. INTRODUCTION Total use of CT scans in Indonesia continues to experience a significant increase from year to year. From about 7300-an X-ray machine data are registered in the Nuclear Energy Regulatory Agency (BAPETEN) in 2015, about 5-6% of that amount is the modality of CT Scan with various brands and types. From these data the amount of approximately 10% is a machine with a single detector CT (single slice CT Scan), which is still used in the examination of patients. While the rest are multi-slice CT with a variation of the dual slice to slice 128 that began circulating. Slowly and surely conventional CT displaced population and is replaced with the latest generation in line with technological developments. One problem that still complained of by the physicists is that the use of CT contributing to provide 35-45% of the dose of radiation of all existing diagnostic radiology modalities [1]. Results of research on comparative dose on conventional CT and spiral air by Bouzarjomehri F., et al, 2006, indicating the patient's radiation dose using conventional CT examination is higher than spiral CT [2]. The amount of radiation dose in CT scan parameters determined by parameters such as tube voltage (kv), tube current production - timer (mas), slice thickness (mm), rotation time and pitch. The relationship between the dose of radiation to the current production of tube-timer linear. The higher mas then the higher the output radiation from CT scans. MDCT development to further enhance the ability of CT to improve image quality and reduce radiation dose. [3]. Among the use of CT scans, CT examination was the dominant case in every hospital / clinic. More than 50% CT scan is a head examination [Lisa W]. The study of image quality and dose eyepiece using a head examination protocol with helical and sequential modes was performed by Abdeen et al (2010). The results showed that the relative helix mode resulted in smaller doses than sequential, while the image quality was relatively similar [Abdeen]. Another study in 2013, comparing different CT Scan engines to recognize some types of CT that have the lowest dose of radiation and diagnostic image quality adequate for diagnostic purposes. The study used human observers to evaluate image quality and record radiation doses from selected hospitals [Haytham Ahmad]. In line with Haytham (2013) research, we conducted the same research using a set of measuring instruments, fantom CTDI head and fantom image quality. The goal is to compare the radiation dose and image quality between a single CT detector and a multi-detector to obtain valid data about the advantages and disadvantages of both. II. METHODS A. SURVEY STUDY AND INSTRUMENTATION During the period of March 2016 s.d March 2017, we conducted a research survey of 6 CT Scans consisting of 2 types of CT single detectors and 4 Multi Slices of four different hospital radiology facilities. The six CT Scan aircraft are shown in table 1 below. Table I - Characteristics of CT model Scan survey research. Scanner Type Manufactur Model Slice Class Production A HITACHI PRATICO B TOSHIBA CXXG-010A C PHILIPS MX 4000 DUAL D TOSHIBA AQUILION E HITACHI ROBUSTA F PHILIPS MX-16 SLICE The equipment used for this study consisted of a fantom image quality accreditation, Gammex ACR 464, RTI type piranha 657 and a fantom dose CT head index (figure.1). Figure 1. The equipment used in research IJIRAE , All Rights Reserved Page -47

3 B. MEASUREMENT PARAMETER. Linearity dose calculated with linearity coefficient (CL), aims to determine the consistency of performance response of certain significant components of the x-ray plane when given different inputs. The linearity coefficient is formulated as [7]: CTDI describe the sum of all contributions dose along a line parallel to the axis of rotation of the scanner (ie the z- axis) is formulated as[8]: D (z) is the value of the dose at a given location along the z axis, N is the number of images and T is the nominal slice thickness. While the present CTDI 100 dose accumulation of multiple scans in the middle of 100 mm along the detector and does not calculate the accumulated dose of scan length exceeding 100 mm [8]. The relationship between CTDI 100 with CTDI w formulated as : CTDI 100,p showed the average doses