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Quantification of the volumetric bone mineral density using the two-compartment model and computed tomography images

張貼者:2016年6月20日 上午12:28MEPIP MEPIP   [ Yan-Lin Liu 已於 2016年8月22日 上午12:43 更新 ]

骨質密度(bone mineral density, BMD)為診斷骨質疏鬆的重要指標,臨床上主要以DXA (dual-energy X-ray absorptiometry, DXA)為主要的量測方法,然而DXA掃描受到病人的體厚與檢查部位之限制,難以進行絕對BMD量化。

本研究使用TCMTwo Compartment Model, TCM)方法,搭配自製的K2HPO4骨等校假體以定量vBMD (volumetric BMD, vBMD),首先調配出0.135 0.533g/cm3K2HPO4水溶液,並進行電腦斷層儀掃描,以建立vBMDCT值關聯性,接著以標準周邊骨等校假體進行驗證,最後利用28CT髖部影像計算vBMD,並與DXA所求得的aBMD進行比對。

自製假體與標準周邊骨等校假體於不同四個部位的差異分別為, 20.4%13.3%10.3% 與 -1.8%,其平均骨盆的vBMD與aBMD分別為0.166±0.025 g/cm3 與0.892±0.130 g/cm2利用TCM方法所計算出來的vBMD與DXA取得的aBMD具有良好的線性關係,利用TCM方法可於各種CT掃描儀中快速進行骨質密度的定量,能有效改善骨質密度評估的準確性,進一步作為骨質疏鬆診斷的參考標準。




Simulation of breast compression in mammography using finite element analysis: a preliminary study

張貼者:2016年6月20日 上午12:25MEPIP MEPIP   [ 劉佩遠 已於 2016年8月22日 上午3:40 更新 ]

    在乳房攝影中,乳房的壓迫一直是很值得討論的議題,適當的壓迫不只可以提升影像品質,也可以降低劑量,因此本研究希望在真實壓迫前可以模擬乳房的壓迫情形並做乳房壓迫厚度或劑量的評估。

    本研究是利用有限元素分析的方式計算模型模擬3D乳房壓迫的狀況。在模擬模型的建立是依據MRI的影像,並模擬乳房攝影中的CC view壓迫方式,再利用Abaqus/CAE去模擬10-16daN下乳房壓迫的非線性彈性組織的變形。利用臨床上的MRI案例做壓迫模型,將真實乳房攝影CC view中的乳房壓迫厚度和在相同磅數的條件下做乳房壓迫模型的驗證。

    在乳房驗證的部分,模擬乳房壓迫的厚度差異,平均為3.1mm,而最大的差異為7.8mm。在10-16daN的模擬壓迫情況下,平均的乳房壓迫厚度分別為5.91, 5.21, 4.76, and 4.40 cm

    本研究主要是藉由MRI影像建立壓迫模型,並在未做乳房攝影前模擬真實的壓迫狀況,可以協助做個人化的乳房壓迫模型的建立,並進一步評估個人化的乳房壓迫厚度或平均乳腺劑量。




Small-Field Measurements of 3D Polymer Gel Dosimeters in Radiotherapy

張貼者:2016年6月19日 下午10:05MEPIP MEPIP   [ Tian-Yu Shih 已於 2016年8月22日 上午8:12 更新 ]

隨著治療儀器以及技術的進步,三維空間治療技術已普遍使用於放射治療,小型照野具明顯之劑量梯度變化,因此劑量準確度及劑量分布的驗證更顯重要。

本研究利用NIPAM聚合物凝膠劑量計測量不同照野大小的劑量分佈。凝膠劑量計由5%明膠,5%的單體,3%交聯劑,和5mM THPC組成。凝膠劑量計於接受輻射照射後2496小時,利用錐形束的光學計算斷層攝影(optical CT)掃描器被讀出。實驗結果將NIPAM凝膠劑量計測得的劑量分佈進行比較,並使用γ評估法分析與治療計劃系統的輸出差異。以通過率3/ 3毫米為標準,在× 5, 3 × 3, 2 × 2, 1 × 10.5 × 0.5平方厘米的照野合格率分別高達91.7 %,90.7 %,88.2 %,74.8 %和37.3 %。以5/ 5毫米的標準,γ評估法在× 5× 3,和× 2平方厘米通過率均超過99 %。

