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     

Effects of MR Parameter Changes on the Quantification of Diffusion Anisotropy and Apparent Diffusion Coefficient in Diffusion Tensor Imaging: Evaluation Using a Diffusional Anisotropic Phantom

Objective

To validate the usefulness of a diffusional anisotropic capillary array phantom and to investigate the effects of diffusion tensor imaging (DTI) parameter changes on diffusion fractional anisotropy (FA) and apparent diffusion coefficient (ADC) using the phantom.

Materials and Methods

Diffusion tensor imaging of a capillary array phantom was performed with imaging parameter changes, including voxel size, number of sensitivity encoding (SENSE) factor, echo time (TE), number of signal acquisitions, b-value, and number of diffusion gradient directions (NDGD), one-at-a-time in a stepwise-incremental fashion. We repeated the entire series of DTI scans thrice. The coefficients of variation (CoV) were evaluated for FA and ADC, and the correlation between each MR imaging parameter and the corresponding FA and ADC was evaluated using Spearman''s correlation analysis.

Results

The capillary array phantom CoVs of FA and ADC were 7.1% and 2.4%, respectively. There were significant correlations between FA and SENSE factor, TE, b-value, and NDGD, as well as significant correlations between ADC and SENSE factor, TE, and b-value.

Conclusion

A capillary array phantom enables repeated measurements of FA and ADC. Both FA and ADC can vary when certain parameters are changed during diffusion experiments. We suggest that the capillary array phantom can be used for quality control in longitudinal or multicenter clinical studies.     

Practical problems in neutron dosimetry

The first problem discussed is the best phantom material. It is argued that tissue composition has a greater effect on dose distributions from photons than on those from neutrons. As water is normally used for photons, it should be satisfactory for neutrons, but checks are needed with high-energy neutron beams. Another serious problem is that of kerma ratios for neutrons above 20 MeV where highly discordant values have been calculated by several authors. Finally some suggestions are made about measurement of the gamma-ray component in beams of high-energy neutrons.     

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.     

A prospective study on the neurological complications of breast cancer and its treatment: Updated analysis three years after cancer diagnosis

ObjectivesTo quantify the prevalence of neurological complications among breast cancer patients at one and three years after diagnosis, and to identify factors associated with neuropathic pain (NP) and chemotherapy-induced peripheral neuropathy (CIPN).Material and methodsProspective cohort study including 475 patients with newly diagnosed breast cancer, recruited among those proposed for surgical treatment (Portuguese Institute of Oncology, Porto). Patients underwent a neurological evaluation and had their cognitive function assesses with the Montreal Cognitive Assessment, before treatment and at one and three years after enrollment. We estimated the prevalence of each neurological complication, and odds ratios (OR), adjusted for socio-demographic and clinical characteristics, to identify factors associated with NP and CIPN.ResultsMore than half of the patients [54.7%, 95% confidence interval (95%CI): 50.2–59.2] presented at least one neurological complication, at one or at three years after cancer diagnosis. Between the first and the third year of follow-up, there was an increase in the prevalence of NP (from 21.1% to 23.6%), cognitive impairment (from 7.2% to 8.2%), cerebrovascular disease (from 0.6% to 1.5%) and brain metastasis (from 0.0% to 0.6%). The prevalence of CIPN decreased from 14.1% to 12.6%. Axillary lymph node dissection was associated with NP at one year (OR = 2.75, 95%CI: 1.34–5.63) and chemotherapy with NP at three years (OR = 2.10, 95%CI: 1.20–3.67). Taxane-based chemotherapy was strongly associated with prevalence of CIPN at one and three years.ConclusionNeurological complications are frequent even three years after cancer diagnosis and NP remained the major contributor to the burden of these conditions among survivors.     

Preoperative localization of intracranial lesions with MRI using marking pills

Objective

To describe a simple technique for preoperative surface localization of intracranial lesions.

Methods

11 pills in total, including Alfarol (alfacalcidol) capsules, were affixed to a phantom with adhesive tape and a MRI scan was performed. The visibility of the pills and any spatial errors in determining their locations were evaluated. Between June 2006 and April 2009, we employed Alfarol capsules as a skin marker in MRI in clinical surgical cases.

