Quantitation of in vitro coronary artery calcium using ultrafast computed tomography

Ultrafast computed tomography (UFCT) has the potential to quantify coronary hydroxyapatite (HAP). However, no definitive studies validating this technique are available. We constructed a human chest phantom model with coronary arteries represented by cylindrical holes containing: (1) calcium chloride solutions, (2) a block of HAP immersed in paraffin (without partial volume effect), and (3) HAP granules embedded in a gelatin matrix (with partial volume effect). We scanned this model to determine the relationship between measured CT number per voxel and density of the calcium per voxel. The relationships between CT number and concentration of calcium chloride was linear (r = 0.992 to 0.999). Using a commercially available standard bone mineral phantom, we were able to estimate the concentration of HAP to an accuracy from 94 to 97% when partial volume effects were absent. However, when partial volume effects were present, two methods of estimating HAP produced significant errors (1 to 384%, and 17 to 52%). We conclude that significant partial voluming errors degrade the accuracy of HAP quantitation and that further evaluation and corrections are needed before such quantitation is clinically applied. © 1994 Wiley-Liss,Inc..     

A novel MRI-compatible brain ventricle phantom for validation of segmentation and volumetry methods

Purpose:

To create a standardized, MRI‐compatible, life‐sized phantom of the brain ventricles to evaluate ventricle segmentation methods using T₁‐weighted MRI. An objective phantom is needed to test the many different segmentation programs currently used to measure ventricle volumes in patients with Alzheimer's disease.

Materials and Methods:

A ventricle model was constructed from polycarbonate using a digital mesh of the ventricles created from the 3 Tesla (T) MRI of a subject with Alzheimer's disease. The ventricle was placed in a brain mold and surrounded with material composed of 2% agar in water, 0.01% NaCl and 0.0375 mM gadopentetate dimeglumine to match the signal intensity properties of brain tissue in 3T T₁‐weighted MRI. The 3T T₁‐weighted images of the phantom were acquired and ventricle segmentation software was used to measure ventricle volume.

Results:

The images acquired of the phantom successfully replicated in vivo signal intensity differences between the ventricle and surrounding tissue in T₁‐weighted images and were robust to segmentation. The ventricle volume was quantified to 99% accuracy at 1‐mm voxel size.

Conclusion:

The phantom represents a simple, realistic and objective method to test the accuracy of lateral ventricle segmentation methods and we project it can be extended to other anatomical structures. J. Magn. Reson. Imaging 2012;36:476–482. © 2012 Wiley Periodicals, Inc.     

Development of an Anthropomorphic Shoulder Phantom Model That Simulates Bony Anatomy for Sonographic Measurement of the Acromiohumeral Distance

The purpose of this project was to create a sonographic phantom model of the shoulder that was accurate in bone configuration. Its main purpose was for operator training to measure the acromiohumeral distance. A computerized 3‐dimensional model of the superior half of the humerus and scapula was rendered and 3‐dimensionally printed. The bone model was embedded in a gelatin compound and set in a shoulder‐shaped mold. The materials used had speeds of sound that were well matched to soft tissue and epiphyseal bone. The model was specifically effective in simulating the acromiohumeral distance because of its accurate bone geometry.     

Development of Oil-in-Gelatin Phantoms for Viscoelasticity Measurement in Ultrasound Shear Wave Elastography

Because tissues consist of solid and fluid materials, their mechanical properties should be characterized in terms of both elasticity and viscosity. Although the elastic properties of tissue-mimicking phantoms have been extensively studied and well characterized in commercially available phantoms, their viscous properties have not been fully investigated. In this article, a set of 14 tissue-mimicking phantoms with different concentrations of gelatin and castor oil were fabricated and characterized in terms of acoustic and viscoelastic properties. The results indicate that adding castor oil to gelatin phantoms decreases shear modulus, but increases shear wave dispersion. For 3% gelatin phantoms containing 0%, 10%, 20% and 40% oil, the measured shear moduli are 2.01 ± 0.26, 1.68 ± 0.25, 1.10 ± 0.22 and 0.88 ± 0.17 kPa, and the Voigt-model coupled shear viscosities are 0.60 ± 0.11, 0.89 ± 0.07, 1.05 ± 0.11 and 1.06 ± 0.13 Pa·s, respectively. The results also confirm that increasing the gelatin concentration increases shear modulus. For phantoms containing 3%, 4%, 5%, 6% and 7% gelatin, the measured shear moduli are 2.01 ± 0.26, 3.10 ± 0.34, 4.18 ± 0.84, 8.05 ± 1.00 and 10.24 ± 1.80 kPa at 0% oil and 1.10 ± 0.22, 1.97 ± 0.20, 3.13 ± 0.63, 4.60 ± 0.60 and 8.43 ± 1.39 kPa at 20% oil, respectively. The phantom recipe developed in this study can be used in validating ultrasound shear wave elastography techniques for soft tissues.     

