재구성 방법(점 확산함수 적용 유무)에 따른 PET/MR 영상 평가

박찬록,문일상,노경운,Park, Chan Rok,Moon, Il Sang,Noh, Gyeong Woon 대한핵의학기술학회 2018 핵의학 기술 Vol.22 No.1

NEMA IEC body phantom으로 PET/MR 스캐너를 이용해 MR 영상 기반의 감쇠보정 된 PET 영상을 얻고, 반복재구성 기반의 점 확산 함수(PSF)에 적용 유무에 따라 PET 영상을 Contrast recovery 와 SNR 의 평가 인자를 적용해 평가하였다. 또한, 동일한 재구성 방법에 따라 본원의 내원한 환자의 영상도 평가하였다. 데이터는 임상환자 와 팬텀 실험 모두 PSF를 적용해 재구성한 영상이 모두 영상의 질이 향상됨을 확인하였다. MR 기반으로 얻어진 PET 영상 평가가 추후에도 계속해서 필요하다고 사료된다. Purpose In this study, we evaluated image by applying with and without point spread function algorithm(PSF) according to reconstruction type. Materials and Methods Biograph mMR (Siemens, Germany) was used as PET/MR scanner. For phantom study, we used NEMA IEC Body phantom maintaining radioactivity ratio (hotsphere:background = 8:1). To evaluate phantom image quality, percent contrast recovery and signal to noise ratio (SNR) were used by drawing ROI to 4 spheres. In clinical study, the 20 patients who underwent simultaneous PET/MR was selected and set the ROI at liver. we evaluated images as SNR. Results In the phantom results, The percent contrast recovery applying PSF algoritm was high 5 % compared to without PSF algoritm and SNR was also high 11 %. In the clinical study result, we confirmed that The SNR applying PSF algoritm was high 5 % compared to without PSF algoritm. Conclusion We need to simulate a lot of phantom study and clinical analysis to improve image quality for PET/MRI.

Median modified wiener filter for improving the image quality of gamma camera images

박찬록,강성현,이영진 한국원자력학회 2020 Nuclear Engineering and Technology Vol.52 No.10

The filter technique was applied to noise images, as noise is the significant factor that cause poor image quality due to lower photon counting. The purpose of this study is to confirm that image quality can be improved using the median modified Wiener filter (MMWF) technique; this is achieved via a National Electrical Manufacturers Association International Electrotechnical Commission body phantom with four large spheres that are filled with the 99mTc radioisotope when evaluating the image quality. Conventional filters such as Wiener, Gaussian, and median filters were designed, and signal to noise ratio, coefficient of variation, and contrast to noise ratio were used as the evaluation parameters. The improvement in the image quality was in the following order, from the least to the highest improvement, in all cases: Wiener filter, Gaussian filter, median filter, and the MMWF technique. The results show that the image quality was improved from 20.6 to 65.5%, 7.4–40.3%, and 12.7–44.7% for the SNR, COV, and CNR values, respectively, when using the MMWF technique, compared with the use of conventional filters. In conclusion, our results demonstrated that the MMWF technique is useful for reducing the noise distribution in gamma camera images.