edge and CTDI 100, c is the result of the measurement at the center. CTDI 100 relationship with CTDI V: the quantity p is called the pitch factor and is defined as the ratio of the total width of the beam (N.T) divided by increments of movement of the patient table per rotation of the tube [8]. In CT Scan some determinants of image quality characteristics are CT Number accuracy, homogeneity and contrast image resolution. According to the reference of the imagery imagery used, for CT number accuracy evaluation, CT HU reference values for polyethylene (- 95 HU), equivalent water material (0 HU), acrylic (+120 HU) and air (-1000 HU) [ACR CT ]. (Figure 2). Figure 2: CT number linearity response image. To evaluate the homogeneity of the image, the acceptance criteria mean CT number difference between the center and the edge is less than 5 HU fourth edge position. Value CT number in the middle between -7 and +7 HU HU HU selected with ± 5 [9]. IJIRAE , All Rights Reserved Page -48

4 Figure 3: Image homogeneity of CT HU. To quantify low contrast resolution is to calculate the value of contrast-to-noise ratio (CNR) is formulated with Figure 4: Low Contrast Image Resolution A Rod Where is the ROI on nodule diameter of 50 cm, and Rod B is the ROI on the left of Rod A. SD is the standard deviation value of Rod B. criterion noise level contrast ratio allowable absolute value of contrast noise ratio in adult abdominal examination protocol and adult head 1.0. Figure 5: High Contrast Image Resolusi. To assess the spatial resolution of the CT image of the scan, window width and window level (contrast and brightness) is set at 100 WW and 1100 WL. Be visually seen eight bar pattern composed resolution 4, 5, 6, 7, 8, 9, 10 and 12 lp / cm, each measuring 15 mm x 15 mm square. The acceptance criteria for the spatial resolution is a scanner capable of detecting a minimum of 6 lp / cm. IJIRAE , All Rights Reserved Page -49

5 C. Measurement Technique. Multimeter x-ray RTI piranha type 657 and pencil dose detector used for measurement accuracy and linearity of the output radiation and a phantom head CT dose index of 16 cm diameter is used for the measurement of CTDI head. For measurement of dose linearity and accuracy, the position detector is placed on the holder in the free state in the air on a gantry isocenter. First do a scan of the entire detector to obtain a projection image detector positions. Furthermore, the scanning fixed by setting 8-10 mm thick slices of the image against a predetermined area of the detector. Used tube voltage of 120 kv was fixed for the fourth variation CT with tube current of 25 ma to 300 ma. Measurements are converted to dose per rotation and CTDI in air. All measurements are normalized to 100 mas CTDIair and performed with axial mode. From this measurement process resulting output value of radiation dose at 120 kv per 100 mas and the coefficient of linearity of the output radiation. For the measurement of CT dose index used multimeter x-ray detector and a pencil and CTDI phantom head. Parameter measurements refer to the user guide of the manufacturer or using measurement information from the monitor console by using the mode of examination of the head. Measurements performed 5 times from middle position, top, right, bottom and left. The measurement results in the form of exposure dose (CTDI) is converted into a number of CT dose descriptors. Phantom image quality accreditation, Gammex ACR 464, used for evaluation of image quality assessment. Parameters assessed restricted to the measurement results CT number, low contrast resolution, homogeneity and high contrast spatial resolution. III. RESULTS AND DISCUSSION A. The output accuracy and linearity of the output radiation Point dose measurements at the free in air position detector are expressed in dosage form in units of mgy / 100mAs and linearity coefficient of radiation output. The used tube voltage is 120 kv. The measurement results are shown by Table 2. The measurement data shows that the average of the dosage in the air varies greatly, whereas for the linearity coefficient dose in air type A and type B which is the representation of CT single detector is between 0,017-0,0085 and type C, D, E and F are repren- sations of CT Multi Slices ranging from to