Comparing cardiac ejection fraction estimation algorithms without a gold standard

RATIONALE AND OBJECTIVES: Imaging and estimation of left ventricular function have major diagnostic and prognostic importance in patients with coronary artery disease. It is vital that the method used to estimate cardiac ejection fraction (EF) allows the observer to best perform this task. To measure task-based performance, one must clearly define the task in question, the observer performing the task, and the patient population being imaged. In this report, the task is to accurately and precisely measure cardiac EF, and the observers are human-assisted computer algorithms that analyze the images and estimate cardiac EF. It is very difficult to measure the performance of an observer by using clinical data because estimation tasks typically lack a gold standard. A solution to this "no-gold-standard" problem recently was proposed, called regression without truth (RWT). MATERIALS AND METHODS: Results of three different software packages used to analyze gated, cardiac, and nuclear medicine images, each of which uses a different algorithm to estimate a patient's cardiac EF, are compared. The three methods are the Emory method, Quantitative Gated Single-Photon Emission Computed Tomographic method, and the Wackers-Liu Circumferential Quantification method. The same set of images is used as input to each of the three algorithms. Data were analyzed from the three different algorithms by using RWT to determine which produces the best estimates of cardiac EF in terms of accuracy and precision. RESULTS AND DISCUSSION: In performing this study, three different consistency checks were developed to ensure that the RWT method is working properly. The Emory method of estimating EF slightly outperformed the other two methods. In addition, the RWT method passed all three consistency checks, garnering confidence in the method and its application to clinical data.     

Estimating and comparing diagnostic tests' accuracy when the gold standard is not binary

RATIONALE AND OBJECTIVES: Investigators often need to assess the accuracies of diagnostic tests when the gold standard is not binary-scale. The objective of this article is to describe nonparametric estimators of diagnostic test accuracy when the gold standard is continuous, ordinal, and nominal scale. MATERIALS AND METHODS: A nonparametric method of estimating and comparing the area under receiver operating characteristic (ROC) curves, proposed by DeLong et al, is extended to situations in which the gold standard is not binary. Two examples illustrate the methods. RESULTS: Measures of diagnostic test accuracy, their variance, and tests for comparing two diagnostic tests' accuracies in paired designs are presented for situations in which the gold standard is continuous, ordinal, and nominal scale. These summary measures of diagnostic test accuracy are analogous in form and interpretation to the area under the ROC curve. CONCLUSION: Dichotomizing the outcomes of a gold standard so that traditional ROC methods can be applied can lead to bias. The methods described here are useful for assessing and comparing summary test accuracy when the gold standard is not binary scale. They have limitations similar to other summary indices.     

Estimating test-retest reliability in functional MR imaging I: Statistical methodology

A common problem in the analysis of functional magnetic resonance imaging (fMRI) data is quantifying the statistical reliability of an estimated activation map. While visual comparison of the classified active regions across replications of an experiment can sometimes be informative, it is typically difficult to draw firm conclusions by inspection; noise and complex patterns in the estimated map make it easy to be misled. Here, several statistical models, of increasing complexity, are developed, under which “test-retest” reliability can be meaningfully defined and quantified. The method yields global measures of reliability that apply uniformly to a specified set of brain voxels. The estimates of these reliability measures and their associated uncertainties under these models can be used to compare statistical methods, to set thresholds for detecting activation, and to optimize the number of images that need to be acquired during an experiment.     

Applying a statistical PTB detection procedure to complement the gold standard

This paper investigates a novel statistical discrimination procedure to detect PTB when the gold standard requirement is taken into consideration. Archived data were used to establish two groups of patients which are the control and test group. The control group was used to develop the statistical discrimination procedure using four vectors of wavelet coefficients as feature vectors for the detection of pulmonary tuberculosis (PTB), lung cancer (LC), and normal lung (NL). This discrimination procedure was investigated using the test group where the number of sputum positive and sputum negative cases that were correctly classified as PTB cases were noted. The proposed statistical discrimination method is able to detect PTB patients and LC with high true positive fraction. The method is also able to detect PTB patients that are sputum negative and therefore may be used as a complement to the gold standard.     

Diagnosis of paternity for cases without mother and without both mother and putative father based on blood group findings from the relatives

Summary Formulas of the estimated likelihood ratio Y/X are derived for cases without mother as well as those without both mother and putative father, by using blood group findings of their relatives.The distribution curves of the relative frequencies of log(Y/X) for these cases are calculated with respect to 10⁴ families which are created by a Monte Carlo simulation. The extent of success in the paternity diagnosis is clarified by the statistical analysis based on these distribution curves.According to the above analysis, fairly high chance of success can be obtained in the diagnosis of such ambiguous cases without the plaintive mother and/or the putative father, if their relatives are alive. It is also concluded that the genetic information as to the parents of the deceased person increases the exclusion probability, whereas that as to the spouse and children increases the fraction of log(Y/X) > 1 for non-father, corresponding to the fraction where the Essen-Möller value is less than 9%.     