MR/PET을 이용한 UTE MR 펄스 시퀀스 기반 팬텀 내 주입물질에 따른 PET 영상 화질 평가

박찬록,이영진 대한자기공명기술학회 2022 대한자기공명기술학회지 Vol.32 No.1

Hybrid systems are widely used in the clinical field. One hybrid system employed is magnetic (MR)/positron emission tomography (PET), which is required for the simultaneous acquisition of anatomic and function information. Water is injected into material to fabricate the MR/PET phantom. However, water has lower permittivity and causes artifacts when acquiring the MR signal. Thus, the alternative material must acquire both the MR and PET signals in the phantom. Additionally, the attenuation correction technique, which can improve PET image quality, is applied to an ultrashort TE (UTE) MR pulse sequence. Hence, this study evaluated attenuation-corrected PET image quality according to injected material such as NaCl and NaCl + NiSO4 by acquiring the UTE MR pulse sequence. For the quantitative analysis, contrast recovery (CR), signal-to-noise ratio (SNR), and coefficient of variation (COV) were used. According to the results, the PET image quality with a UTE MR pulse sequence injected into NaCl material for CR, SNR, and COV was better by 1.38, 1.18, and 1.18 times than t hat for NaCl + N iSO4 m aterial with a UTE MR pulse sequence. We confirmed the compatibility of t he MR and PET signals using the MR/PET phantom. 자기공명영상장치(magnetic resonance, MR)/양전자 방출 단층촬영 장치(positron emission tomography, PET)는 두 가지 의료장치가 결합한 하이브리드 시스템으로써 MR의 해부학적 정보와 PET의 기능적 정보를 동시에 획득할 수 있는 최신 의료장치이다. 일반적으로 MR/PET의 우수한 팬텀 영상의 질 획득과 평가를 위하여 팬텀 내에 전기전도도가 낮은 액체 물질과 방사성동위원소를 주입하고, UTE MR 펄스 시퀀스를 적용한 감쇠 보정된 PET 영상을 획득한다. 본 연구의 목적은 MR/PET 전용 팬텀에서 물 대체물질로써 NaCl과 NaCl+NiSO4 물질에 따른 UTE MR 펄스 시퀀스를 획득하고, 감쇠 보정된 PET 영상의 질을 평가하고자 한다. 정량적 분석을 위하여 대조도 회복비(contrast recovery, CR), 신호대잡음비(signal to noise ratio, SNR), 변동 계수(coefficient of variation, COV)를 적용하였다. NaCl 물질 기반 UTE MR 펄스 시퀀스를 적용한 PET 영상의 질이 CR은 1.38배, SNR은 1.18배가 증가하였고, COV는 1.18배 감소함을 확인할 수 있었다. 결론적으로, MR/PET 전용 팬텀을 활용한 신호의 획득 가능성을 확인하였고, UTE MR 펄스 시퀀스는 해부학적 정보와 PET 영상의 질 향상에 필수적임을 확인할 수 있었다.

방광 팬텀 제작을 통한 충만여부에 따른 방광 주변 병변에 대한 영상 평가

박찬록,김재일,이홍재,김진의,Park, Chan-Rok,Kim, Jae-Il,Lee, Hong-Jae,Kim, Jin-Eui 대한핵의학기술학회 2016 핵의학 기술 Vol.20 No.1

방광 주변에 병변이 있는 환자의 경우 소변의 충만으로 방광 주변에 병변 평가의 영향이 있기 때문에 방광 팬텀을 직접 제작하여 방광 충만 여부에 따라 주변 병변이 미치는 영향을 평가하고자 한다. Biograph mCT40 (siemens, germany)을 사용하여 6개의 insert에 각각 14.8 MBq ($400{\mu}Ci$), Background 110 MBq (3 mCi), 방광에 74 MBq (2 mCi)를 주입하였다. NEMA IEC body 팬텀을 이용하여 고무풍선을 방광으로 대체하고 6개의 insert를 방광 주변 병변으로 설정하고, %BV, SUV, peak count rate의 영상평가 인자를 이용하여 비교하였다. % BV는 방광으로부터 거리가 멀수록 감소하는 것을 확인하였다. 방광으로부터 거리에 따른 hot sphere는 방광의 충만여부에 따라 $7.8{\pm}3.8%$의 SUV 차이가 났다. 방광으로부터의 거리가 0.4 cm 이하까지 방광을 비웠을 경우 평균 카운트가 약 14% 높게 측정되었으며, true count는 38% 감소한 반면, single count는 44%, random count는 61% 감소하였다. 그리고 그 이상의 거리에서는 큰 변화를 보이지 않았다. 그러므로 방광에 찬 소변이 주변 병변에 영향을 미치는 것을 확인하였고, 방광으로부터 거리가 가까울수록 영향이 크다는 것을 확인하였다. 방광이나 방광 주변에 병변이 있는 환자뿐만 아니라 PET-CT 검사를 하는 모든 환자에 있어 방광을 비우고 검사를 하는 것이 정확한 검사를 하는데 도움을 제공해 줄 것으로 사료된다. Purpose In this study, we evaluated image quality of lesion in the vicinity according filling and empty bladder developing bladder phantom. Materials and Methods Bladder phantom was developed by modifying NEMA IEC body phantom. Air-balloon was described as bladder and 6 insert were set as lesion in the vicinity bladder according to distance. The images were evaluated in terms of % BV, comparison of SUV and peak count rate (Single, Random and True count). Results % BV was decreased far away from bladder. There were different for SUV about $7.8{\pm}3.8%$ between filling and empty bladder. True count rate was decreased about 38 %. Single and random count were increased about 44, 61%. Conclusion When the lesion is close to bladder, noise is increased. That's why prior to PET-CT scan, It is important to urinate. and It helps patient to get the accurate result.

