Clinical Experience Using the Open Bore Multislice CT System Supria (16 slice CT) MEDIX VOL. 61 P.8 P.11

Transcription

1 Clinical Experience Using the Open Bore Multislice CT System Supria (16 slice CT) Hiroki Kadoya Yukiko Kitagawa MEDIX VOL. 61 P.8 P.11

2 Clinical Experience Using the Open Bore Multislice CT System Supria (16 slice CT) Hiroki Kadoya Yukiko Kitagawa Kitagawa Hospital, Kouyuukai Medical Corporation (Hirado City, Nagasaki Prefecture) Clinical experience using the Supria 1 multislice (16 slice)ct system, manufactured by Hitachi Medical Corporation, introduced at our institution in March, 2014 is reported below. Supria enables smooth and efficient operations and settings to meet various scanning and patient positioning needs with its wide-open 750mm gantry bore and full data retention at the maximum FOV (500mmφ). Also, this CT system is capable of low exposure scanning, applying iterative reconstruction technology as a standard function. Furthermore, it realizes both the fast speed and wide range acquisition of thin slice volume data for short-time and high-resolution imaging. Key Words: Supria, FOV, Open Bore Gantry, Intelli IP 1. Introduction Our hospital, which opened in Hirado, Nagasaki, in 1954, currently has 52 beds. It has specialized departments in internal medicine, surgery, pediatrics, gastrointestinal medicine, cardiovascular medicine, proctology, radiology, and rehabilitation. As time had come to renew our CT system (Multislice CT ROBUSTO, Hitachi Medical Corporation), we decided to install a new system. In Hirado, Nagaski, the proportion of 65 years old or older is relatively high at 33.2% 1). Our hospital also has a geriatric health services facility in addition to a pediatrics department. Therefore, in selecting the device, we mainly considered the convenience of scan positioning, a reduced rate of rescanning for patients in a hunched position, and dose-reduction technology. Space and power requirements comparable to those of a conventional CT system additionally emerged as selection criteria, and therefore the decision was made in March 2014 to install the Supria 1 CT system, manufactured by Hitachi Medical Corporation (Fig. 1). Here, we report on our experiences using this CT system and present actual clinical images. Fig. 1: Supria

3 2. Outline of the installed system Supria has a minimum scan time of 0.75s/rot and is equipped with a 5MHU X-ray tube. It has a large gantry bore of 750mm. Regardless of the field of view (hereinafter referred to as FOV)which is set when planning the scan conditions, the system constantly retains all data at the maximum FOV (500mm). Given the frequent scanning of the elderly at our hospital, we judged that the system would contribute to reducing the rescanning rate. Furthermore, with regard to the scanning of children, we judged that use of the system would help to reduce their fear of examination. The system has a footswitch, which can control the movement of patient table based on the preset positions. This ensures safety by freeing up both hands of the operator while also enabling smooth positioning of the patient. The system is also equipped with a Breath guide-a useful function for elderly patients that allows breath-holding instructions to be displayed with characters. This function is implemented by miniature monitors, placed at 3 sites within the gantry. As for functions related to dose reduction, the system is equipped with IntelliEC 2, which forms an elliptical model of the human body for each patient to control the tube current, and Intelli IP 3, an image processing technique that applies iterative reconstruction which repeats the calculations to reduce the noise both in projection space and image space. We intend to reduce radiation exposure by utilizing these functions not only when scanning children but during all examinations. 3. Presentation of clinical images (1)Clinical case 1 Brain image of a child: 6-year old boy Scanning was performed with the protocol shown in Table 1. For scanning unsedated children, the scan time must be shortened. Although we considered performing a non-helical scan by increasing the rotation speed to 0.75s/ rot since Supria installed here could generate outputs of up to 400mA, we employed the scan conditions in Table 1 in consideration of the tradeoff with the view rate. The brain image of a child generally shows less contrast than that of an adult. However, the contrast obtained in this case (Fig. 2)is likely to be sufficient for making clinical diagnoses. In addition, we consider that by jointly using Intelli IP, it improves the image characteristics such as graininess, and this leads to obtaining the images which are easy to diagnose. For Intelli IP, the operator can select from among seven levels (Level 1 to Level 7). We confirmed how noise varied at each level by using a water phantom. Figure 3 shows the results for the rate of noise reduction measured using the water phantom. In the case of scanning conditions that assumed a pediatric brain scan, we confirmed that the noise-reduction effect increased by 7.7% on average for each increment in Intelli IP level. Table 1: Scanning conditions for Clinical case 1 Fig. 2: Brain image of a child: 6-year old boy SD value Normal Slice thickness Collimation Tilt Kernel F19 FBP Level 1 Level 2 Level 3 Level 4 Level 5 Level 6 Level 7 Intelli IP level 100mAs 200mAs 240mAs 250mAs 300mAs 350mAs 400mAs Fig. 3: Noise reduction effect of Intelli IP using a water phantom Figure 4 shows images in which Intelli IP was applied to pediatric brain scans. The scanning conditions are identical to those indicated in Table 1. We studied whether images with better visibility could be obtained owing to the noise-reduction effect by increasing the level of Intelli IP, even with actual clinical images. As a result of performing SD measurements for each case at the epiphysis level, it was confirmed that SD reduction effect is similar to that of the phantom experiment. However, when the level is increased excessively, our impression is that the images become unsuitable for diagnostic use. In the case

