Arash Anvari

Statistics 101 for Radiologists

Diagnostic tests have wide clinical applications, including screening, diagnosis, measuring treatment effect, and determining prognosis. Interpreting diagnostic test results requires an understanding of key statistical concepts used to evaluate test efficacy. This review explains descriptive statistics and discusses probability, including mutually exclusive and independent events and conditional probability. In the inferential statistics section, a statistical perspective on study design is provided, together with an explanation of how to select appropriate statistical tests. Key concepts in recruiting study samples are discussed, including representativeness and random sampling. Variable types are defined, including predictor, outcome, and covariate variables, and the relationship of these variables to one another. In the hypothesis testing section, we explain how to determine if observed differences between groups are likely to be due to chance. We explain type I and II errors, statistical significance, and study power, followed by an explanation of effect sizes and how confidence intervals can be used to generalize observed effect sizes to the larger population. Statistical tests are explained in four categories: t tests and analysis of variance, proportion analysis tests, nonparametric tests, and regression techniques. We discuss sensitivity, specificity, accuracy, receiver operating characteristic analysis, and likelihood ratios. Measures of reliability and agreement, including κ statistics, intraclass correlation coefficients, and Bland-Altman graphs and analysis, are introduced.

CT-Guided Percutaneous Microwave Ablation of Tumors in the Hepatic Dome: Assessment of Efficacy and Safety

PURPOSE To evaluate the technique, efficacy, safety, and clinical outcomes of CT-guided microwave ablation of tumors in the hepatic dome. MATERIALS AND METHODS Retrospective review was conducted of 46 consecutive patients (31 men and 15 women; mean age, 64 y) treated with CT-guided microwave ablation for hepatic-dome tumors between June 2011 and December 2014. Baseline demographics of sex, tumor diagnosis, tumor location, tumor size, and technical details were recorded. Technical success was evaluated. Treatment response was assessed per European Association for the Study of the Liver criteria. Overall success and overall survival were calculated, and complications were recorded. RESULTS Forty-eight tumors were treated. Tumor locations included segments VIII (n = 32), VII (n = 10), and VIa (n = 6). Mean tumor size was 2.4 cm (range, 0.9-5.2 cm). Thirty-four tumors (70%) were treated following creation of artificial ascites with 0.9% normal saline solution (mean volume, 1,237 mL; range, 300-3,000 mL). The technical success rate was 100%, and the complete response rate was 94%. Overall survival rate was 73.9% over 24.7 months of follow-up. There were no major complications. Two patients experienced small, asymptomatic pneumothoraces that were aspirated at the time of the procedure and required no further treatment. CONCLUSIONS CT-guided microwave ablation of tumors in the hepatic dome is associated with a high technical success rate, high complete response rate, and low complication rate.

Clinical application of sonoelastography in thyroid, prostate, kidney, pancreas, and deep venous thrombosis

This article reviews the clinical applications of current ultrasound elastography methods in non-hepatic conditions including thyroid nodules, prostate cancer, chronic kidney disease, solid renal lesions, pancreatic lesions, and deep vein thrombosis. Pathophysiology alters tissue mechanical properties via ultrastructural changes including fibrosis, increased cellularity, bleeding, and necrosis, creating a target biomarker, which can be imaged qualitatively or quantitatively with US elastography. US elastography methods can add information to conventional US methods and improve the diagnostic performance of conventional US in a range of disease processes.

A Primer on the Physical Principles of Tissue Harmonic Imaging

Tissue harmonic imaging (THI) is a routinely used component of diagnostic ultrasonography (US). In this method, higher-frequency harmonic waves produced by nonlinear fundamental US wave propagation are used to generate images that contain fewer artifacts than those seen on conventional fundamental wave US tissue imaging. Harmonic frequencies are integer multiples of the fundamental frequency. The majority of current clinical US systems use second harmonic echoes for THI image formation. Image processing techniques (ie, bandwidth receive filtering, pulse inversion, side-by-side phase cancellation, and pulse-coded harmonics) are used to eliminate the fundamental frequency echoes, and the remaining harmonic frequency data are used to generate the diagnostic image. Advantages of THI include improved signal-to-noise ratio and reduced artifacts produced by side lobes, grating lobes, and reverberation. THI has been accepted in US practice, and variations of the technology are available on most US systems typically used for diagnostic imaging in radiologic practice. Differential THI is a further improvement that combines the advantages of THI, including superior tissue definition and reduced speckle artifact, with the greater penetration of lower frequency US, which permits high-quality harmonic imaging at greater depth than could previously be performed with conventional THI.

Ultrasound elastography: liver

Ultrasound elastography, also termed sonoelastography, is being used increasingly in clinical practice to aid the diagnosis and management of diffuse liver disease. Elastography has been shown to be capable of differentiating advanced and early-stage liver fibrosis, and consequently a major application in clinical liver care includes progression to cirrhosis risk stratification through (1) assessment of liver fibrosis stage in HCV and HBV patients, (2) distinguishing non-alcoholic steatohepatitis from simple steatosis in non-alcoholic fatty liver disease patients, and (3) prognostic evaluation of liver disease is autoimmune liver disease. In addition, elastographic characterization of focal liver lesions and evaluation of clinically significant portal hypertension have the potential to be clinically useful and are areas of active clinical research.