물리적 보정된 핵의학 영상 평가 : 정규화 보정

박찬록,윤석환,이홍재,김진의,Park, Chan Rok,Yoon, Seok Hwan,Lee, Hong Jae,Kim, Jin Eui 대한핵의학기술학회 2017 핵의학 기술 Vol.21 No.1

QA 과정을 통해 30개의 정규화 보정값을 얻고, 1개의 기준 데이터 설정 후 29개의 정규화 보정값과 비교하였다. 또한 각 정규화 보정값을 PET raw data 에 적용시켜 재구성된 영상을 동일한 ROI를 그려 SUV 와 count 로 비교평가 하였다. 30개의 정규화 보정값은 차이가 발생하지 않았으며, 각각의 정규화 보정값을 적용시킨 PET 영상도 크게 차이가 없었다. 핵의학 영상은 정량분석을 위해 불감시간 보정 및 광자의 감쇠 및 산란 등 물리적 현상에 대한 보정이 필요하고, 정규화 보정 또한 무시할 수 없는 보정 과정이다. 따라서 이런 과정을 통해 PET 장비의 균일성이 유지되고 여러 디텍터의 효율도 균등해야 영상의 왜곡을 방지할 수 있고, 질 좋은 영상을 만드는데 꼭 필요한 과정이므로 매일 QA 과정이 필요하다고 사료된다. Purpose In this study, we evaluated image by applying normalization factor during 30 days to the PET images. Materials and Methods Normalization factor was acquired during 30 days. We compared with 30 normalization factors. We selected 3 clinical case (PNS study). We applied for normalization factor to PET raw data and evaluated SUV and count (kBq/ml) by drawing ROI to liver and lesion. Results There is no significant difference normalization factor. SUV and count are not different for PET image according to normalization factor. Conclusion We can get a lot of information doing the quality assurance such as performance of sinogram and detector. That's why we need to do quality assurance daily.

Feasibility study of improved median filtering in PET/MR fusion images with parallel imaging using generalized autocalibrating partially parallel acquisition

박찬록,김재영,안창현,이영진 한국원자력학회 2023 Nuclear Engineering and Technology Vol.55 No.1

This study aimed to analyze the applicability of the improved median filter in positron emission tomography (PET)/magnetic resonance (MR) fusion images based on parallel imaging using generalized autocalibrating partially parallel acquisition (GRAPPA). In this study, a PET/MR fusion imaging system based on a 3.0T magnetic field and 18F radioisotope were used. An improved median filter that can set a mask of the median value more efficiently than before was modeled and applied to the acquired image. As quantitative evaluation parameters of the noise level, the contrast to noise ratio (CNR) and coefficient of variation (COV) were calculated. Additionally, no-reference-based evaluation parameters were used to analyze the overall image quality. We confirmed that the CNR and COV values of the PET/MR fusion images to which the improved median filter was applied improved by approximately 3.32 and 2.19 times on average, respectively, compared to the noisy image. In addition, the no-reference-based evaluation results showed a similar trend for the noise-level results. In conclusion, we demonstrated that it can be supplemented by using an improved median filter, which suggests the problem of image quality degradation of PET/MR fusion images that shortens scan time using GRAPPA.

