Development of SCENARIA New Version Software MEDIX VOL. 62 P.32 P.35

Transcription

1 Development of SCENAIA New Version Software Takayuki Kadomura Toshio Sakamoto Kana Tanaka Takatsugu Ito Yuuko Nishimura Naomi Maekawa MEDIX VOL. 62 P.32 P.35

2 Development of SCENAIA New Version Software Takayuki Kadomura Toshio Sakamoto Kana Tanaka Takatsugu Ito Yuuko Nishimura Naomi Maekawa CT system Division, Hitachi Medical Corporation Since the launch of SCENAIA 1 in 21, we have been receiving various requests from users due to the changes in the environment surrounding medical fronts and the diversification of examinations. Especially the needs for low dose in CT systems have been increasing more than ever. In view of these circumstances, we have developed the SCENAIA new version software based on the concept of Dose eduction. In the SCENAIA new version software, features for dose reduction include IntelliEC 2 Plus that combines the noise reduction technique and AEC (Auto Exposure Control)technique, IntelliEC Cardiac that enables the tube current modulation responding to each cardiac phase in cardiac examination, and the function to manage dose information. With these features, SCENAIA new version software delivers the comprehensive cares for the radiation dose. Key Words: CT System, Low Dose, IntelliEC, Intelli IP, ECG 1. Introduction As Japanese market for multi-slice CT system has been progressing towards higher number of slices, the main market has shifted from 4-16slice CT to a slice CT market. High-tier systems of greater than 64slice CT are installed and used not only in university or local flagship hospitals, but also in medium-sized hospitals and local medical examination facilities. These institutions require the system that can perform examinations on various parts of the body, including cardiac examinations. Under the market trends, Hitachi has developed SCE- NAIA 1 -a whole-body X-ray CT system equipped with a 64slice detector that can perform a wide range of scan functions at a high-speed of.35 seconds. The system has been available commercially since 21 1). Considering the current healthcare environment, the percentage of elderly in the Japanese population reached 24.1% in the year 213 and is expected to keep increasing in the future 2), As the population ages, the number of CT examinations increases concurrently year by year 3), and there is a need for efficient examinations from the medical front. Additionally, in the wake of the Great East Japan Earthquake, the awareness of radiation exposure has been increasing, not only from healthcare workers but also from patients, leading to the ever-increasing need to lower the radiation dose used for diagnostic equipments. Under such a background, we developed SCENAIA new version software. The software is not only equipped with a dose reduction function but also a feature to manage radiation exposure, thus it can perform comprehensive care taking into account of radiation exposure. In this paper, we introduce validation results on the features related to dose reduction and dose management of this new version software.

3 Intelli IP Advanced Projection space Noise reduction processing based on a statistical model Back projection Image space Image quality tune based on an anatomical model Iteration Iteration Figure 1: Intelli IP Advanced Processing Overview 2. IntelliEC 2 Plus IntelliEC Plus is the advanced version of IntelliEC, an AEC (Auto Exposure Control)function that has been used in SCENAIA since the beginning of its production. Moreover, IntelliEC Plus can be used in combination with Intelli IP 3 Advanced, Hitachi s noise reduction function. Intelli IP Advanced is a technique that, after reducing noise in the projection space based on a high-precision statistical model via iterative processing, tunes image quality Input parameters when setting IntelliEC IP Advanced Target SD 1HU ma calculation 2mA Scan 1HU based on anatomical and statistical information in the image space (Figure 1) 4). In order to adapt to the various situations such as the different scanned regions or conditions, 7 levels of noise reduction rate were configured. IntelliEC Plus calculates the radiation dose to reach a target SD by taking account the noise reduction rate by Intelli IP Advanced. Figure 2 shows a comparison of image processing using IntelliEC and IntelliEC Plus. In the case where IntelliEC and Intelli IP Advanced are set independently as shown in Figure 2a, the noise reduction process of Intelli IP Advanced is performed after scan, resulting in a final image with a lower SD than the target SD. On the other hand, the ma calculation process in IntelliEC Plus is done based on the noise reduction rate by Intelli IP Advanced as shown in Figure 2b, therefore the final image attains the target SD theoretically. Figure 3 shows the evaluation results with phantom using IntelliEC Plus. Scan of abdominal area was performed with the following parameters: target SD: 11, rotation time:.35s, reconstruction filter: abdominal standard, and slice thickness: 1.25mm. In IntelliEC Plus, Intelli IP a: IntelliEC IP Advanced Image reconstruction Input parameters when setting IntelliEC Target SD ma calculation ma calculation based on Intelli IP Advanced 7HU 1HU 2mA 1mA Target SD: 11 IntelliEC Effective mas 155mAs Effective mas 113mAs IntelliEC Plus Scan 14HU b: IntelliEC Plus Image reconstruction 1HU SD11.12 IntelliEC SD1.95 IntelliEC Plus Figure 2: Processing overview of IntelliEC and IntelliEC Plus Figure 3: Evaluation result of IntelliEC Plus by phantom