Confocal dual‐frequency enhances the damaging effect of high‐intensity focused ultrasound in tissue‐mimicking phantom

The volume of the lesions created by conventional single‐frequency high‐intensity focused ultrasound (HIFU) is small, which leads to long treatment duration in patients who are undergoing tumor ablation. In this study, the lesions induced by confocal dual‐frequency HIFU in an optically transparent tissue‐mimicking phantom were investigated and compared with the lesions created by conventional single‐frequency HIFU. The results show that using different exposure times resulted in lesions of different sizes in both dual‐frequency and single‐frequency HIFU modes at the same spatially averaged intensity level (ISAL = 4900?W?cm^?2), but the lesion dimensions made in dual‐frequency mode were significantly larger than those made in single‐frequency mode. Difference frequency acoustic fields that exist in the confocal region of dual‐frequency HIFU may be the reason for the enlargement of the lesions' dimensions. The dual‐frequency HIFU mode may represent a new technique to improve the ablation efficiency of HIFU. The total time for the ablation of a tumor can be reduced, thus requiring less therapy time and reducing possible patient complications.     

Chronic Administration of Ketamine for Analgesia

Use of the dissociative anesthetic ketamine in subanesthetic doses has demonstrated efficacy in neuropathic pain. This article reviews the scientific and clinical literature on ketamine. Mechanisms of both central and peripheral neuropathic pain are described. Studies of ketamine analgesia in postherpetic neuralgia, phantom pain, complex regional pain syndrome and cancer pain are reviewed. A range of administration methods for ketamine including neuroaxial administration are described.     

Signal processors in duplex sonography: in vitro comparison between analog and digital methods

Using a new flow-test phantom, which respects the acoustic properties of real blood as well as the proximal and distal impedances of body circulation, we assessed the performance of two duplex sonography signal processors on blood-flow measurements. With both the analog and the dynamic signal processor (Fast Fourier Transform), the correlation between duplex sonography and quantitative flow measurements was high (0.96–0.99) for different dynamic conditions (steady or pulsatile blood flow, varying heart rate, blood pressure, and hematocrit) and for different mechanical conditions (silicon tube or animal vessel). The real blood flow was overestimated by duplex sonography the over-estimation was more pronounced with the analog processor (factor 1.87–4.20) than with the digital processor (factor 1.22–1.64,P<0.05). Applied to the study of asymmetric stenoses, the digital processor was not superior to the analog processors described in the literature.     

基于电阻抗成像的均质头模型研究

目的 评估低电导率的颅骨对人脑阻抗成像的影响.方法 基于适用于头部的优化的硬件系统和反投影算法,在建立的一个圆筒形和一个半球形的包含"颅骨"的均质头模型上,对多种扰动目标进行成像研究.结果 现有系统对含均质"颇骨"的头部物理模型内电导率、位置和尺寸不同的简单扰动目标成功地进行了图像重建.结论 "颅骨"的存在对重构图像产生了显著的影响,揭示了脑电阻抗图像监护的可行性,为动物实验提供了依据.     

A high-resolution transrectal ultrasonographic system

The design of a transrectal echographical ultrasound system is described in this paper. This system produces high-quality, gray-scale images of the prostate, seminal vesicles and the bladder. A light, hand-held probe is inserted into the rectum. The probe is covered with a thin latex sheath which is filled with water to obtain excellent acoustic coupling with the wall of the rectum. The transducer, which is placed in the tip, rotates continuously, and this generates an ultrasound beam at 90° to the probe. A balanced arm can be coupled to the probe during this procedure to obtain better position stability and patient comfort. The transducer can be detached. Most of the work has been done for a 5 MHz transducer, but sometimes a 3.5 MHz transducer is used for greater penetration (≈ 9 cm).The transmitting and receiving systems contain unusual circuits. This includes a novel high-voltage pulser that generates the ultrasound pulse, and a simple but flexible variable time-gain control that adjusts the gain in echoes from different depths. A unique gray-scale phantom, that contains a mixture of lossy gel and reflecting objects, has been used routinely to check the performance of the transrectal scanner. This help is achieving excellent images of the prostate and seminal vesicles.