    由實驗結果可得知NIPAM凝膠劑量計搭配錐狀光學電腦斷層儀,具有良好之劑量再現性及劑量準確定,作為臨床劑量驗證工具具有極大潛力。


Evaluation of dose conversion coefficients for external exposure using taiwanese reference man and woman

張貼者:2016年6月19日 下午10:02MEPIP MEPIP

Reference man has been widely used for external and internal dose evaluation of radiation protection. The parameters of the mathematical model of organs suggested by the International Commission of Radiological Protection (ICRP) are adopted from the average data of Caucasians. However, the organ masses of Asians are significantly different from the data of Caucasians, leading to potentially dosimetric errors. In this study, a total of 40 volunteers whose heights and weights corresponded to the statistical average of Taiwanese adults were recruited. Magnetic resonance imaging was performed, and T2-weighted images were acquired. The Taiwanese reference man and woman were constructed according to the measured organ masses. The dose conversion coefficients (DCFs) for anterior–posterior (AP), posterior–anterior (PA), right lateral (RLAT) and left lateral (LLAT) irradiation geometries were simulated. For the Taiwanese reference man, the average differences of the DCFs compared with the results of ICRP-74 were 7.6, 5.1 and 11.1 % for 0.1, 1 and 10 MeV photons irradiated in the AP direction. The maximum difference reached 51.7 % for the testes irradiated by 10 MeV photons. The size of the trunk, the volume and the geometric position of organs can cause a significant impact on the DCFs for external exposure of radiation. The constructed Taiwanese reference man and woman can be used in radiation protection to increase the accuracy of dose evaluation for the Taiwanese population.


Image reconstruction of optical computed tomography by using the algebraic reconstruction technique for dose readouts of polymer gel dosimeters

張貼者:2016年6月19日 下午9:59MEPIP MEPIP

Optical computed tomography (optical CT) has been proven to be a useful tool for dose readouts of polymer gel dosimeters. In this study, the algebraic reconstruction technique (ART) for image reconstruction of gel dosimeters was used to improve the image quality of optical CT. Cylindrical phantoms filled with N-isopropyl-acrylamide polymer gels were irradiated using a medical linear accelerator. A circular dose distribution and a hexagonal dose distribution were produced by applying the VMAT technique and the six-field dose delivery, respectively. The phantoms were scanned using optical CT, and the images were reconstructed using the filtered back-projection (FBP) algorithm and the ART. For the circular dose distribution, the ART successfully reduced the ring artifacts and noise in the reconstructed image. For the hexagonal dose distribution, the ART reduced the hot spots at the entrances of the beams and increased the dose uniformity in the central region. Within 50% isodose line, the gamma pass rates for the 2 mm/3% criteria for the ART and FBP were 99.2% and 88.1%, respectively. The ART could be used for the reconstruction of optical CT images to improve image quality and provide accurate dose conversion for polymer gel dosimeters.


Optimization of Imaging Parameters for SPECT scans of [99mTc]TRODAT-1 Using Taguchi Analysis

張貼者:2016年6月19日 下午9:56MEPIP MEPIP

Parkinson’s disease (PD) is a neurodegenerative disease characterized by progressive loss of dopaminergic neurons in the basal ganglia. Single photon emission computed tomography (SPECT) scans using [99mTc]TRODAT-1 can image dopamine transporters and provide valuable diagnostic information of PD. In this study, we optimized the scanning parameters for [99mTc]TRODAT-1/SPECT using the Taguchi analysis to improve image quality. SPECT scans were performed on forty-five healthy volunteers according to an L9 orthogonal array. Three parameters were considered, including the injection activity, uptake duration, and acquisition time per projection. The signal-to-noise ratio (SNR) was calculated from the striatum/occipital activity ratio as an image quality index. Ten healthy subjects and fifteen PD patients were used to verify the optimal parameters. The estimated optimal parameters were 962 MBq for [99mTc]TRODAT-1 injection, 260 min for uptake duration, and 60 s/projection for data acquisition. The uptake duration and time per projection were the two dominant factors which had an F-value of 18.638 (38%) and 25.933 (53%), respectively. Strong cross interactions existed between the injection activity/uptake duration and injection activity/time per projection. Therefore, under the consideration of as low as reasonably achievable (ALARA) for radiation protection, we can decrease the injection activity to 740 MBq. The image quality remains almost the same for clinical applications.