Fast non-local means noise reduction algorithm with acceleration function for improvement of image quality in gamma camera system: a phantom study

박찬록,이영진 한국원자력학회 2019 Nuclear Engineering and Technology Vol.51 No.3

Gamma-ray images generally suffer from a lot of noise because of low photon detection in the gammacamera system. The purpose of this study is to improve the image quality in gamma-ray images using agamma camera system with a fast nonlocal means (FNLM) noise reduction algorithm with an accelerationfunction. The designed FNLM algorithm is based on local region considerations, including theEuclidean distance in the gamma-ray image and use of the encoded information. To evaluate the noisecharacteristics, the normalized noise power spectrum (NNPS), contrast-to-noise ratio (CNR), and coefficientof variation (COV) were used. According to the NNPS result, the lowest values can be obtainedusing the FNLM noise reduction algorithm. In addition, when the conventional methods and the FNLMnoise reduction algorithm were compared, the average CNR and COV using the proposed algorithm wereapproximately 2.23 and 7.95 times better than those of the noisy image, respectively. In particular, theimage-processing time of the FNLM noise reduction algorithm can achieve the fastest time comparedwith conventional noise reduction methods. The results of the image qualities related to noise characteristicsdemonstrated the superiority of the proposed FNLM noise reduction algorithm in a gammacamera system.

Nonvolatile Memory Characteristics Induced in High-k Dielectric Thin Films through Electron Irradiation

박찬록,이홍경,황진하,한영환,이병철,안기석 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.22

The current research aims to develop a simplified fabrication procedure for a nano-floating gate memory by using electron beam irradiation. The main strategy is to combine nanoscale highk dielectric thin films with highly accelerated electron beams, unlike the conventional approach involving multicomponent nanolaminates with dissimilar materials. This work investigated Al_2O_3 as a high-k dielectric thin film for testing the electron irradiation on high-k thin film materials. The Al_2O_3 thin films exhibited highly superior memory characteristics compared to those of the preexisting nano-floating gate memories into which charge-trapped components were incorporated for robust high-k dielectrics. The optimized Al_2O_3 thin films exhibited long-lasting retention features; approximately 75% of the programming information was maintained compared to that of the initial setting value, and the erase information did not change over time. Furthermore, the irradiated Al_2O_3 thin films exhibited the highest trap density of 7 × 10^(12) traps/cm^2.

Comparison of PET image quality using simultaneous PET/MR by attenuation correction with various MR pulse sequences

박찬록,이영진 한국원자력학회 2019 Nuclear Engineering and Technology Vol.51 No.6

Positron emission tomography (PET)/magnetic resonance (MR) scanning has the advantage of lessadditional exposure to radiation than does PET/computed tomography (CT). In particular, MR basedattenuation correction (MR AC) can greatly affect the image quality of PET and is frequently obtainedusing various MR sequences. Thus, the purpose of the current study was to quantitatively compare theimage quality between MR non-AC (MR NAC) and MR AC in PET images with three MR sequences. Percent image uniformity (PIU), percent contrast recovery (PCR), and percent background variability(PBV) were estimated to evaluate the quality of PET images with MR AC. Based on the results of PIU, 15.2%increase in the average quality was observed for PET images with MR AC than for PET images with MRNAC. In addition, 28.6% and 71.1% improvement in the average results of PCR and PBV respectively, wasobserved for PET images with MR AC compared with that with MR NAC. Moreover, no significant differencewas observed among the average values using three MR sequences. In conclusion, the currentstudy demonstrated that PET with MR AC improved the image quality and can be help diagnosis in all MRsequence cases.

