Linearity and contrast scale control in computed tomography

The aim of this paper is to present linearity studies and quality control charts for changes in the computed tomography (CT) number of water and contrast scales for two CT scanners over one year. Linear regression relates the attenuation coefficient to CT number. The CT number for water and the contrast scale values as obtained from the fit are: CT1 = (-0.13 +/- 1.3) Hounsfield units (HU), CT2 = (-1.8 +/- 1.6) HU and contrast scale (CS)1 = (1.80 +/- 0.03) 10(-4) cm-1 HU-1, CS2 = (1.82 +/- 0.02) 10(-4) cm-1 HU-1 for Picker International scanner models 600SE and 1200SX, respectively. Direct measurements of CT numbers are compared with fitted results, providing a necessary preliminary steps in the development of objective CT interpretation.     

Measurement of renal extraction fraction using contrast-enhanced computed tomography

Renal extraction fraction (EF) is the percentage of plasma entering the glomerulus which is filtered. Contrast agents which are freely filtered and neither secreted nor reabsorbed, may be used as markers for renal filtration, allowing EF to be calculated from computed tomography (CT) measurements of systemic vessels and renal veins. CT scans of 10 adult patients having no known renal disease were studied in this manner, giving EF values averaging 12.6% and 12.3% for the right and left kidneys, respectively, compared to the accepted value of 15%-20%. EF measurement using CT may provide noninvasive evaluation of renal function, complementing CT-derived morphologic information.     

Independent component analysis of dynamic contrast-enhanced computed tomography images

Independent component analysis (ICA) was applied on dynamic contrast-enhanced computed tomography images of cerebral tumours to extract spatial component maps of the underlying vascular structures, which correspond to different haemodynamic phases as depicted by the passage of the contrast medium. The locations of arteries, veins and tumours can be separately identified on these spatial component maps. As the contrast enhancement behaviour of the cerebral tumour differs from the normal tissues, ICA yields a tumour component map that reveals the location and extent of the tumour. Tumour outlines can be generated using the tumour component maps, with relatively simple segmentation methods.     

Image reconstruction for fan-beam differential phase contrast computed tomography

Recently, x-ray differential phase contrast computed tomography (DPC-CT) has been experimentally implemented using a conventional tube combined with gratings. Images were reconstructed using a parallel-beam reconstruction formula. However, parallel-beam reconstruction formulae are not applicable when the parallel-beam approximation fails. In this paper, we present a new image reconstruction formula for fan-beam DPC-CT. There are several novel features of the new image reconstruction formula: (i) when the scanning angular range of data acquisition is larger than pi + gamma(m) (gamma(m) is the full fan angle), the entire field of view can be exactly reconstructed; (ii) when the scanning angular range is smaller than pi + gamma(m), a local region of interest (ROI) can be exactly reconstructed; (iii) it enables an exact reconstruction for a local ROI when the projection data are truncated at some view angles; (iv) it enlarges the imaging field of view when the detector is asymmetrically placed. In this last case, the data are truncated from every view angle. Numerical simulations have been conducted to validate the new reconstruction formula.     

Comparison of contrast-enhanced ultrasonography with grey-scale ultrasonography and contrast-enhanced computed tomography in diagnosing focal fatty liver infiltrations and focal fatty sparing

PurposeFatty liver infiltrations and fatty sparing impair diagnostic performance of grey-scale ultrasonography in differentiating malignant and benign focal liver lesions.In the study, we present our experience in diagnosing focal fatty liver infiltrations and focal fatty sparing with contrast-enhanced ultrasonography (CEUS) in comparison to grey-scale ultrasonography and contrast-enhanced computed tomography (CECT).Material and MethodThe retrospective study group (n=82 patients), included 44 (53.7%) men, 38 (46.3%) women (aged 29–81 years, mean 55.8 years) with 48 focal fatty liver infiltrations and 34 focal fatty sparing. All patients underwent grey-scale ultrasonography (US), CEUS using SonoVue^® and CECT executed within the 7 days.ResultsWith US, CEUS and CECT focal fatty liver infiltrations were diagnosed in 22, 46 and 44 cases, respectively. The following values were obtained: sensitivity ? 45.8%, 95.8% and 91.7%, specificity ? 100% for all, accuracy ? 95.2%, 99.6% and 99.3%, respectively. Focal fatty sparing was diagnosed in 16, 31 and 30 cases, respectively. The following values were obtained: sensitivity ? 47.1%, 91.2% and 88.2%, specificity ? 99.8%, 100% and 100%, accuracy ? 95.6%, 99.4% and 99.3%, respectively. No statistically significant differences were found in sensitivity of diagnosing focal fatty liver infiltrations and focal fatty liver sparing between CEUS and CECT. Sensitivity of grey-scale ultrasonography was significantly lower when compared to those of CEUS and CECT (p<0.001).ConclusionCEUS is as sensitive as CECT in focal fatty infiltrations and focal fatty sparing diagnosing. However, CEUS provides more information than CECT about the vasculature and enhancement pattern of focal fatty liver infiltrations.     