However, the overall linearity coefficient scanner value is still below the threshold (CL Threshold 0.1). Scanner Type Table II. LINEARITY DOSE MEASUREMENT DETECTOR WITH FLOATING IN THE AIR. Tube Voltage (kv) acquisition parameter Range of Tube Current (ma) Rotation Time (sec) Slice Thicknes (mm) Average (mgy/100mas) Coeffisien of Linearity A , ,77 0,085 B , ,60 0,017 C ,0 5 11,17 0,024 D , ,57 0,018 E , ,82 0,055 F ,0 5 13,31 0,007 B. CTDI and dose distribution pattern. Measurements of CT dose index (CTDI) with the head diameter of fantom are shown in table 3 and histogram 6. The radiation dose pattern of CT Scan at 5 detector positions is shown in 6-histogram. The magnitude of the dose is influenced by various acquisition parameters, such as tube voltage (kv), tube current (ma), rotation time (sec), pitch, slice thickness and collimation options with reference to manufacturer-specified acquisition parameters, each shown on the monitor Console except for single-slice CT scanners. In general, the multi-slice CT plane on the console has provided an estimate of the main CTDI values for CTDI vol and DLP descriptors. This value is at least the physicist's reference to the radiation dose received by the patient. IJIRAE , All Rights Reserved Page -50

6 Table III CTDI DISTRIBUTION PATTERNS IN 5 POSITION DETECTORS IN MEASURING HEAD WITH FANTOM CTDI. Scanner Type The results of measurements dose (mgy) Center Top edge Right edge Bottom edge Left edge Standard Deviation A 29,94 34,16 31,81 23,43 28,85 4,61 B 44,70 49,34 45,85 41,92 43,93 3,07 C 33,12 30,37 34,39 31,35 28,93 1,79 D 25,07 39,2 34,03 32,3 36,26 5,84 E 25,92 27,49 24,64 23,59 24,87 1,68 F 40,29 40,56 40,10 35,86 38,23 2,24 Figure 1. Graph CTDI distribution pattern of four types of scanners at the 5 position of the detector with CTDI phantom head. C. Comparison of linearity response accuracy The measurement data of the CT number of the six scanners is shown in table 4, the slope curve is shown in table 5. The value of CT number is obtained from the measurement of the region of interest (ROI) to five standard materials that have certain CT HU reference value (table 4). The electron density of the five reference materials is shown in Table 4. Table IV - MEASUREMENT OF THE VALUE OF CT HU 4 TYPE SCANNER FOR RESPONSE ASSESSMENT LINEARITY. Material Electron Measured Value (CT HU) HU Density A B C D E F Reference Polyethelene 4-94, ,57-94,34-98,8-96,54-95 Bone , ,1 958, ,1 967, Air , ,96-971,26-990,2-976, Acrylic , ,96 120,17 120,1 119, Water ,26 0-2,69 1,26 2,5-0,46 0 Tabel V - LINEAR REGRESSION OF CT-HU MEASUREMENT RESULTS Tipe Scanner Nilai CT-HU Scanner Regresi Linear Polyethelene Bone Air Acrylic Water (R) A -94,34 958,53-971,26 120,17 1,26 0,996 B -98,19 962,12-996,09 122,23 2,77 0,997 C -93,57 818,1-1009,96 127,96-2,69 0,999 D -94,34 958,53-971,26 120,17 1,26 0,996 E -98,8 1110,1-990,2 120,1 2,5 0,991 F -96,54 967,16-976,75 119,59-0,46 0,996 IJIRAE , All Rights Reserved Page -51

7 Phantom scanning uses axial mode or sequential routine head examination, with a 120 kv, mas acquisition factor and 5-10 cm thick wedges. The CT-HU values generated by each scanner were compared with the reference HU and the linear regression value (R) was calculated. Limit of linearity response tolerance is expressed with value R 0,99. D. Comparison of Homogeneity CT-HU. The comparison of the images homogeneity is shown in Table 6. The data were extracted from a scan of the fantom that has a homogeneous material equivalent to water. The value of CT number is obtained from the measurement of the region of interest (ROI) on the five position of the scanned image. Phantom scanning also uses axial mode or sequential routine head checking, with a 120 kv, mas acquisition factor and 5-10 cm thick wedges. To draw closer to the same measurement parameters all scanners of homogeneity measurements were converted to acquisition parameters of 120 kv, 300 mas and 8 mm thickness of the slice. The results of the evaluation of the measurements of CT summation are shown in Table 5. From the table, it can be concluded that the CT scores of the four types of scanners are included in the range (- 7 HU and + 7 HU). Similarly, for the uniformity parameters of noise and maximum deviation of CT HU centers and edges