A Tissue Mimicking Polyacrylamide Hydrogel Phantom for Visualizing Thermal Lesions Generated by High Intensity Focused Ultrasound

An optically transparent tissue-mimicking (TM) phantom whose acoustic properties are close to those of tissue was constructed for visualizing therapeutic effects by high intensity focused ultrasound (HIFU). The TM phantom was designed to improve a widely used standard bovine serum albumin (BSA) polyacrylamide hydrogel (PAG), which attenuated ultrasound far less than tissue and, unlike tissue, did not scatter ultrasound. A modified recipe has been proposed in the study by adding scattering glass beads with diameters of 40–80 μm (0.002% w/v) and by raising the concentration of acrylamide (30% v/v). The TM BSA-PAG constructed has an acoustic impedance of 1.67 MRayls, a speed of sound of 1576 m/s, an attenuation coefficient of 0.52 dB/cm at 1 MHz, a backscattering coefficient of 0.242 × 10⁻³ 1/sr/cm at 1 MHz and a nonlinear parameter (B/A) of 5.7. These parameters are close to those of liver. The thermal and optical properties are almost the same as the standard BSA-PAG. The characteristic features of the thermal lesions by HIFU were observed to be more accurately visualized in the TM BSA-PAG than in the standard BSA-PAG. In conclusion, the proposed TM BSA-PAG acoustically mimics tissue better than the standard BSA-PAG and is expected to be preferentially used for assuring if a clinical HIFU device produces the thermal lesion as planned.     

Motor and parietal cortex stimulation for phantom limb pain and sensations

Limb amputation may lead to chronic painful sensations referred to the absent limb, ie phantom limb pain (PLP), which is likely subtended by maladaptive plasticity. The present study investigated whether transcranial direct current stimulation (tDCS), a noninvasive technique of brain stimulation that can modulate neuroplasticity, can reduce PLP. In 2 double-blind, sham-controlled experiments in subjects with unilateral lower or upper limb amputation, we measured the effects of a single session of tDCS (2 mA, 15 min) of the primary motor cortex (M1) and of the posterior parietal cortex (PPC) on PLP, stump pain, nonpainful phantom limb sensations and telescoping. Anodal tDCS of M1 induced a selective short-lasting decrease of PLP, whereas cathodal tDCS of PPC induced a selective short-lasting decrease of nonpainful phantom sensations; stump pain and telescoping were not affected by parietal or by motor tDCS. These findings demonstrate that painful and nonpainful phantom limb sensations are dissociable phenomena. PLP is associated primarily with cortical excitability shifts in the sensorimotor network; increasing excitability in this system by anodal tDCS has an antalgic effect on PLP. Conversely, nonpainful phantom sensations are associated to a hyperexcitation of PPC that can be normalized by cathodal tDCS. This evidence highlights the relationship between the level of excitability of different cortical areas, which underpins maladaptive plasticity following limb amputation and the phenomenology of phantom limb, and it opens up new opportunities for the use of tDCS in the treatment of PLP.     

磁共振综合测试体模的设计

目的设计并测试自制MR综合测试体模。方法按照国家卫生行业标准,采用机械加工聚甲基丙烯酸甲酯组件并组合装配,制作MR体模。体模具有三向定位、满周星(楔)形测试调制传递函数(MTF)、正交双测试等独有设计,并与美国Magphan SMR170柱形综合测试体模进行实验比较。结果对自制体模与美国Magphan体模分别在场强0.36T(1个)和1.5T(2个)的临床医学MR系统上进行综合检测试验。自制体模能正常测试12项测试参数(空间定位、弛豫值、高对比度分辨率、低对比度分辨率、几何畸变、线性度、均匀度、SNR、流体测试、层厚、层偏差、MTF),结果均准确,其中低对比度分辨率、MTF、弛豫值优于美国Magphan体模。结论自制MR综合测试体模性能良好,可有效替代国外同类产品,成本较低,能满足常规MR质量控制与保障工作。     

Impact of dose reduction and the use of an advanced model-based iterative reconstruction algorithm on spectral performance of a dual-source CT system: A task-based image quality assessment