4 Advanced Lv.3 was selected. Although the final results of SD value were both close to the target SD, the effective ma with IntelliEC and IntelliEC Plus were 155 and 113mAs, respectively, which means reduction in radiation dose is possible even while maintaining image quality. Compared to the method of which Intelli IP Advanced is not synchronized with IntelliEC, results obtained with IntelliEC Plus clearly show that the target SD can be achieved with ease, and it enables scan at a lower radiation dose; and thus, further dose reductions can be expected. image while at the same time reducing radiation exposure during the examination. Figures 5 and 6 show the results of tube current modulation using phantom. We determined the cardiac phase to expose high ma as 75% (the relative value of which the - interval is set as 1%), which is the mid-diastolic phase in case of 6-bpm, then confirmed the follow-up performance of dose modulation (low tube current: 2mA, high tube current: 7mA)with the actual values of tube current and image SD. As shown in Figure 5, the tube current began to increase from 55% and reached the set current value at 6% of the cardiac phase. The high tube cur- 3. IntelliEC Cardiac With the increase in detector width and scan speed of greater than 64slice CT system, it is now possible to perform imaging of a continuously moving heart by synchronizing CT with ECG. However, scan must be done at a very slow table pitch when compared to the volume scan, since it is necessary to collect raw data with the same cardiac phase by synchronizing ECG Moreover, because the heart rate of the patient also changes during scan, it is necessary that X-ray needs to be exposed continuously in order to obtain an image of diastolic and systolic phases simultaneously. Thus this increases the radiation risk. IntelliEC Cardiac is a function to modulate the tube current under retrospective scan based on the cardiac phase, which results in reduced radiation exposure during cardiac examinations. For patients with a slow heart rate, it is said that the optimal cardiac phase is at the mid-diastolic phase. Thus, as shown in Figure 4, by performing scan with high ma only at the mid-diastolic phase and performing scan with low ma at the other phases with more movement such as the systolic phase, it is possible to obtain an effective Figure 4: Overview of IntelliEC Cardiac 5 Cardiac phase Figure 5: IntelliEC Cardiac tube current modulation results Diastolic phase SD Figure 6: IntelliEC Cardiac SD change

5 rent value continued to 85% of cardiac phase, began to decrease, and then reached the low tube current value at 9% of cardiac phase. The reason why the tube current increased earlier than the set cardiac phase was in consideration of temporal resolution. Since the maximum temporal resolution in a retrospective scan is 2ms, it is necessary to have an interval of around 1ms before and after the 75% of cardiac phase in order to reach the set high tube current. In this case, it was necessary to perform the scan with high ma between 65% to 85% of the cardiac phase as the heart rate was 6bpm,. As a result, although the tube current reached the set high tube current value slightly earlier than expected, tube current modulation was able to be achieved as intended. Figure 6 shows the change in image SD in response to the changes in tube current. SD transition corresponding to the cardiac phase is inversely proportional to the tube current, and its follow-up performance based on tube current and image SD was noticeable. The results confirmed that image SD reached the minimum value at around 75% cardiac phase where the scan was done at the set high tube current value. Figure 7: Simple Dose eport Simple Dose eport Dose S IS PACS Another characteristic of this function is the ability which reflects the relationship between the patient s heart rate and optimum phase in order to set different high tube current values for the diastolic and systolic phases individually. This makes it possible to perform the dose modulation with a high degree of freedom in accordance with the patient s condition. 4. Simple Dose eport/dicom Dose S Other than the dose reduction techniques described so far, many kinds of other dose reduction functions have been introduced by various manufacturers. However, it should be noted that ineffective exposure is caused if the diagnosable image cannot be obtained, even if radiation exposure to the patients is lowered by using these techniques. It is important to achieve the optimal balance between radiation dose and image quality for producing reliable images that can be used for diagnosis. So what is the proper dose amount in a wide range of CT examinations? In order to clarify the answer to this question, a series of movements to study the proper dose for different types of examinations have been initiated internationally. From the above background, it is required for CT system to establish a mechanism to record the radiation dose easily and to be managed by CT users. In addition, in the United States, the FDA is now imposing the requirements on dose reduction and management function as standard features in all commercial CT systems. Since the different types of PACS systems or DICOM viewers are used in medical facilities, it is important to have the compatibility with those management systems. Simple Dose eport is a function that creates dose information caused by CT examinations as a secondary capture and send to PACS system in the same manner as image data (Figure 7). Dose information is stored in the image server, and confirmed easily together with the CT imageby using a PACS image viewer. Furthermore, DICOM Dose S (DICOM Dose Structured eport)is a function that can send dose information as a structured report to a PACS system by using DICOM standard which was officially standardized in 28. If the PACS system is compliant with DICOM Dose S, dose information collection and management can easily be achieved. Since Simple Dose eport and DICOM Dose S utilize DICOM, a common medical communication standard, it is possible to increase the compatibility with the existing equipments at a relatively low cost (Figure 8). Figure 8: Image of Simple Dose eport / DICOM Dose S

6 5. Conclusion New version software for SCENAIA was developed by focusing on dose reduction and dose management functions. However, radiation exposure has been the biggest challenge from the beginning of CT history and has been a never-ending topic for CT manufacturers.we would like to collect the voice of customers continuously and engage to further research and development in these areas. 1 SCENAIA, 2 IntelliEC, 3 Intelli IP are registered trademarks of Hitachi Medical Corporation. eferences 1) Tetsuo Nakazawa et al.: Sate-of-the-art technology of multi-slice CT SCENAIA. MEDIX, Vol.55: 45-48, ) Cabinet Office: White paper on the aging society 213 edition 3) Kanae Nishizawa et al.: Survey of CT Practice in Japan and Collective Effective Dose Estimation. Journal of Japan adiological Society, vol.64(3), , 24. 4) Taiga Goto et al.: Advanced Noise eduction Processing for X-ray CT System with Iterative Processing. MEDIX, Vol.56: 43-46, 212.