Improved fat–water reconstruction algorithm with graphics hardware acceleration

Purpose:

To develop a fast and robust Iterative Decomposition of water and fat with Echo Asymmetry and Least‐squares (IDEAL) reconstruction algorithm using graphics processor unit (GPU) computation.

Materials and Methods:

The fat–water reconstruction was expedited by vectorizing the fat–water parameter estimation, which was implemented on a graphics card to evaluate potential speed increases due to data‐parallelization. In addition, we vectorized and compared Brent's method with golden section search for the optimization of the unknown field inhomogeneity parameter (ψ) in the IDEAL equations. The algorithm was made more robust to fat–water ambiguities using a modified planar extrapolation (MPE) of ψ algorithm. As compared to simple planar extrapolation (PE), the use of an averaging filter in MPE made the reconstruction more robust to neighborhoods poorly fit by a two‐dimensional plane.

Results:

Fat–water reconstruction time was reduced by up to a factor of 11.6 on a GPU as compared to CPU‐only reconstruction. The MPE algorithms incorrectly assigned fewer pixels than PE using careful manual correction as a gold standard (0.7% versus 4.5%; P < 10^?4). Brent's method used fewer iterations than golden section search in the vast majority of pixels (6.8 ± 1.5 versus 9.6 ± 1.6 iterations).

Conclusion:

Data sets acquired on a high field scanner can be quickly and robustly reconstructed using our algorithm. A GPU implementation results in significant time savings, which will become increasingly important with the trend toward high resolution mouse and human imaging. J. Magn. Reson. Imaging 2010; 31: 457–465. © 2010 Wiley‐Liss, Inc.

     

Bone mineral density in cone beam computed tomography: Only a few shades of gray

Cone beam computed tomography (CBCT) has often been used to determine the quality of craniofacial bone structures through the determination of mineral density, which is based on gray scales of the images obtained. However, there is no consensus regarding the accuracy of the determination of the gray scales in these exams. This study aims to provide a literature review concerning the reliability of CBCT to determine bone mineral density. The gray values obtained with CBCT show a linear relationship with the attenuation coefficients of the materials, Hounsfield Units values obtained with medical computed tomography, and density values from dual energy X-ray absorciometry. However, errors are expected when CBCT images are used to define the quality of the scanned structures because these images show inconsistencies and arbitrariness in the gray values, particularly when related to abrupt change in the density of the object, X-ray beam hardening effect, scattered radiation, projection data discontinuity-related effect, differences between CBCT devices, changes in the volume of the field of view (FOV), and changes in the relationships of size and position between the FOV and the object evaluated. A few methods of mathematical correction of the gray scales in CBCT have been proposed; however, they do not generate consistent values that are independent of the devices and their configurations or of the scanned objects. Thus, CBCT should not be considered the examination of choice for the determination of bone and soft tissue mineral density at the current stage, particularly when values obtained are to be compared to predetermined standard values. Comparisons between symmetrically positioned structures inside the FOV and in relation to the exomass of the object, as it occurs with the right and left sides of the skull, seem to be viable because the effects on the gray scale in the regions of interest are the same.     

Assessment of the bone mineral density in the lumbar vertebrae of newborns by quantitative computed tomography

 Objective. To assess the true mineral density (BMD, in g/cm³) of the lumbar spine in newborns. Design and patients. A post-mortem analysis of five infants with gestational ages ranging from 35 to 40 weeks, and birth weights from 2765 to 3200 g, was conducted using dual-energy quantitative computed tomography (QCT; Siemens Somatom DR). A 2 or 4 mm thick slice was obtained for each lumbar vertebra from L1 to L4. The density measured in these vertebrae was corrected by reference to a solid phantom (Osteo-CT) measured simultaneously. A three-dimensional image of the spine (Elscint CT Twin), as well as a photomicrograph of histological preparation from L2 vertebra, were also obtained in another term baby for comparison with the CT results. Results and conclusions. In the range of values studied, the vertebral densities were not dependent on birth weight. BMD values measured in L2, L3 and L4 were not significantly different, but were 10% lower than in L1 in four of five infants. The spatial resolution of the QCT protocol used (0.4 mm) did not permit the differentiation of trabecular and cortical bone, and the vertebral bodies appeared very homogeneous and dense, with a mean density value of 210±30 mg Ca/cm³, which is 2.5 times higher than the mean maximum value found in young normal adults. These preliminary results highlight the potential of QCT in neonatology. Special protocols will, however, need to be developed for in vivo measurements in this particular paediatric field.     

