The practical management of artifact in computerised physiological data

Computerised physiological data contains artifact that needs to be identified and possibly removed. Whilst computers may eventually satisfactorily perform this function, at present only manual removal is possible for the majority of intensive care computer groups. We assessed the effects of artifact and its removal on the physiological data of 3 patients. Artifact was manually removed from 7 days of data in 4 parameters (heart rate, respiratory rate, systolic blood pressure [sbp] and transcutaneous oxygen [tcpO2]) by 3 independent observers. Six hour time periods were analysed. Median and mean values before and after the manual removal of artifact were compared. Overall. 6.5% of data was removed as artifact. This was greatest for tcp02 (9.9%) and sbp (10.6%), with smaller amounts for respiratory rate (2.8%) and heart rate (2.4%). Sbp showed a marked difference in the amount of data removed between patients, whereas tcp02 data contained quite large volumes of artifact, but this was fairly consistent between patients, Removal of artifact affected mean values more than median values. One observer considered that both physiological and non-physiological artifact should be removed, whereas the other two observers removed only non-physiological artifact. Agreement in results between the latter was good. Our results suggest that interobserver variability should have a minimal effect on values, once rules identifying the type of artifact to be removed are agreed. Removal of artifact did not have a clinically significant effect on results, but may be an important consideration in the statistical analysis of computerised physiological data.Abbreviations CPTM computerised physiological trend monitoring - tcp02 transcutaneous pressure of oxygen - sbp systolic blood pressure     

Do Textiles Impact DXA Bone Density or Body Composition Results?

External artifacts can confound dual-energy X-ray absorptiometry (DXA) measurements. It is often accepted that garments free of metal do not affect DXA results; however, little data exist in this regard. It is plausible that some textiles absorb radiation and thereby alter DXA results. We hypothesized that some dense or synthetic textiles, for example, reflective materials, might alter DXA-measured bone and soft tissue mass. Hologic and GE Lunar spine phantoms and a Bioclinica prototype total body phantom were imaged on a GE Lunar iDXA and Prodigy densitometer. Each phantom was scanned 10 times to establish mean values. Subsequently, 2 layers of various fabrics were placed over the entire top surface of the phantom, and 10 scans were performed without repositioning. Samples of natural, synthetic, or embellished fabric (including those with reflective material) and of varying thickness were used. Wilcoxon signed rank tests were used to compare the means between bare phantom and textile-covered phantom. Significant differences were demonstrated often, depending on the scanner, phantom, and textile used. A polyester fabric with reflective strip consistently altered measurements. For example, this fabric increased measured mean lumbar spine bone mineral density and total body bone mineral content by 0.008?g/cm² and 3.6?g, respectively (p?<?0.01). Similarly, mean total body fat decreased (?173 g) and lean mass increased (+213 g; p?<?0.01). Fat and lean mass were also affected by metallic thread, wool, blend denim, and shiny polyester (p?<?0.05), and lean mass was affected by cotton denim and sweatshirt material (p?<?0.0003). In conclusion, textiles can affect DXA-measured bone mineral density and body composition results. Even small amounts of reflective material could alter mass measurements by ~25% of the least significant change. Clothing made of dense textiles (e.g., wool and denim) or those with reflective material and metallic thread should be avoided during DXA scanning.     

Effect of ocular magnification on macular measurements made using spectral domain optical coherence tomography

Aim:

The aim of the present study was to study the effect of ocular magnification on macular measurements made using spectral domain optical coherence tomography (OCT).

Materials and Methods:

One hundred and fifty-one subjects were included from the normative study of foveal morphology carried out at our hospital. Subjects underwent comprehensive eye examination and macular scanning using Cirrus high-definition OCT and axial length (AXL) measurement. Macular cube 512 × 128 scan protocol was used for scanning the macula. Automated measurements of the fovea namely foveal diameter, foveal slope (lateral measurements) and foveal depth (axial measurement) were taken. A correction factor for ocular magnification was done using the formula t = p × q × s, where “t” is the corrected measurement, “p” is the magnification of OCT, “q” is the ocular magnification, and “s” is the measurement on OCT without correction. The difference between corrected and uncorrected measurements was evaluated for statistical significance.

Results:

Mean AXL was 22.95 ± 0.78 mm. Refractive error ranged from −3D to +4D. Mean difference between measured and corrected foveal diameter, slope and depth was 166.05 ± 95.37 µm (P < 0.001), 0.81° ± 0.53° (P < 0.001) and 0.05 ± 0.49 µm (P = 0.178) respectively. AXL lesser than the OCT calibrated value of 24.46 mm showed an increased foveal diameter (r = 0.961, P < 0.001) and a reduced foveal slope (r = −0.863, P < 0.001) than the corrected value.

Conclusion:

Lateral measurements made on OCT varied with AXL s other than the OCT calibrated value of 24.46 mm. Therefore, to estimate the actual dimensions of a retinal lesion using OCT, especially lateral dimensions, we recommend correction for the ocular magnification factor.     