Artifact reduction method in ultrasound-guided diffuse optical tomography using exogenous contrast agents

In diffuse optical tomography (DOT), a typical perturbation approach requires two sets of measurements obtained at the lesion breast (lesion or target site) and a contra-lateral location of the normal breast (reference site) for image reconstruction. For patients who have a small amount of breast tissue, the chest-wall underneath the breast tissue at both sites affects the imaging results. In this group of patients, the perturbation, which is the difference between measurements obtained at the lesion and reference sites, may include the information of background mismatch which can generate artifacts or affect the reconstructed quantitative absorption coefficient of the lesion. Also, for patients who have a single breast due to prior surgery, the contra-lateral reference is not available. To improve the DOT performance or overcome its limitation, we introduced a new method based on an exogenous contrast agent and demonstrate its performance using animal models. Co-registered ultrasound was used to guide the lesion localization. The results have shown that artifacts caused by background mismatch can be reduced significantly by using this new method.     

Phase contrast synchrotron radiation computed tomography of muscle spindles in the mouse soleus muscle

Muscle spindles are skeletal muscle sensory organs involved in the sensation of position and movement of the body. We have explored the capability of phase contrast computed tomography to visualise muscle spindles in murine skeletal muscle. In particular, we have validated the visualisation of nerve fibres through phase contrast computed tomography using light microscopy on stained histological sections. We further present the first three‐dimensional visualisation of muscle spindles in mouse soleus skeletal muscle in conjunction with the neurovascular bundle associated with it.     

A reconstruction method for equidistant fan beam differential phase contrast computed tomography

We report a reconstruction method, called a back-projection filtered (BPF) algorithm, for fan beam differential phase contrast computed tomography (DPC-CT) with equidistant geometrical configuration. This work comprises a numerical study of the algorithm and its experimental verification with a three-grating interferometer and an x-ray tube source. The numerical simulation and experimental results demonstrate that the proposed method can deal with several classes of truncated datasets. It could be of interest in future medical phase contrast imaging applications.     

超声对比剂的材料学特点及临床应用

背景：目前临床上应用的超声对比剂均是含有不同包膜材料和气体成分的微泡对比剂,微泡对比剂的出现使超声诊断技术得到了较大的发展。 目的：探讨超声对比剂的材料学研究特点,及超声对比剂在临床疾病治疗中的应用。 方法：超声对比剂是由气体微泡和外部包裹的膜物质组成,包膜材料主要分为白蛋白、大分子脂质体、多聚体和各种表面活性剂等。超声造影是通过增强背向散射信号来成像。超声对比剂研究的发展大致分为3个阶段,造影相关技术包括二次谐波、组织特异性显像、反相脉冲谐波成像、相干造影成像技术、对比脉冲序列、能量多普勒谐波成像、间歇谐波成像技术、编码谐波成像和超声造影三维成像。 结果与结论：超声对比剂形式的不同主要是通过改变微泡包膜和气体的性质和设计来实现的。微气泡能够实现超声对比剂的显影作用,还可在药物传输上发挥功能。新型的微泡超声对比剂不仅可以提供血流灌注学信息,还可以通过靶向作用于病变组织,分析病变的发生机制,使微泡对比剂的诊断更准确。随着微泡对比剂材料学研究以及制备工艺完善,使超声对比剂具有良好的生物相容性。不仅可以用于各种状态下的特异性超声造影,还可以利用空化效应携带药物或治疗基因向目标组织转移释放。微泡造影技术具有治疗、诊断和超声成像的功能,是一种安全、高效、无创的诊断和靶向传输治疗手段。     

Four-dimensional computed tomography: image formation and clinical protocol

Respiratory motion can introduce significant errors in radiotherapy. Conventional CT scans as commonly used for treatment planning can include severe motion artifacts that result from interplay effects between the advancing scan plane and object motion. To explicitly include organ/target motion in treatment planning and delivery, time-resolved CT data acquisition (4D Computed Tomography) is needed. 4DCT can be accomplished by oversampled CT data acquisition at each slice. During several CT tube rotations projection data are collected in axial cine mode for the duration of the patient's respiratory cycle (plus the time needed for a full CT gantry rotation). Multiple images are then reconstructed per slice that are evenly distributed over the acquisition time. Each of these images represents a different anatomical state during a respiratory cycle. After data acquisition at one couch position is completed, x rays are turned off and the couch advances to begin data acquisition again until full coverage of the scan length has been obtained. Concurrent to CT data acquisition the patient's abdominal surface motion is recorded in precise temporal correlation. To obtain CT volumes at different respiratory states, reconstructed images are sorted into different spatio-temporally coherent volumes based on respiratory phase as obtained from the patient's surface motion. During binning, phase tolerances are chosen to obtain complete volumetric information since images at different couch positions are reconstructed at different respiratory phases. We describe 4DCT image formation and associated experiments that characterize the properties of 4DCT. Residual motion artifacts remain due to partial projection effects. Temporal coherence within resorted 4DCT volumes is dominated by the number of reconstructed images per slice. The more images are reconstructed, the smaller phase tolerances can be for retrospective sorting. From phantom studies a precision of about 2.5 mm for quasiregular motion and typical respiratory periods could be concluded. A protocol for 4DCT scanning was evaluated and clinically implemented at the MGH. Patient data are presented to elucidate how additional patient specific parameters can impact 4DCT imaging.     