PurposeTo assess the impact of dose reduction and the use of an advanced modeled iterative reconstruction algorithm (ADMIRE) on image quality in low-energy monochromatic images from a dual-source dual energy computed tomography CT (DSCT) platform.Materials and methodsAcquisitions on an image-quality phantom were performed using DSCT equipment with 100/Sn150 kVp for four dose levels (CTDI_vol: 20/11/8/5mGy). Raw data were reconstructed for six energy levels (40/50/60/70/80/100 keV) using filtered back projection and two levels of ADMIRE (A3/A5). Noise power spectrum (NPS) and task-based transfer function (TTF) were calculated on virtual monoenergetic images (VMIs). Detectability index (d′) was computed to model the detection task of two enhanced iodine lesions as function of keV.ResultsNoise-magnitude was significantly reduced between 40 to 70 keV by ?56 ± 0% (SD) (range: ?56%–?55%) with FBP; ?56 ± 0% (SD) (?56%–?56%) with A3; and ?57 ± 1% (SD) (range: ?57%–?56%) with A5. The average spatial frequency of the NPS peaked at 70 keV and decreased as ADMIRE level increased. TTF values at 50% were greatest at 40 keV and shifted towards lower frequencies as the keV increased. The detectability of both lesions increased with increasing dose level and ADMIRE level. For the simulated lesion with iodine at 2 mg/mL, d’ values peaked at 70 keV for all reconstruction types, except for A3 at 20 mGy and A5 at 11 and 20 mGy, where d’ peaked at 60 keV. For the other simulated lesion, d’ values were highest at 40 keV and decreased beyond.ConclusionAt low keV on VMIs, this study confirms that iterative reconstruction reduces the noise magnitude, improves the spatial resolution and increases the detectability of enhanced iodine lesions.     

Neuroimaging the pain network – Implications for treatment

In this chapter, we provide an overview of neuroimaging studies in chronic pain. We start with an introduction about the phenomenology of pain. In the following section, the application of functional and structural imaging techniques is shown in selected chronic pain syndromes (chronic back pain, fibromyalgia syndrome (FMS), phantom limb pain, and complex regional pain syndrome (CRPS)), and commonalities and peculiarities of imaging correlates across different types of chronic pain are discussed. We conclude this chapter with implications for treatments, with focus on behavioral interventions, sensory and motor trainings, and mirror and motor imagery trainings.     

Low-Echo Sphere Phantoms and Methods for Assessing Imaging Performance of Medical Ultrasound Scanners

Tissue-mimicking phantoms and software for quantifying the ability of human observers to detect small low-echo spheres as a function of depth have been developed. Detectability is related to the imager's ability to delineate the boundary of a 3-D object such as a spiculated tumor. The phantoms accommodate a broad range of transducer shapes and sizes. Three phantoms are described: one with 2-mm-diameter spheres (for higher frequencies), one with 3.2-mm-diameter spheres (for lower frequencies) and one with 4-mm-diameter spheres (for lower frequencies). The spheres are randomly distributed in each phantom. The attenuation coefficients of spheres and surroundings are nearly identical; thus, compromising shadowing or enhancement distal to spheres does not occur. Reproducibility results are given for pairs of independent data sets involving eight different combinations of scanner, transducer and console settings. The following comparison results are also reported: (i) only the selected frequency differs; (ii) transducers and scan parameters are nearly the same but manufacturers differ; (iii) ordinary B-scanning, spatial compounding and tissue harmonic imaging are addressed. The phantoms and software promise to be valuable tools for scanning system and setup comparisons and for acceptance testing.     

HW-Plan放射治疗计划系统的实验验证

本文采用辐射胶片结合指形电离室的测量方法,借鉴AAPM 51号报告的电离室测量方法和AAMP 55报告中对放射治疗计划系统验证的推荐标准,对本实验室新研发的HW-Plan放射治疗计划系统进行了实验验证,内容包括点剂量、轴向剂量分布曲线以及等剂量曲线的验证比较.实验采用方形水模和有机玻璃模体,通过CT扫描确定模体的电子密度和模拟靶点(测量位置),采用PTW电离室测量在三野交叉共面、等中心照射条件下等中心点和偏等中心点的照射剂量,采用Kodak EDR2辐射胶片测量该条件下靶区剂量场的相对分布,并与计划系统在相同照射条件下计算的剂量场进行了验证比较,实现了对HW-Plan放射治疗计划系统验证,为计划系统的市场准入和进入临床应用提供了可靠的依据.     