A novel adaptive discrete cosine transform-domain filter for gap-inpainting of high resolution PET scanners

張貼者:2016年6月19日 下午9:53MEPIP MEPIP

Purpose: Several positron emission tomography (PET) scanners with special detector block arrangements have been developed in recent years to improve the resolution of PET images. However, the discontinuous detector blocks cause gaps in the sinogram. This study proposes an adaptive discrete cosine transform-based (aDCT) filter for gap-inpainting. Methods: The gap-corrupted sinogram was morphologically closed and subsequently converted to the DCT domain. A certain number of the largest coefficients in the DCT spectrum were identified to determine the low-frequency preservation region. The weighting factors for the remaining coefficients were determined by an exponential weighting function. The aDCT filter was constructed and applied to two digital phantoms and a simulated phantom introduced with various levels of noise. Results: For the Shepp-Logan head phantom, the aDCT filter filled the gaps effectively. For the Jaszczak phantom, no secondary artifacts were induced after aDCT filtering. The percent mean square error and mean structure similarity of the aDCT filter were superior to those of the DCT2 filter at all noise levels. For the simulated striatal dopamine innervation study, the aDCT filter recovered the shape of the striatum and restored the striatum to reference activity ratios to the ideal value. Conclusions: The proposed aDCT filter can recover the missing gap data in the sinogram and improve the image quality and quantitative accuracy of PET images. © 2014 American Association of Physicists in Medicine. [http://dx.doi.org/10.1118/1.4886035]


Performance Enhancement of a Web-Based Picture Archiving and Communication System Using Commercial Off-the-Shelf Server Clusters

張貼者:2016年6月19日 下午9:51MEPIP MEPIP

The rapid development of picture archiving and communication systems (PACSs) thoroughly changes the way of medical informatics communication and management. However, as the scale of a hospital’s operations increases, the large amount of digital images transferred in the network inevitably decreases system efficiency. In this study, a server cluster consisting of two server nodes was constructed. Network load balancing (NLB), distributed file system (DFS), and structured query language (SQL) duplication services were installed. A total of 1 to 16 workstations were used to transfer computed radiography (CR), computed tomography (CT), and magnetic resonance (MR) images simultaneously to simulate the clinical situation. The average transmission rate (ATR) was analyzed between the cluster and non cluster servers. In the download scenario, the ATRs of CR, CT, and MR images increased by 44.3%, 56.6%, and 100.9%, respectively, when using the server cluster, whereas the ATRs increased by 23.0%, 39.2%, and 24.9% in the upload scenario. In the mix scenario, the transmission performance increased by 45.2% when using eight computer units. The fault tolerance mechanisms of the server cluster maintained the system availability and image integrity.The server cluster can improve the transmission efficiency while maintaining high reliability and continuous availability in a healthcare environment.


A preliminary study of the thermal measurement with nMAG gel dosimeter by MRI

張貼者:2016年6月19日 下午9:47MEPIP MEPIP

The methacrylicacid (nMAG) gel dosimeter is an effective tool for 3-dimensional quality assurance of radiation therapy. In addition to radiation induced polymerization effects, the nMAG gel also responds to temperature variation....


Radiation dose evaluation of dental cone beam computed tomography using ananthropomorphic adult head phantom

張貼者:2016年6月19日 下午9:43MEPIP MEPIP   [ 已更新 2016年6月19日 下午9:48 ]

Dental cone beam computed tomography (CBCT) provides high-resolution tomographic images and has been gradually used in clinical practice. Thus, it is important to examine the amount of radiation dose resulting from dental CBCT examinations. In this study, we developed an in-house anthropomorphic adult head phantom to evaluate the level of effective dose.


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