entered in the acceptance criteria of the test (-5 CT HU and +5 CT HU). Scanner Type A B C D E F Table VI- ACCURACY AND UNIFORMITY CT NUMBER OF WATER EQUIVALENT MATERIAL. Parameter ROI Potition (CT HU) Top Edge Right Edge Left Edge Bottom Edge Center Mean ROI 0,46 0,78-0,10 0,25-0,15 Noise 3,63 3,23 3,34 3,61 3,20 Deviation Mean ROI 0,46 0,78 0,10 0,25 Noise converted 0,45 0,76-0,10 0,24 Mean ROI 3,26 3,82 3,28 2,92 3,61 Noise 4,08 4,02 3,95 3,95 4,02 Deviation Mean ROI 3,26 3,82 3,28 2,92 Noise converted 3,16 3,70 3,18 2,83 Mean ROI -0,49-4,12-4,29-2,65-4,14 Noise 3,70 3,27 3,07 3,07 3,13 Deviation Mean ROI 0,49 4,12 4,29 2,65 Noise converted -0,45-3,80-3,96-2,44 Mean ROI -0,27-1,70-1,64-1,34-1,57 Noise 5,44 3,68 3,78 3,76 3,50 Deviation Mean ROI 0,27 1,70 1,64 1,34 Noise converted -0,26-1,65-1,59-1,30 Mean ROI 1,60 2,50 2,30 1,60 2,20 Noise 3,55 2,79 2,91 2,81 2,83 Deviation Mean ROI 1,60 2,50 2,30 1,60 Noise converted 1,55 2,42 2,23 1,55 Mean ROI -3,40-3,20-2,90-2,70-3,00 Noise 2,90 2,60 2,40 2,40 2,30 Deviation Mean ROI 3,40 3,20 2,90 2,70 Noise converted -3,04-2,86-2,59-2,41 Table VII- EVALUATION OF MEASUREMENT ACCURACY CT NUMBER OF MATERIAL AND WATER EQUIVALENT NUMBER UNIFORMITY CT. Parameter Evaluation Measured Values A B C D E F Acceptance Criteria Accuracy of CT Number (water) 0,76-4,29 0,45-1,65 2,42 3,04-7 s.d +7 Noise Uniformity 0,85 0,35 3,50 1,38 0,87 0,63-5 s.d +5 Maximum Deviation (CT HU center CT HU edge) 0,78 3,28 4,29 1,70 2,50 3,40-5 s.d +5 IJIRAE , All Rights Reserved Page -52

8 E. Comparison of Low Contrast Resolution The contrast resolution can be defined as the ability of a CT-scanner to distinguish relatively large objects that differ only slightly in the density of the background. To avoid subjectivity in the assessment of low-contrast images, the quantity of contrast to noise ratio (CNR) is used. The CNR value limit for adult head examination is 1.0. The result of measurement CNR value is shown in table 8. From the table it can be concluded all scanners meet the acceptance criteria. Table VIII - CONTRAST TO NOISE RATIO VALUE. Scanner System ROI Target background ROI background noise CNR measured A 93,5 87,4 3,7 1,7 B 93,5 87,2 4,1 1,5 C 96,4 88,7 3,7 2,1 D 85,6 78,6 3,7 1,9 E 86,3 82,5 3,7 1,0 F 93,1 86,9 3,1 2,0 Acceptance Criteria 1,0 F. Comparison of Hight Contrast Resolution In this test verified the ability of scanners to detect small lesions that have very different attenuation values than the surrounding tissue. This characterizes the ability of the imaging system to distinguish between two very small objects in adjacent positions. Spatial resolution measurements are performed with objects that have high contrast from a uniform background. The criteria for acceptance of high-contrast spatial resolution of CT Scan according to AAPM with the image imagery of Gammex 464 ACR is 6 lp / cm. From the results of the test table 9, it can be concluded that all CT scans meet the acceptance of the same or above the acceptability limit. Table VIII - MEASUREMENT OF SPATIAL RESOLUTION Acquisition factors Scanner Type Spatial Resolution (lp/cm) kv mas slice A B C D ,5 5 7 E ,5 6 F Acceptance Criteria 6 lp/cm Scanner Type Spatial Resolution (lp/cm) Acceptance Criteria CT Scan A 6 CT Scan B 7 CT Scan C 6 6 (lp /cm) CT Scan D 6 IV. CONCLUSIONS The result of comparison of radiation dose and image quality of the six CT types shows that all CT Scan performance is in accordance with standard criteria. Quantitatively there is no significant difference between SDCT and MDCT. A number of other variables that affect the reliability level of CT Scanner is maintenance program, production year, frequency of use and brand of tool manufacturer. If performance grading of all six CT Scan types is seen, it is relatively superior in terms of radiation dose and image quality compared to SDCT. However, if SDCT is compared to the threshold value of passing the test of internationally accepted standards, SDCT can still be maintained as imaging modalities to support the patient's diagnostic process. In the measurement of radiation doses at 120 kvp / 100mAs, 2 types of SDCT scanners had mgy and mgy, 2 MDCT scanners scored mgy and mgy and the other two MDCT types were mgy and 13, 31 mgy. IJIRAE , All Rights Reserved Page -53