卫生技术评估在医学影像中的应用现状及前景

医学影像技术的迅速发展与普及应用极大程度提高了国民健康水平,然而,伴随而来的医疗资源分布不合理、影像检查过度使用、诊断质量下降等问题严重损害了病人利益并造成国家资源浪费。卫生技术评估已成为世界发达国家制定卫生政策的重要参考,我国在这方面发展相对缓慢。通过回顾国内外卫生技术评估研究与其在医学影像中的应用现状,提出基于卫生技术评估理论与方法建立我国影像技术管理评价体系,对于指导资源合理配置、规范成像操作、提高诊断质量、促进影像技术决策转化具有重要意义。     

PET: a revolution in medical imaging

FDG-PET has had remarkable influence on the assessment of physiologic and pathologic states. The authors predict that FDG-PET imaging could soon become the most common procedure used by nuclear medicine laboratories and could remain so for an extended period of time. The power of molecular imaging lies in the vast potential for using biochemical and pharmacologic probes to extend applications arising from an understanding of cell biology to a large number of well-characterized pathologic states. Molecular imaging based upon tracer kinetics with positron-emitting radiopharmaceuticals could become the main source of information for the management of cancer patients. In that case, nuclear medicine procedures might become the most common imaging studies performed in the practice of medicine. This speculation is not farfetched when one realizes the enormous change that a single biologically important compound, FDG, has brought to the medical arena. The major challenge today is to attract the highly qualified individuals and to secure the resources needed to harness the opportunities in the specialty of molecular imaging.     

Calculating T2 in images from a phased array receiver

Images reconstructed from multielement, phased array coils and presented as the square root of the sum of the squares of the signals received by the individual elements have a distribution of signal and noise that distorts the relationship between the image intensity and the underlying signal. The distortion is accentuated for long echo times for which the signal‐to‐noise ratio (SNR) may be low. When measuring T₂ or T this signal distortion leads to biased estimates of these parameters. We demonstrate this effect and its dependence on the image SNR and the number of elements in a phased array coil. We evaluated the effects of four techniques for calculating T₂ from data acquired in phased array coils (log transform, least squares, lookup table correction, and maximum likelihood [ML] estimation). The ML estimation gave the most accurate T₂ in the presence of this bias. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

规范化应用影像学检查对乳腺疾病诊断价值的研究进展

研究证明乳腺X射线摄影和超声检查是乳腺疾病筛查的"黄金组合", MRI是乳腺疾病检查的重要补充, CT成像有待于技术的逐步成熟, 将成为诊断乳腺疾病的检查方法, SPECT对乳腺X射线摄影和超声不能确诊的患者可以提供较大帮助, PET/CT主要应用于乳腺癌的诊断及鉴别诊断、分期和疗效判断。目前尚没有一种影像学方法可以取代其他方法, 各种检查乳腺疾病的手段呈互补关系, 多种影像学方法融合已成为准确诊断和精确治疗的重要保障。笔者将阐述各种影像学检查方法在乳腺疾病诊断中的优点、局限性和诊断价值。     

建设新一代制式医院船的思考

在海军转型建设和装备发展加快之际,为了论证是否需要再建一艘新一代制式医院船的问题,本文围绕为什么要建和建成什么样的新一代制式医院船两个方面,对其必要性和设计要求进行了初步的分析和思考。     

General formulas of the estimated likelihood ratio Y/X in the diagnosis of paternity of a deceased putative father

Summary When the putative father is dead his probable genotype, essential for estimate of likelihood ratio in the diagnosis of paternity, should be deduced from his relatives. In the present paper are described the general method for such deduction of probable genotype and the derivation of the formula of likelihood ratio. 10⁴ examples of the diagnosis of paternity of deceased father are examined using a Monte Carlo method and the distributions of relative frequencies of log(Y/X) are calculated for the true father and non-father. These results indicate that the present method of estimation of Y/X from relatives is quite useful for the diagnosis of paternity of a deceased putative father.     

Interleaved echo planar imaging on a standard MRI system

This work describes an interleaved echo planar imaging (EPI) method for use on a standard whole body scanner. The data acquisition is divided into two to eight repetitions rather than one to two, as implemented by dedicated EPI systems. Interleaving allows the use of a lower sampling bandwidth with a significant increase in signal-to-noise. The method also has the advantages of relative ease of implementation, no need for postprocessing to remove image distortion, and no need for shimming on a case-by-case basis. The interleaved EPI method was applied to two applications ideally suited to EPI: breathhold T₂-weighted abdominal imaging and functional imaging. In vivo liver-lesion contrast as measured in a 35-patient study showed increased contrast for the Interleaved EPI by an average factor of 1.21 (± 0.34) over conventional spin-echo imaging. CNR measurements showed the EPI to be comparable with conventional spin echo with a relative factor of 1.00 (± 0.36). Functional imaging with an eight-shot interleaved EPI sequence provided 128 × 128 images of cerebral activation during bilateral finger tapping.     