소아 SPECT/CT 검사를 위한 최저조건에서의 피폭선량측정 및 팬텀의 영상평가

박찬록,최진욱,조성욱,김진의,Park, Chan Rok,Choi, Jin Wook,Cho, Seong Wook,Kim, Jin Eui 대한핵의학기술학회 2014 핵의학 기술 Vol.18 No.1

SPECT/CT로 소아 복부를 검사 하는데 있어 저선량 CT 조건에 따른 흡수선량을 측정하고 SPECT와 CT 영상의 질을 평가하고, 우수한 영상의 질을 유지하면서 최저의 흡수 선량을 받을 수 있는 tube voltage (kVp)와 tube current (mA)의 설정 방향을 알아보는데 목적을 두었다. 장비는 Discovery NM/CT 670을 사용하였다. PMMA phatom을 이용하여 80, 100 kVp 10, 15, 20, 25 mA의 조건을 설정하여 중심방향과 주변방향(3, 6, 9, 12시 방향의 평균) 의 흡수선량을 측정하였고, 그에 따른 image를 SNRD로 평가 하였다. CT QA performance phantom으로 CT image의 resolution을 MTF로 나타내었고, jaszczak phantom을 hot sphere와 배후방사의 비를 $^{99}mTc$을 1:8로 주입하여 4개의 sphere에 대한 SPECT image를 CNR로 평가하였다. 선량측정에서는 주변방향의 선량이 중심방향 선량보다 평균 7% 높게 측정되었으며, SNRD는 조건에 따라 유의한 차이가 없었으며 Resolution 평가에서는 0.385 lp/mm 기준으로 100 kVp가 80 kVp보다 평균 12% 재현성이 우수하였으며, jaszczak phantom을 이용해서 CT를 기반으로 한 attenuation correction 된 SPECT image를 CNR로 평가한 결과 CT조건의 변화와 무관하게 4개의 sphere 모두 유의한 차이를 보이지 않았다. 본 연구는 SPECT/CT 검사에서 최저의 흡수선량을 유지하고 우수한 영상의 질을 획득하는데 추가적인 연구가 필요할 것으로 사료된다. Purpose: The purpose of study was to evaluate radiation dose for pediatric patients by changing tube voltage (kVp) and tube current (mA) at minimum conditions. By evaluating radiation dose, we want to provide dose reduction for pediatric patients and maintain good quality of SPECT/CT images. Materials and Methods: Discovery NM/CT 670 Scanne was used as SPECT/CT. Tube voltages are 80 and 100 kvP. Tube currents are 10, 15, 20, 25 mA. Using PMMA (Polymethyl methacrylate) Phantom, radiation dose which were calculated at center and peripheral dose and SNRD (Signal to Noise Ratio Dose) were evaluated. Using the CT performance phantom, spatial resolution was evaluated as the MTF (Modulation Transfer Function) graph. Jaszczak phantom was used for SPECT image evaluation by CNR (Contrast to Noise to Ratio). Results: Radiation dose using the PMMA phantom was higher peripheral dose than center dose about 7%. SNRD were 7.8, 8.2, 8.3, 8.8, 8.8, 9.9, 9.8, 9.6 for 80 kVp 10, 15, 20, 25 mA, 100 kVp 10, 15, 20, 25 mA. We can distinguish 35, 45, 70, 71, 52, 58, 90, 110 linepair for 80 kVp 10, 15, 20, 25 mA, 100 kVp 10, 15, 20, 25 mA at resolution with MTF. CNR of SPECT images using CT attenuation map were 57.8, 57.7, 57.1, 56.7, 56.6, 56.7, 56.7, 56.7% for 80 kVp 10, 15, 20, 25 mA, 100 kVp 10, 15, 20, 25 mA. Conclusion: In this study, radiation dose for pediatric patients showed decreased low dose condition. And SNRD value was similar in all condition. Resolution showed higher value at 100kVp than 80kVp. for CNR, there was no significant difference. we should take additional study to prove better quality and dose reduction.