Fiber direction estimation using constrained spherical deconvolution based on multi-model response function / 生物医学工程学杂志

Constrained spherical deconvolution can quantify white matter fiber orientation distribution information from diffusion magnetic resonance imaging data. But this method is only applicable to single shell diffusion magnetic resonance imaging data and will provide wrong fiber orientation information in white matter tissue which contains isotropic diffusion signals. To solve these problems, this paper proposes a constrained spherical deconvolution method based on multi-model response function. Multi-shell data can improve the stability of fiber orientation, and multi-model response function can attenuate isotropic diffusion signals in white matter, providing more accurate fiber orientation information. Synthetic data and real brain data from public database were used to verify the effectiveness of this algorithm. The results demonstrate that the proposed algorithm can attenuate isotropic diffusion signals in white matter and overcome the influence of partial volume effect on fiber direction estimation, thus estimate fiber direction more accurately. The reconstructed fiber direction distribution is stable, the false peaks are less, and the recognition ability of cross fiber is stronger, which lays a foundation for the further research of fiber bundle tracking technology.

Quantitative Variation of Time-Activity Curve Derived Parameters with Regional Variation of Background Region of Interest, in Salivary Scintigraphy: A Retrospective Comparative Evaluation

Aim and Objective: Quantitative analysis of time-activity curve (TAC) derived from 99mTc-pertechnetate salivary glandscintigraphy, used in the evaluation of salivary gland function, is almost always corrected for background count. The objectiveof this study was to: (a) Examine the effect of the alteration of anatomical position of the background region of interest (ROI) onthe (1) semi-quantitative parameters, i.e., upslope (Us) and stimulated downslope (Ds), derived from TAC and (2) on minimumand maximum pixel counts of pixel histogram of background ROI. (b) Examine the effect of minimum and the maximum pixelcounts of the background ROI on the values of Us and Ds.Materials and Methods: In this retrospective study, 16 patients were included who had undergone 99mTc-pertechnetatesalivary scintigraphy for various reasons but had normal salivary scintigraphy reports. Three different sets of background indifferent anatomical positions were chosen: (i) A pair of supraclavicular background ROI, (ii) an isolated central rectangularbackground ROI in brain, and (iii) an isolated suprathyroid ROI. We then calculated two important semi quantitative parameters,i.e., Us and Ds from the TAC of the salivary glands. Individual TAC was generated against each set of the above-mentionedbackgrounds. Individual pixel histogram was also generated against each TAC. Minimum and maximum pixel count of thegenerated background pixel histograms was identified. Comparative studies were made among the afore-mentioned variables.Results and Conclusion: The values of Us and Ds derived from respective background corrected TAC matched well amongeach other irrespective of the altered anatomical positions of the background ROI. The minimum pixel counts per second (CPS)of the background pixel histogram varied with the change in anatomical position of the background ROI but it did not affect thevalues of Us and Ds. In contrast, the maximum pixel CPS of the background pixel histogram varied inversely with the valuesof Ds, although the value of Ds, showed no variation with the change in position of the background ROI.

Spiral scanning imaging and quantitative calculation of the 3-dimensional screw-shaped bone-implant interface on micro-computed tomography

PURPOSE: Bone-to-implant contact (BIC) is difficult to measure on micro-computed tomography (CT) because of artifacts that hinder accurate differentiation of the bone and implant. This study presents an advanced algorithm for measuring BIC in micro-CT acquisitions using a spiral scanning technique, with improved differentiation of bone and implant materials. METHODS: Five sandblasted, large-grit, acid-etched implants were used. Three implants were subjected to surface analysis, and 2 were inserted into a New Zealand white rabbit, with each tibia receiving 1 implant. The rabbit was sacrificed after 28 days. The en bloc specimens were subjected to spiral (SkyScan 1275, Bruker) and round (SkyScan 1172, SkyScan 1275) micro-CT scanning to evaluate differences in the images resulting from the different scanning techniques. The partial volume effect (PVE) was optimized as much as possible. BIC was measured with both round and spiral scanning on the SkyScan 1275, and the results were compared. RESULTS: Compared with the round micro-CT scanning, the spiral scanning showed much clearer images. In addition, the PVE was optimized, which allowed accurate BIC measurements to be made. Round scanning on the SkyScan 1275 resulted in higher BIC measurements than spiral scanning on the same machine; however, the higher measurements on round scanning were confirmed to be false, and were found to be the result of artifacts in the void, rather than bone. CONCLUSIONS: The results of this study indicate that spiral scanning can reduce metal artifacts, thereby allowing clear differentiation of bone and implant. Moreover, the PVE, which is a factor that inevitably hinders accurate BIC measurements, was optimized through an advanced algorithm.