Accuracy of single-energy quantitative computed tomography in the assessment of bone mineral density of cervical vertebrae

Earlier studies have shown that single-energy quantitative computed tomography (SEQCT) is a reliable method for bone mineral density (BMD) measurements in thoracic and lumbar vertebrae. Moreover, SEQCT has proved to be a useful parameter in the selection of appropriate implants in cervical spondylodesis. The aim of this study was to determine the accuracy of SEQCT in cervical vertebrae BMD measurement. BMD with reference to calcium hydroxyapatite (Ca₁₀[PO₄]₆[OH]₂) was assessed by SEQCT in 100 human vertebral bodies of the cervical spine. Bone cylinders were then cut from the appropriate region of interest. The cylinder volume was determined by the liquid displacement technique. The density of the mineral component was measured following incineration at 1100 °C for 24 h. The calculated BMD was correlated with the SEQCT values, resulting in a coefficient of r = 0.79 (P < 0.01). Mean SEQCT values were significantly lower than those determined by direct density assessment (t-test for coupled sampling, P < 0.02). This result was in agreement with studies on thoracic and lumbar vertebrae. These data suggest that SEQCT can reliably measure BMD in the cervical spine. Received 12 July 1996; Revision received 17 January 1997; Accepted 10 March 1997     

宝石CT能谱成像测定成人骨密度初步研究

目的 利用宝石CT能谱成像测定健康成人L3椎体骨钙含量,为能谱CT测定成人骨密度提供参考依据.方法 选取行腹部或腰椎宝石CT能谱扫描的235例患者为研究对象,其中男113例,女122例,除外有肿瘤史、外伤史、手术史及其他影响骨密度疾病的患者;年龄20～87岁,按每10岁为一年龄组,分为20～29岁、30～39岁、40～49岁、50～59岁、60～69岁、70～79岁、≥80岁组,共7个组.将扫描数据重建为层厚、间隔均为0.625 mm的Mono图像传至ADW4.4工作站,利用GSI处理器获得L3椎体水基和钙基物质图像,在椎体骨松质层面测量3个感兴趣区(ROI),取其均值.对年龄与椎体GSI钙-水密度值、水-钙密度值行Pearson相关性分析,男女各年龄组间差异行t检验.结果 男性20～29岁组椎体GSI钙-水密度值、水-钙密度值最高,女性30～39岁组椎体GSI钙-水密度值、水-钙密度值最高,男性和女性年龄与椎体GSI钙-水密度值、水-钙密度值均呈负相关(r=-0.681 5,r=-0.887 7;r=-0,796 1,r=-0.9065;P均＜0.01),女性≤39岁者随年龄增长椎体GSI钙水密度值、水-钙密度值呈轻度增高现象,但女性≤39岁者年龄与椎体GSI钙-水密度值、水-钙密度值间无明显相关性(r=0.190 1,P=0.373 5;r=-0.023 3,P=0.914 0),女性≥40岁者年龄与椎体GSI钙-水密度值、水-钙密度值呈负相关(r=-0.793 9,r=-0.867 5,P均＜0.01).男性和女性自50岁开始GSI钙-水密度值组间差异具有统计学意义(P均＜0.01).结论 宝石CT能谱成像是测量椎体骨密度的新方法,可用来测量椎体骨密度.     