4 of the current pediatric brain scan conditions, we infer that Level 2 or Level 3 is approximately the appropriate level. Table 2. Because Supria constantly retains all data at the maximum FOV (500mm), it can restore the lost portion only by recalculation and can re-center the image (Fig. 5b). When scanning is performed with a fixed tube current, this reduces radiation exposure by approximately 69mGy per rotation compared to when rescanning is performed. FBP Level 1 Table 2: Scanning conditions for Clinical case Normal Slice thickness Collimation Tilt Kernel F12 Level 2 Level 3 a: Image loss example Level 4 Level 5 b: Re-calculation example Fig. 5: Brain image of patient with a hunched condition: 86-year old male Level 6 Level 7 Fig. 4: Example of Intelli IP applied to the brain of a child: 9-year old boy (2)Clinical case 2 Brain image of patient with a hunched condition: 86-year old male In scanning patients who are hunched, image loss may occur when the patient deviates from the FOV set at the time of scanning. Figure 5a shows an image in which a defect occurred under the scanning conditions shown in (3)Clinical case 3 Adult lung image (arms lowered): 92-year old female At our hospital, scanning with the arms lifted is difficult in some cases (e.g., with elderly patients). Figure 6 shows an image of the lungs (arms lowered)scanned under the conditions shown in Table 3. The image suggests that artifacts such as those that arise from the upper forelimb bone are reduced to a degree that is unproblematic for diagnosis. This is presumably due to the effect of the CORE technique for the newly installed 3D image reconstruction algorithm, in addition to the effects of ADNR (Automatic Data Noise Reduction), an artifact suppression software program that had also been installed in the previous system.

5 Table 3: Scanning conditions for Clinical case mA 0.75 Volume Slice thickness Collimation Beam pitch Kernel F22/F32 However, increasing the level of Intelli IP appears to change the visual quality. Specifically, image blurring tends to intensify in accordance with the level of Intelli IP, as shown in Fig. 4. This suggests that when considering the compatibility between dose reduction and image quality, the proper level of Intelli IP and scanning conditions should be continuously explored and established in accordance with conditions such as age, sex, and scanned area of the patient. Although here we primarily investigated dose reduction in children, it will be important to continue investigations on optimizing scanning conditions (including Intelli IP)so that radiation exposure can also be reduced during other CT examinations. Fig. 6: Adult lung image arms lowered : 92-year old female (4)Clinical case 4 Adult lung image (patient with difficulty assuming a dorsal position): 86-year old male When scanning elderly patients, we sometimes encounter those that have difficulty assuming the dorsal position, similar to cases of scanning with the arms lowered. Figure 7 shows an image obtained by scanning in the dorsal position. For Supria installed here, which has a large gantry bore of 750mm, the positioning of patients that need to be scanned in an irregular position is relatively easy. In addition, our impression is that artifacts occur infrequently even during scanning in an irregular position. 5. Summary Supria, manufactured by Hitachi Medical Corporation and installed in our hospital, has a high degree of freedom with regard to scan positioning during examination due to its large gantry bore and constant retention of data within the maximum FOV. In addition, because examinations with a reduced dose are possible, we confirmed that the system fits well with the classes of patient and regional characteristics of our hospital and has high clinical utility. High-resolution images can also be obtained even as the breath holding time is shortened. This allows high-resolution images and low-dose examinations to be achieved simultaneously-a feat that was difficult to achieve with the previous system. We suggest that this system can contribute to improving the quality of examinations (e.g., image quality)and providing further benefits for patients. 1 Supria, 2 IntelliEC, and 3 Intelli IP are registered trademarks of Hitachi Medical Corporation. Fig. 7: Adult lung image patient with difficulty assuming the dorsal position : 86-year old male 4. Future challenges At our hospital, we consider it necessary to implement further dose-reduction measures, particularly when scanning children. As has already been reported, when viewed in terms of image SD values, a maximum dose-reduction effect of approximately 80% can be expected by using Intelli IP 2). References 1) 2010 Population Census, Statistical Tables According to Prefecture, City, District, Town, and Village. (in Japanese) 2) K. Uchiyama et al.: Background Introduction and Usage Experience of MDCT Supria from Hitachi Medical Corporation. Radfan, Vol.11, No.15: 32-35, (in Japanese)