Neuronal Responses in the Globus Pallidus during Subthalamic Nucleus Electrical Stimulation in Normal and Parkinson's Disease Model Rats

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) has been widely used as a treatment for the movement disturbances caused by Parkinson''s disease (PD). Despite successful application of DBS, its mechanism of therapeutic effect is not clearly understood. Because PD results from the degeneration of dopamine neurons that affect the basal ganglia (BG) network, investigation of neuronal responses of BG neurons during STN DBS can provide informative insights for the understanding of the mechanism of therapeutic effect. However, it is difficult to observe neuronal activity during DBS because of large stimulation artifacts. Here, we report the observation of neuronal activities of the globus pallidus (GP) in normal and PD model rats during electrical stimulation of the STN. A custom artifact removal technique was devised to enable monitoring of neural activity during stimulation. We investigated how GP neurons responded to STN stimulation at various stimulation frequencies (10, 50, 90 and 130 Hz). It was observed that activities of GP neurons were modulated by stimulation frequency of the STN and significantly inhibited by high frequency stimulation above 50 Hz. These findings suggest that GP neuronal activity is effectively modulated by STN stimulation and strongly dependent on the frequency of stimulation.     

Identifying electrode bridging from electrical distance distributions: A survey of publicly-available EEG data using a new method

ObjectiveEEG topographies may be distorted by electrode bridges, typically caused by electrolyte spreading between adjacent electrodes. We therefore sought to determine the prevalence of electrode bridging and its potential impact on the EEG literature.MethodsFive publicly-available EEG datasets were evaluated for evidence of bridging using a new screening method that employs the temporal variance of pairwise difference waveforms (electrical distance). Distinctive characteristics of electrical distance frequency distributions were used to develop an algorithm to identify electrode bridges in datasets with different montages (22–64 channels) and noise properties.ResultsThe extent of bridging varied substantially across datasets: 54% of EEG recording sessions contained an electrode bridge, and the mean percentage of bridged electrodes in a montage was as high as 18% in one of the datasets. Furthermore, over 40% of the recording channels were bridged in 9 of 203 sessions. These findings were independently validated by visual inspection.ConclusionsThe new algorithm conveniently, efficiently, and reliably identified electrode bridges across different datasets and recording conditions. Electrode bridging may constitute a substantial problem for some datasets.SignificanceGiven the extent of the electrode bridging across datasets, this problem may be more widespread than commonly thought. However, when used as an automatic screening routine, the new algorithm will prevent pitfalls stemming from unrecognized electrode bridges.     

肝脏扫查中斜切"伪像"的成因及对策

目的探讨将肝外毗邻脏器病变误诊为肝内病变的原因及防治措施。方法采取前瞻性的研究方法,对16例相关病例进行详细的超声检查（包括多切面比对、动态观察并结合呼吸运动）和随访。结果斜切时肿块完全映入肝内是导致误诊的原因,而纵切或横切可发现肿块与肝脏的界线,动态观察并结合呼吸运动,可进一步明确肿块与肝脏的关系。结论斜切“伪像”实际上是一种错觉。多切面扫查、动态观察并结合呼吸运动是防止斜切“伪像”,减少并杜绝此类误诊的关键。     

Magnetic resonance imaging evaluation after implantation of a titanium cervical disc prosthesis: a comparison of 1.5 and 3 Tesla magnet strength

Purpose

Cervical disc prostheses induce significant amount of artifact in magnetic resonance imaging which may complicate radiologic follow-up after surgery. The purpose of this study was to investigate as to what extent the artifact, induced by the frequently used Discover^® cervical disc prosthesis, impedes interpretation of the MR images at operated and adjacent levels in 1.5 and 3 Tesla MR.

Methods

Ten subsequent patients were investigated in both 1.5 and 3 Tesla MR with standard image sequences one year following anterior cervical discectomy with arthroplasty.

Outcome measures

Two neuroradiologists evaluated the images by consensus. Emphasis was made on signal changes in medulla at all levels and visualization of root canals at operated and adjacent levels. A “blur artifact ratio” was calculated and defined as the height of the artifact on T1 sagittal images related to the operated level.

Results

The artifacts induced in 1.5 and 3 Tesla MR were of entirely different character and evaluation of the spinal cord at operated level was impossible in both magnets. Artifacts also made the root canals difficult to assess at operated level and more pronounced in the 3 Tesla MR. At the adjacent levels however, the spinal cord and root canals were completely visualized in all patients. The “blur artifact” induced at operated level was also more pronounced in the 3 Tesla MR.

Conclusions

The artifact induced by the Discover^® titanium disc prosthesis in both 1.5 and 3 Tesla MR, makes interpretation of the spinal cord impossible and visualization of the root canals difficult at operated level. Adjusting the MR sequences to produce the least amount of artifact is important.     

医用扇形CT图像重建参数与产生伪影的分析

本文在理想CT系统的基础上,通过医用扇形CT图像重建参数与产生伪影的分析,指出了各种伪影与采集条件及重建参数的关系,目的是帮助医务工作者和维修工程师加深CT图像伪影的理解,以便采取更加有效的方法减少图像伪影。     

双能量CT单能谱成像技术在颅内动脉瘤夹闭术后的应用

目的 探讨Flash双能量CT单能谱成像技术去除颅内金属伪影用于颅内动脉瘤术后的临床应用价值.方法 对40例颅内动脉瘤术后复查的患者使用Flash双源CT双能量扫描,并以10 keV为间隔重组16组单能量图像.通过比较混合组和各keV组图像的客观指标伪影指数(AI)、对比噪声比(CNR)以及主观图像质量评分(4分法),寻找单能谱去金属伪影最佳的keV.结果 AI在120 keV时达最小,CNR在90 keV时最大,120 keV之后的单能谱图像的主观评分之间无明显差异.利用单能谱软件获得最佳单能量成像条件为90～ 120 keV,其图像均能满足诊断.结论 双能量单能谱成像技术能够有效去除金属伪影,清晰显示颅内动脉瘤术后的细微结构.