9 The CT Scan test method from BAPETEN provides dose guidance at 120 kvp / 100mAs ranging from mgy [7]. The dose range is intended to ensure adequate quality in obtaining diagnostic image quality. If you look at the measurement results, MDCT with 120 kv / 100mAs resulting in dose below that range with adequate image quality, it is necessary to propose amendment of the guidelines. The linearity coefficient of this measurement ranges from , below the guideline level threshold (CL 0.1). The standard deviation of the radiation radiation pattern at 5 detector positions shows varying values. To some extent, the higher standard deviation of the radiation distribution pattern will have an impact on the homogeneity of the image. In the image quality measurement shows all types of CT Scan meet the acceptance criteria test. The linearity response ratio shows the slope curve (R) of all CT scans at the threshold ( 0.99). Evaluation of measurement accuracy of CT number, noise uniformity and maximum deviation between edge and center HU CT is in tolerance range (± 5 HU). Low-contrast resolution is shown in CNR quantification. CNR measurement results are in the acceptance range ( 1.0). Similarly, the results of high contrast resolution measurements of all CT scans are within tolerable limits (6 lp / cm) REFERENCES 1. H. Imhof, et al., 2002, Spiral CT and radiation dose, European Journal of Radiology 47 (2003) 29_/ F.Bouzarjomehri1, et. al., 2006, Conventional and spiral CT dose indices in Yazd general hospitals, Iran, Iran. J. Radiat. Res., 2006; 3 (4): 3. S.T. Schindera, et. al, 2012 : Effect of automatic tube voltage selection on image quality and radiation dose in abdominal CT angiography of various body sizes: A phantom study, Clinical Radiology xxx (2013) e79ee Lisa Williams et al, 2005, Computed tomography of the head: An experimental study to investigate the effectiveness of lead shielding during three scanning protocols, The College of Radiographers, doi: /j.radi Abdeen et.al, 2010, Comparison of image quality and lens dose in helical and sequentially acquired head CT, Clinical Radiology 65 (2010) 868e873N. 6. Haytham Ahmad AL Ewaidat, Studies of CT Dose and Image Quality Using Clinical and Phantom Images, A thesis presented to Charles Sturt University in fulfillment of the requirements for the degree of Doctor of Philosophy, Metode Uji Pesawat Sinar-X CT Scan, KU/PD/DKKN/07, BAPETEN, AAPM REPORT No. 96, The Measurement, Reporting, and Management of Radiation Dose in CT Report of AAPM Task Group 23: CT Dosimetry Diagnostic Imaging Council CT Committee, American College of Radiology CT Accreditation Program Testing Instructions - Revised, January 6, Robert L. Dixon & John Boone, 2010 The CTDI Paradigm: A Practical Explanation for Medical Physicists, American College of Radiology Bushberg JT, Siebert JA, Leidholdt EM, et al: The Essential Physics of Medical Imaging. Baltimore, Lippincott Williams & Wilkins, Huda, W., Ogden, K., & Khorasani, M. (2008). Effect of dose metrics and radiation risk models when optimizing CT x-ray tube voltage. Physics in Medicine and Biology, 53, ImPACT. (2002). Eight and Sixteen Slice CT Scanner Comparison Report (Vol. 7). 14. ImPACT. (2003). Single Slice CT Scanner Comparison Report (Vol. 8). European Commission s Study Group. (1998). 15. ImPACT. (2005). Sixteen slice CT scanner comparison report (Vol. 12). 16. Jaengsri Nuttawan, 2004, CT Protocol, Radiology Departement Of Takshin Hospital, Bangkok Neseth R., 2000, Procedurs and Documentation for CT and MRI, CIC Edizioni Internazionali. 17. Johns H.E and Cunningham J.R The physics of radiology 4th edition. Charles C. Thomas publisher. USA 18. Kalra MK, Maher MM, Toth TL, et al. Strategies for CT radiation dose optimization. Radiology 2004; 230: Lewis, M. (2005). Radiation dose issues in multi-slice CT scanning. ImPACT technology 20. Maria Lewis, 2005, : Radiation Dose Issue in Multi-Slice CT Scanning, ImPACT technology update no Michael, G. (2001). X-ray computed tomography. Physics Education, 36, Papp, Jeffrey, PhD,RT (R) (QM), 2006, Quality Management in The Imajing Sciences, third edition. 23. Seeram, E. (2009). Computed Tomography,Physical Principles, Clinical Application and Quality Control (third ed.). USA. IJIRAE , All Rights Reserved Page -54