Impact of Partial Volume Effect on Quantitative Results in SPECT/CT / 中国医学影像学杂志

Purpose The partial volume effect is a main factor to impact the image quality and the accuracy of the quantitative analysis of nuclear medicine image.The aim of this study is to evaluate the effects of partial volume effect on quantitative result in SPECT/CT.Materials and Methods A Jaszczak cylindrical phantom and IEC body phantom were performed with routine SPECT/CT imaging using CT attenuation correction,scatter correction and three-dimensional ordered subset expectation maximization (3D-OSEM) reconstruct image.The system volume sensitivity (cpm/kBq) were acquired from the reconstructed image of Jaszczak phantom study.The absolute activity concentration (kBq /ml) of the hot sphere was calculated according to the IEC phantom study that the intensity of radioactivity had been measured in the dose calibrator,then checking computations the quantitative accuracy of all.The difference of quantitative accuracies from the different volume hot sphere was compared tusing a given acquisition and reconstruction parameter.The effects of volume of interest (VOI),target-to-background ratio (TBR) and acquisition time on quantitative accuracy were evaluated.Results CT attenuation correction and scatter correction,the difference of absolute activity and true activity value was obviously correlation with the sphere size by using 3D-OSEM.The quantitative errors were decreased along with the increased of sphere size (r=-0.844,P＜0.05).The quantitative accuracy were significantly affected by the VOI size in the 1.15-11.49 ml sphere.It was obviously lower in the limbic of sphere than that in the center of sphere.And the quantitative errors were decreased along with the decreased of VOI size (r=0.999,0.992,0.994 and 0.767,P＜0.05).However,the quantitative error was no obviously correlation with the VOI size (r=0.348,0.478,P＞0.05) in the 26.52 ml and 0.52 ml sphere.The average quantitative error was lower in high TBR imaging (44.19％) than that in low TBR imaging (-46.18％),and it was lower in 20 s/frame imaging (-44.33％) than that in 10 s/frame imaging (-46.04％).Conclusion The quantitative accurate could be obviously affected by the partial volume effect in SPECT/CT imaging,exceptionally in the small lesions and the limbic of lesions.

Diagnosing Small Hepatic Cysts on Multidetector CT: an Additional Merit of Thinner Coronal Reformations

OBJECTIVE: We wanted to validate the additional merit of the thinner coronal reformation images from multidetector CT (MDCT) for making the diagnosis of hepatic cysts. MATERIALS AND METHODS: For the 90 benign hepatic cysts confirmed on MRI, the transverse (5-mm thickness) and additional coronal (2-mm thickness) reformation images from MDCT were compared with each other in terms of the Hounsfield units (HUs) and the size of each hepatic cyst. RESULTS: The attenuations (mean: 17.2 HUs, standard deviation: +/- 14.4) on the thinner coronal images were significantly lower than those (mean: 40.7 HUs; standard deviation: +/- 20.6) on the thicker transverse images for the small hepatic cysts (< or = 10 mm on the transverse image, p < 0.01). Twenty-three (79%) of the 29 cysts between 5 mm and 10 mm and 21 (51%) of 41 lesions up to 5 mm showed a mean HU value of 20 or less on the coronal reformation images. CONCLUSION: By reducing the partial volume effect, routine coronal reformation of MDCT with a thinner section thickness can provide another merit for making a confidential diagnosis of many small sub-centimeter hepatic cysts, and these small cysts are not easily characterized on the conventional transverse images.