全国医疗照射频度估算方法研究

目的 利用部分省份放射诊疗机构的调查数据,研究全国放射诊疗总频度的估算方法。方法 全国部分省份医疗照射频度水平委托调查涉及25个省份的557家放射诊疗机构。对数据进行了变量间的相关性分析、多重线性回归分析,比较包含不同变量组合的模型拟合效果。结果 医疗照射频度与门急诊人次、放射诊疗设备数量、放射工作人员数量之间存在大的相关性（|r|>0.5）。从调查数据中通过分层随机抽样,得到日均放射诊疗工作负荷的代表性样本。利用多重线性回归,建立放射诊疗总人次与门急诊人次、住院人次、放射诊疗设备数量、放射工作人员数量和医院级别之间的数学模型,并进行了模型诊断。估算2016年全国放射诊疗总人次为5.89亿。同时,采用稳健回归和中位数回归,对医疗照射频次进行了估算。结论 对全国放射诊疗总频度的估算有多种方法,建议采用随机抽样,结合统计和监测数据进行。样本的代表性十分重要,模型的指定和优化也需要更深入的研究。     

Constrained maximum likelihood estimation of the diffusion kurtosis tensor using a Rician noise model

A computational framework to obtain an accurate quantification of the Gaussian and non‐Gaussian component of water molecules' diffusion through brain tissues with diffusion kurtosis imaging, is presented. The diffusion kurtosis imaging model quantifies the kurtosis, the degree of non‐Gaussianity, on a direction dependent basis, constituting a higher order diffusion kurtosis tensor, which is estimated in addition to the well‐known diffusion tensor. To reconcile with the physical phenomenon of molecular diffusion, both tensor estimates should lie within a physically acceptable range. Otherwise, clinically and artificially significant changes in diffusion (kurtosis) parameters might be confounded. To guarantee physical relevance, we here suggest to estimate both diffusional tensors by maximizing the joint likelihood function of all Rician distributed diffusion weighted images given the diffusion kurtosis imaging model while imposing a set of nonlinear constraints. As shown in this study, correctly accounting for the Rician noise structure is necessary to avoid significant overestimation of the kurtosis values. The performance of the constrained estimator was evaluated and compared to more commonly used strategies during simulations. Human brain data were used to emphasize the need for constrained estimators as not imposing the constraints give rise to constraint violations in about 70% of the brain voxels. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

计算机X射线摄影剂量指示值与受检者入射体表剂量的关系

目的 研究计算机X射线摄影(CR)中剂量指示值与受检者入射体表剂量之间的关系,建立受检者入射体表剂量的估算方法。方法 以Kodak的CR系统为研究对象,基于理论推导建立受检者入射体表剂量估算模型,通过实验测量确定模型中的重要参数,建立由剂量指示值估算入射体表剂量的方法,并通过实验验证其有效性。结果 用本研究建立的模型计算出的受检者入射体表剂量与实测值之比的平均值为0.97,95%可信区间为0.77~1.18;在比较不同X射线摄影系统时,发现计算值与实测值之间的差异没有统计学意义。 结论 本研究建立的由剂量指示值估算受检者入射体表剂量的模型,可用于快速评估计算机X射线摄影所致受检者的入射体表剂量。     

Managing radiation use in medical imaging: a multifaceted challenge

This special report aims to inform the medical community about the many challenges involved in managing radiation exposure in a way that maximizes the benefit-risk ratio. The report discusses the state of current knowledge and key questions in regard to sources of medical imaging radiation exposure, radiation risk estimation, dose reduction strategies, and regulatory options.     

Estimation of time of death by quantification of melatonin in corpses

A method for the estimation of time of death (TOD), was evaluated by measuring the melatonin (MT) content of pineal bodies (PBs), sera and urine samples from 85 cadavers. A total of 44 cadavers were investigated in Sapporo (geographical coordinates N 43° 4, E 141° 21) and 41 in Tokyo (N 35° 39, E 139° 44). MT contents were measured by radioimmunoassay (RIA) in 75 PBs, 27 sera and 14 urine samples. Exponential differences of pineal MT content were recognized between peaks in nighttime and nadirs in daytime, ranging from 0.099 to 63.2 ng/PB. Circadian rhythms were also observed for the concentrations of MT in serum (11–205 pg/ml), and in urine (7.5–137.5 pg/ml). Consequently, criteria for the TOD estimation are proposed as follows. 1) Pineal MT contents — (1) 0–0.2 ng/PB: TOD 1100–1700 hours, (2) 0.2–0.3 ng/PB: TOD 0700–2000 hours, (3) 0.3–1 ng/PB: inconclusive, (4) 1–4 ng/PB: TOD 1600–1000 hours, (5) 4–8 ng/PB: TOD 2000–0800 hours, (6) over 8 ng/PB: TOD 2000–0500 hours, 2) Serum MT concentration — (1) 0–100 pg/ml: inconclusive, (2) over 100 pg/ml: TOD 2200–0100 hours, and 3) Urinary MT concentration — (1) 0–35 pg/ml: inconclusive, (2) over 35 pg/ml: TOD 1800–0600 hours. The range of the estimation can be limited by a combination of these 3 criteria. The present method can be combined with other methods for estimating the TOD to decrease the range.