Improved pelvicalyceal visualization with multidetector computed tomography urography; comparison with helical computed tomography

Our aim was to compare the quality of pelvicalyceal visualization on computed tomography (CT) urography using a small intravenous contrast material dose, hydration, and high-resolution multidetector CT (MDCT) with that of conventional helical CT. The test (MDCT) group (49 consecutive patients, 98 kidneys) was scanned 5 min following an intravenous bolus of 30 ml of iodinated contrast material. The control (helical CT) group (50 consecutive patients, 95 kidneys) was scanned 5 min following injection of 120–150 ml of intravenous contrast material. Enhancement and quality of calyceal detail were measured using a five-scale grading system (1 for no detail, 5 for cupped calyces). Calyceal attenuation was substantial in both groups (more than 220 Hounsfield units, HU) but less in the test group compared with the control group (mean 475 and 920 HU, respectively), p<0.0001. In the test group, the calyceal attenuation was less than 500 HU in the majority of cases (65/98 kidneys), while the opposite was true for the control group, where calyceal attenuation was more than 750 HU in 50/95 kidneys (p<0.001). The quality of calyceal detail was 3.4/5 in the test group compared with 1.8/5 in the control group (p<0.0001). The combination of hydration, low-contrast dose, and the high image resolution achieved with MDCT significantly improves calyceal visualization in CT urography.     

Spinal bone mineral density by quantitative CT in a normal Italian population

The purpose of this study was to describe the normal cross-sectional pattern of spinal bone loss associated with aging in an Italian population and to compare these values to the American normative database. A group of 472 healthy subjects (382 females and 90 males) were recruited for bone mineral density (BMD) assessment by quantitative computed tomography (QCT). To eliminate technique-related differences in a comparison of Italian and American normal values obtained with two different scanners we performed a cross-calibration analysis scanning the same computerized imaging reference system (CIRS) phantom at both centers. The results of the cross-calibration study using the CIRS phantom were used to compare regression slopes of BMD with age and age-adjusted mean BMD of American men and women vs cross-calibrated Italian men and women. American men and women decrease more rapidly vs Italian men and women, and Italian men have significantly lower age-adjusted mean BMD than American men. For these reasons we recommend normal values to be locally obtained for an Italian population. Correspondence to: G. Guglielmi     

Bone mineral and other bone components in vertebrae evaluated by QCT and MRI

To evaluate the usefulness of assessing bone components using magnetic resonance imaging (MRI), the contributions of bone components, including mineral, fat and collagen, to bone mineral density (BMD) and T1 relaxation time (T1) were studied using phantoms. Excised human vertebrae were also evaluated by quantitative computed tomography (QCT) and MRI. T1 was shortened with increasing quantities of fat and collagen. In water, T1 was significantly affected by bone density, while in oil, T1 became slightly longer as bone density increased. The presence of fat and collagen caused under- and overestimations of BMD, respectively. There was good correlation between T1 and BMD in osteoporotic vertebrae and the vertebrae with long T1 showed an increased content of hematopoietic marrow and/or abnormally increased bone mineral. It was concluded that the experimental data showed that MRI can contribute to the assessment of bone quality.     

Quantitative bone matrix density measurement by water‐ and fat‐suppressed proton projection MRI (WASPI) with polymer calibration phantoms

The density of the organic matrix of bone substance is a critical parameter necessary to clinically evaluate and distinguish structural and metabolic pathological conditions such as osteomalacia in adults and rickets in growing children. Water‐ and fat‐suppressed proton projection MRI (WASPI) was developed as a noninvasive means to obtain this information. In this study, a density calibration phantom was developed to convert WASPI intensity to true bone matrix density. The phantom contained a specifically designed poly(ethylene oxide)/poly(methyl methacrylate) (PEO/PMMA) blend, whose MRI properties (T₁, T₂, and resonance linewidth) were similar to those of solid bone matrix (collagen, tightly bound water, and other immobile molecules), minimizing the need to correct for differences in T₁ and/or T₂ relaxation between the phantom and the subject. Cortical and trabecular porcine bone specimens were imaged using WASPI with the calibration phantom in the field of view (FOV) as a stable intensity reference. Gravimetric and amino acid analyses were carried out on the same specimens after WASPI, and the chemical results were found to be highly correlated (r² = 0.98 and 0.95, respectively) to the WASPI intensity. By this procedure the WASPI intensity can be used to obtain the true bone matrix mass density in g cm^–3. Magn Reson Med 60:1433–1443, 2008. © 2008 Wiley‐Liss, Inc.     