Results

Alfarol capsules, whose actual size is 5.6 mm in diameter, were identified as a hyperintense spot at a size of 4.2, 4.2, and 4.5 mm in diameter in T1-weighted, T2-weighted, and FLAIR (fluid attenuated inversion recovery) sequence images, respectively. The size discrepancies were within 1.4 mm. The average spatial errors were 0.7, 0.6, and 0.7 mm in T1-weighted, T2-weighted, and FLAIR sequence images, respectively. Other pills were not identified in the MRI scans.During this 35-month period, 8 patients underwent preoperative MRI-guided localization at our institution. There were 5 men and 3 women in whom 8 biopsies were performed. In all cases, the result of the biopsy was positive and useful for the treatment that followed. No perioperative complications were encountered.

Conclusion

Alfarol capsule can be used as an external skin marker. Our simple and inexpensive method is a useful addition to preoperative evaluation of superficial intracranial lesions.     

High incidence of ‘synaesthesia for pain’ in amputees

Synaesthesia for pain is a phenomenon where a person experiences pain when observing or imagining another in pain. Anecdotal reports of this type of experience have most commonly occurred in individuals who have lost a limb. Distinct from phantom pain, synaesthesia for pain is triggered specifically in response to pain in another. Here, we provide the first preliminary investigation into synaesthesia for pain in amputees to determine the incidence and characteristics of this intriguing phenomenon. Self-referring amputees (n = 74) answered questions on synaesthesia for pain within a broader survey of phantom pain. Of the participants, 16.2% reported that observing or imagining pain in another person triggers their phantom pain. Further understanding of synaesthesia for pain may provide a greater insight to abnormal empathic function in clinical populations as well as therapeutic intervention for at risk groups.     

幻肢痛的研究进展

随着交通事故、恶性疾病、自然灾害的不断增多,行截肢术的患者也越来越多.有资料显示,目前幻肢痛患者人数在不断增加,但发生机制还未完全阐明,治疗方法虽然不断更新但仍无重大突破.现就幻肢痛的研究进展作一综述.     

低剂量螺旋CT在青少年阻生牙诊断中的应用

目的 探讨低剂量螺旋CT在青少年口腔阻生牙诊断中的应用价值。方法 选择因阻生牙、多生牙或牙列不齐等口腔疾病在本院进行螺旋CT检查,并确诊为阻生牙的153例患儿为研究对象。按照口腔颌面部接受螺旋CT检查时的管电流时间乘积、扫描层厚度和准直器宽度3个参数不同进行分组:A组（n=30,330 mAs、6×0.75 mm和3.0 mm）,B组（n=30,140 mAs、6×0.75 mm和3.0 mm）,C组（n=30,80 mAs、6×0.75 mm和3.0 mm）,D组（n=31,80 mAs、6×1.50 mm和5.0 mm）及E组（n=32,50 mAs、6×1.50 mm和5.0 mm）。各组患者间性别与年龄等一般临床资料差异均无统计学意义（ P>0.05）。使用美国Victoreen公司的76-410高对比分辨率模体与76-421EX低对比分辨率模体（直径均为16 cm）,分别对各组螺旋CT检查结果的空间分辨率与密度分辨率进行评价。记录5组患儿进行螺旋CT检查时的剂量长度乘积（DLP）,计算CT的电离辐射剂量（有效剂量,ED）,并对ED值进行统计学分析,同时对图像质量评分进行比较。结果 ①各组CT图像的空间分辨率均为1.0 mm,密度分辨率分别为2.0、3.0、4.5、4.5及6.0 mm。② 5组间ED值差异有统计学意义（F=1 064.119, P=0.000）,E组患儿的ED值最低,为0.19 mSv,分别较A组、B组、C组和D组降低86.52％、67.24％、45.71％与38.71％。5组间任意两组ED值相比,差异均有统计学意义（ P<0.05）。③5组CT摄片按照CT图像清晰度质量等级评分标准的结果均≥3分,各组间差异无统计学意义（F=1.978, P>0.05）,且螺旋CT诊断结果与患者接受正畸手术的结果一致。结论 采用低剂量螺旋CT诊断阻生牙时,可获得满足临床诊断要求的CT图像质量,又可有效降低螺旋CT检查对患儿口腔颌面部的电离辐射剂量。低剂量螺旋CT可用于青少年阻生牙诊断。