Correção do efeito de volume parcial em medicina nuclear: avaliação com Phantom matemático / Partial volume effect correction in nuclear medicine: assessment with a mathematical phantom

OBJETIVO: Avaliação da correção do efeito de volume parcial pelo método iterativo de Van Cittertem medicina nuclear, usando um phantom matemático. MATERIAL E MÉTODO: Foi simulada uma imagem de quatro fontes circulares de diferentes diâmetros com intensidade igual a 255 por pixel.O algoritmo iterativo de Van Cittert foi aplicado com 20 iterações e α = 1. Foram obtidas as contagensmáximas e médias na imagem inteira e em regiões de interesse colocadas sobre cada uma das fontes. Também foram extraídos os perfis de contagem traçados ao longo do diâmetro de cada uma das fontes. RESULTADOS: A convergência local depende do tamanho da fonte estudada: quanto menor a fonte, maior o número de iterações necessário. Também depende da informação extraída: a contagem média fornece informações mais homogêneas que a contagem máxima. Há melhora significativa do contraste da imagem. CONCLUSÃO: Este estudo mostrou a possibilidade de melhora quantitativa e qualitativa ao aplicar o método bidimensional de Van Cittert em imagens de geometria simples.

OBJECTIVE: Assessment of Van Cittert partial volume effect correctionmethod in nuclear medicine images, with a mathematical phantom. MATERIAL AND METHOD: We simulated an image of four circular sources of different diameters and intensity of 255 per pixel. The iterative algorithm was applied with 20 iterations and α = 1. We obtained the maximum and average counts on the entire image and in regions of interest placed on each of the sources. We also extracted count profiles plotted along the diameter of each of the sources. RESULTS: The local convergence depends on the size of the source studied: the smaller the source, the greater the number of iterations required. It also depends on the information extracted: the use of average counts provides more homogeneous results than the maximum count. There is a significant improvement in imagecontrast. CONCLUSION: This study showed the possibility of qualitativeand quantitative improvement in applying the bidimensionaliterative Van Cittert method to images of simple geometry.

A Refined Method for Quantification of Myocardial Blood Flow using N-13 Ammonia and Dynamic PET / 대한핵의학회잡지

Regional myocardial blood flow (rMBF) can be noninvasively quantified using N-13 ammonia and dynamic positron emission tomography (PET). The quantitative accuracy of the rMBF values, however, is affected by the distortion of myocardial PET images caused by finite PET image resolution and cardiac motion. Although different methods have been developed to correct the distortion typically classified as partial volume effect and spillover, the methods are too complex to employ in a routine clinical environment. We have developed a refined method incorporating a geometric model of the volume representation of a region-of-interest (ROI) into the two- compartment N-13 ammonia model. In the refined model, partial volume effect and spillover are conveniently corrected by an additional parameter in the mathematical model. To examine the accuracy of this approach, studies were performed in 9 coronary artery disease patients. Dynamic transaxial images (16 frames) were acquired with a GE AdvanceTM PET scanner simultaneous with intravenous injection of 20 mCi N-13 ammonia. rMBF was examined at rest and during pharmacologically (dipyridamole) induced coronary hyperemia. Three sectorial myocardium (septum, anterior wall and lateral wall) and blood pool time-activity curves were generated using dynamic images from manually drawn ROIs. The accuracy of rMBF values estimated by the refined method was examined by comparing to the values estimated using the conventional two-compartment model without partial volume effect correction. rMBF values obtained by the refined method linearly correlated with rMBF values obtained by the conventional method (108 myocardial segments, correlation coefficient (r)=0.88). Additionally, underestimated rMBF values by the conventional method due to partial volume effect were corrected by theoretically predicted amount in the refined method (slope(m)=1.57). Spillover fraction estimated by the two methods agreed well (r=1.00, m=0.98). In conclusion, accurate rMBF values can be efficiently quantified by t.