长期血液透析患者腰椎骨密度定量CT的检测及意义

目的　研究长期维持性血液透析患者骨密度的变化 ,探讨腰椎QCT -BMD检测的应用价值。方法　 5 0例长期血液透析患者按不同透析年限分组 ,应用QCT技术分别检测其 2～ 4腰椎椎体松质骨BMD ,并与年龄、性别相匹配的正常人腰椎BMD进行比较分析。结果　 5 0例血液透析患者有 45例 (90 .0 % )骨密度降低 (T值 <-1.0 ) ,其中 2 0例 (4 0 .0 % )T值 <-2 .5 ,明显低于相应年龄性别正常对照组 ,并随透析时间延长患者BMD进一步降低。结论　长期血液透析患者骨矿含量明显降低且与透析时间呈正相关 ,QCT -BMD检测敏感性和准确性高 ,对肾性骨病的早期诊断具有较大的应用价值。     

Quantitation of T2′ anisotropic effects on magnetic resonance bone mineral density measurement

In this paper, the authors quantitate the anisotropy of susceptibility effects in an uniaxial trabecular bone model and show its relevance to clinical MR bone mineral density measurements. A physical model is described that quantitates the anisotropic MR behavior of uniaxial trabecular bone. To test the model, a phantom of parallel polyethylene filaments was scanned every 15° between 0° and 90° with respect to the system's main magnetic field (B₀). The distal radial metaphysis of a healthy female volunteer was scanned in orthogonal projections. The signal from each phantom image and each radial image was separated in a pixel-wise fashion into R₂ and R₂′ maps. As predicted, R₂′ relaxation showed anisotropic behavior and changed according to sin² (?), confirming that columnar structures parallel with B₀ will cause no MR susceptibility effects. Scans of the distal radius showed that R₂′ relaxation was twice as great with the forearm perpendicular to B₀ as when it was parallel to it, demonstrating different contributions from struts and columns. For both phantom and radial bone scans, R₂ relaxation was isotropic and did not change with object orientation.     

脑瘫患儿骨密度与疾病严重程度的相关性

 目的 探讨脑瘫患儿骨密度与疾病严重程度的相关性。方法 选取在南方医科大学第三附属医院就诊随访的1~4岁脑瘫患儿142例,按体格发育情况分为脑瘫发育迟缓组(82例)和脑瘫发育正常组(60例);按粗大运动功能分类系统(GMFCS)分为运动功能轻度障碍组40例(GMFCS 1～2级)、中度障碍组72例(GMFCS 3～4级)、重度障碍组30例(GMFCS5级),同时选取正常发育儿童57例作为对照组。探讨椎体和股骨近端骨密度、血清钙水平及胰岛素样生长因子-1(IGF-1)在各组之间的差异性,以及骨密度与GMFCS 分级的相关性。结果 脑瘫患儿的椎体和股骨近端的BMD水平明显低于健康对照组[腰椎(0.46±0.11) g/cm² vs (0.56±0.13) g/cm²,P<0.001;股骨近端(0.43±0.06)g/cm² vs (0.53±0.12)g/cm²,P<0.001]。脑瘫患儿椎体和股骨近端水平BMD与GMFCS分级之间呈显著负相关性(腰椎r=-0.363,P<0.001;股骨近端r=-0.491,P<0.001)。脑瘫患儿的血清钙及IGF-1水平明显低于健康对照组,GMFCS分级越高,血清钙及IGF-1水平就越低。结论 脑瘫患儿骨密度与疾病严重程度呈负相关性,表明脑瘫患儿骨代谢水平异常。