血管位置及血管与声轴角度对HIFU表面消融效果影响的体模实验

目的探讨靶区内血管位置及血管与声轴角度对HIFU表面消融效果的影响。方法将56块含血管的仿组织体模分为A组(血管位置)和B组(血管角度),A组按血管中心与HIFU表面消融最深层面(顶面)距离d分为A_1(d=0)、A_2(d=10mm)、A_3(d=20mm)亚组,B组按血管长轴与声轴之间夹角角度α分为B_1(0~5°)、B_2(60°~65°)、B_3(90°~95°)、B_4(115°~120°)亚组。另设A_4、B_5亚组为空白对照组。测量各组血管内径、管壁厚度,观察辐照后损伤形态,计算能效因子(EEF)。结果 A、B各亚组间血管内径、管壁厚度差异均无统计学意义(P均0.05)。损伤形态:A_1、B_1亚组靶区完全消融,无残留;余各亚组血管深侧靶区有残留。A组中A_4亚组、A_1亚组、A_2亚组(由小到大排列)EEF两两比较差异均有统计学意义(P均0.05),A_1与A_3亚组差异无统计学意义(P0.05);B组中B_5亚组、B_2亚组、B3亚组(由小到大排列)EEF两两比较差异均有统计学意义(P均0.05),B_2亚组与B_4亚组、B_5亚组与B_1亚组的EEF差异无统计学意义(P均0.05)。结论血管中心距HIFU表面消融最深层面10mm、靶区内血管与声轴角度90°~95°对靶区消融影响最大,效率最低,消融时应注意调整以提高消融效率。     

脊髓损伤后的肢体幻像现象

目的对脊髓损伤后的肢体幻像现象进行临床分析,并对其发生机理进行探讨。方法通过对２８例脊髓损伤患者６～３６个月的随访,对脊髓损伤后肢体幻像的类型、性质、出现和消失时间、伤后意识障碍的有无与肢体幻像的关系等进行了分析研究。结果根据患者对麻痹肢体感觉的不同,肢体幻像可分为位置幻像和截肢幻觉两种类型。大部分肢体幻像发生于损伤初期,多在伤后半年内消失。肢体幻像的发生与伤后意识障碍之间没有明显的相关性。结论脊髓损伤后肢体幻像现象的发生可能是由于末梢神经向中枢神经传导中断而引发的异常神经活动所致。肢体幻像是一种可以随着视觉信息的不断输入而得到修正,可以自行消失的现象。     

A novel phantom design for emission tomography enabling scatter- and attenuation-”free” single-photon emission tomography imaging

A newly designed technique for experimental single-photon emission tomography (SPET) and positron emission tomography (PET) data acquisition with minor disturbing effects from scatter and attenuation has been developed. In principle, the method is based on discrete sampling of the radioactivity distribution in 3D objects by means of equidistant 2D planes. The starting point is a set of digitised 2D sections representing the radioactivity distribution of the 3D object. Having a radioactivity-related grey scale, the 2D images are printed on paper sheets using radioactive ink. The radioactive sheets can be shaped to the outline of the object and stacked into a 3D structure with air or some arbitrary dense material in between. For this work, equidistantly spaced transverse images of a uniform cylindrical phantom and of the digitised Hoffman rCBF phantom were selected and printed out on paper sheets. The uniform radioactivity sheets were imaged on the surface of a low-energy ultra-high-resolution collimator (4 mm full-width at half-maximum) of a three-headed SPET camera. The reproducibility was 0.7% and the uniformity was 1.2%. Each rCBF sheet, containing between 8.3 and 80 MBq of ^99mTcO₄ ^– depending on size, was first imaged on the collimator and then stacked into a 3D structure with constant 12 mm air spacing between the slices. SPET was performed with the sheets perpendicular to the central axis of the camera. The total weight of the stacked rCBF phantom in air was 63 g, giving a scatter contribution comparable to that of a point source in air. The overall attenuation losses were <20%. A second SPET study was performed with 12-mm polystyrene plates in between the radioactive sheets. With polystyrene plates, the total phantom weight was 2300 g, giving a scatter and attenuation magnitude similar to that of a patient study. With the proposed technique, it is possible to obtain ”ideal” experimental images (essentially built up by primary photons) for comparison with ”real” images degraded by photon scattering and attenuation losses. The method can serve as a tool for experimental validation and intercomparison of attenuation and scatter correction methods. Moreover, the large flexibility of this phantom design will allow investigations of arbitrary activity distributions and autoradiography or other imaging techniques such as PET, x-ray computed tomography or magnetic resonance imaging. Received 8 August and in revised form 21 September 1999