Kidney structural characteristics based on a kidney biopsy and contrast-enhanced computed tomography in healthy living kidney donors

The demands for kidney transplantations are increasing, and so is the number of live kidney donors (LKDs). Recent studies show that LKDs have an increased risk of developing end-stage renal disease compared with healthy non-donors. However, the knowledge about factors predicting renal disease in kidney donors is sparse. Some evidence points to increased glomerular sclerosis and kidney fibrosis, as well as a low number of glomeruli as associated with a worse renal outcome. This methodological study investigated that which estimates are obtainable with a standard kidney biopsy taken from the donated kidney during the transplantation, and a standard contrast-enhanced computed tomography (CT) in kidney donors. CT-scans were used to obtain total volume of the kidney and kidney cortex using the Cavalieri estimator and 2D-nucleator. Glomerular number density in the biopsies was estimated by a model-based method, and was multiplied by total cortex volume in order to estimate the total number of glomeruli in the kidney. Glomerular volume was estimated by the 2D-nucleator and a model-based stereological technique. Kidney fibrosis (point-counting), glomerular sclerosis (evaluation of glomerular profiles), and arteriole dimensions (2D-nucleator) were also estimated in the biopsy sections from the donated kidney. Various studies have attempted to identify predictors of renal outcome in LKDs. There is no consensus yet, and further studies are needed to elucidate if and how the estimates described in this study are associated with renal outcome in LKDs.     

Transmission and dose perturbations with high-Z materials in clinical electron beams

High density and atomic number (Z) materials used in various prostheses, eye shielding, and beam modifiers produce dose enhancements on the backscatter side in electron beams and is well documented. However, on the transmission side the dose perturbation is given very little clinical importance, which is investigated in this study. A simple and accurate method for dose perturbation at metallic interfaces with soft tissues and transmission through these materials is required for all clinical electron beams. Measurements were taken with thin-window parallel plate ion chambers for various high-Z materials (Al, Ti, Cu, and Pb) on a Varian and a Siemens accelerator in the energy range of 5-20 MeV. The dose enhancement on both sides of the metallic sheet is due to increased electron fluence that is dependent on the beam energy and Z. On the transmission side, the magnitude of dose enhancement depends on the thickness of the high-Z material. With increasing thickness, dose perturbation reduces to the electron transmission. The thickness of material to reduce 100% (range of dose perturbation), 50% and 10% transmission is linear with the beam energy. The slope (mm/MeV) of the transmission curve varies exponentially with Z. A nonlinear regression expression (t=E[alpha+beta exp(-0.1Z)]) is derived to calculate the thickness at a given transmission, namely 100%, 50%, and 10% for electron energy, E, which is simple, accurate and well suited for a quick estimation in clinical use. Caution should be given to clinicians for the selection of thickness of high-Z materials when used to shield critical structures as small thickness increases dose significantly at interfaces.     

Optical tracking of contrast medium bolus to optimize bolus shape and timing in dynamic computed tomography

One of the biggest challenges in dynamic contrast-enhanced CT is the optimal synchronization of scan start and duration with contrast medium administration in order to optimize image contrast and to reduce the amount of contrast medium. We present a new optically based approach, which was developed to investigate and optimize bolus timing and shape. The time-concentration curve of an intravenously injected test bolus of a dye is measured in peripheral vessels with an optical sensor prior to the diagnostic CT scan. The curves can be used to assess bolus shapes as a function of injection protocols and to determine contrast medium arrival times. Preliminary results for phantom and animal experiments showed the expected linear behavior between dye concentration and absorption. The kinetics of the dye was compared to iodinated contrast medium and was found to be in good agreement. The contrast enhancement curves were reliably detected in three mice with individual bolus shapes and delay times of 2.1, 3.5 and 6.1 s, respectively. The optical sensor appears to be a promising approach to optimize injection protocols and contrast enhancement timing and is applicable to all modalities without implying any additional radiation dose. Clinical tests are still necessary.