Navigational Guidance and Ablation Planning Tools for Interventional Radiology

Image-guided biopsy and ablation relies on successful identification and targeting of lesions. Currently, image-guided procedures are routinely performed under ultrasound, fluoroscopy, magnetic resonance imaging, or computed tomography (CT) guidance. However, these modalities have their limitations including inadequate visibility of the lesion, lesion or organ or patient motion, compatibility of instruments in an magnetic resonance imaging field, and, for CT and fluoroscopy cases, radiation exposure. Recent advances in technology have resulted in the development of a new generation of navigational guidance tools that can aid in targeting lesions for biopsy or ablations. These navigational guidance tools have evolved from simple hand-held trajectory guidance tools, to electronic needle visualization, to image fusion, to the development of a body global positioning system, to growth in cone-beam CT, and to ablation volume planning. These navigational systems are promising technologies that not only have the potential to improve lesion targeting (thereby increasing diagnostic yield of a biopsy or increasing success of tumor ablation) but also have the potential to decrease radiation exposure to the patient and staff, decrease procedure time, decrease the sedation requirements, and improve patient safety. The purpose of this article is to describe the challenges in current standard image-guided techniques, provide a definition and overview for these next-generation navigational devices, and describe the current limitations of these, still evolving, next-generation navigational guidance tools.

Reliability of Shear-Wave Elastography Estimates of the Young Modulus of Tissue in Follicular Thyroid Neoplasms

OBJECTIVE The purpose of this study is to determine the reliability of shear-wave elastographic estimates of the Young modulus in thyroid follicular neoplasms. SUBJECTS AND METHODS In this study, 35 adults with follicular nodules diagnosed by fine-needle aspiration (FNA) biopsy were enrolled. A single sonographer examined all nodules in three planes (sagittal, transverse, and transverse center). Two raters independently placed ROIs in each nodule. Intra- and interrater reliability were computed as intraclass correlation coefficients (ICCs) and were reported using the Guidelines for Reporting Reliability and Agreement Studies. RESULTS Thirty-five subjects with 35 follicular pattern nodules diagnosed by FNA biopsy were enrolled; 23 (65.7%) patients were female, with a mean age of 55.1 years (range, 23-85 years). For rater 1, intrarater agreement showed ICCs for single measurements of 0.87, 0.87, and 0.90 in the sagittal, transverse, and transverse center plans, respectively; ICCs for the median of multiple measurements were 0.97, 0.94, and 0.96 in the sagittal, transverse, and transverse center planes, respectively. For rater 2, intrarater agreement showed ICCs for single measurements of 0.94, 0.86, and 0.92 in the sagittal, transverse, and transverse center planes, respectively; ICCs for the median of multiple measurements were 0.97, 0.92, and 0.96 in the sagittal, transverse, and transverse center planes, respectively. Interrater agreement between measurements performed for the same subject showed ICCs for single measurements of 0.87, 0.87, and 0.80 in the sagittal, transverse, and transverse center planes, respectively; ICCs for the median of multiple measurements were 0.96, 0.93, and 0.92 in the sagittal, transverse, and transverse center planes, respectively. CONCLUSION ROI placement is a reliable method for estimating the Young modulus of tissue in follicular thyroid nodules.

A pilot study to precisely quantify forces applied by sonographers while scanning: A step toward reducing ergonomic injury

BACKGROUND There is a significantly high rate of work-related musculsokeletal injuries in sonography professionals. To date, assessment of risk factors for work- related injuries in sonographers has been based primarily on surveys, subjective reports, and observational methods. There is a need to develop quantitative techniques to better understand risk factors and develop preventive interventions. OBJECTIVE We pilot tested a high-resolution force-measuring probe capable of precisely measuring forces applied through the transducer by sonographers and used this novel direct measurement technique to evaluate forces during abdominal imaging. METHODS Twelve sonographers with varied experience, ranging from 1-33 years, performed routine abdominal scans on 10 healthy volunteers who had varied body mass indices (BMI). Imaging was conducted using the force-measuring probe, which provided real-time measurement of forces, and angles. Data were compared by sonographer years of experience and subject BMI. RESULTS In total, 47 abdominal examinations were performed as part of this study, and all images met standards for clinical diagnostic quality. The mean contact force applied across all exams was 8.2±4.3 Newtons (N) (range: 1.2-36.5 N). For subjects in the high BMI group (BMI>25, n = 4) the mean force was 10.5 N (range: 8.9-13.2 N) compared to 7.9 N (range: 5.9-10.9 N) for subjects with normal BMI (BMI = 18.5-25, n = 6). Similarly, the mean maximum force applied for subjects with high BMI (25.3 N) was significantly higher than force applied for subjects with normal BMI (17.4 N). No significant difference was noted in the amount of force applied by sonographers with more than 5 years of experience (n = 6) at 8.2 N (Range: 5.1-10.0 N) compared to less experienced sonographers (n = 6), whose forces averaged 8.1 N (Range: 5.8-10.0 N). CONCLUSIONS It is feasible to directly measure forces applied by sonographers using a high-resolution force measurement system. Forces applied during abdominal imaging vary widely, are significantly higher when scanning subjects with high BMI, and are not related to sonographer years of experience. This force measurement system has the potential to provide an additional quantitative data point to explore the impact of applied forces on sonographer related musculoskeletal injury, particularly in conjunction with various body positions, exam types and force durations.

Essentials of Statistical Methods for Assessing Reliability and Agreement in Quantitative Imaging

Quantitative imaging is increasing in almost all fields of radiological science. Modern quantitative imaging biomarkers measure complex parameters including metabolism, tissue microenvironment, tissue chemical properties or physical properties. In this paper, we focus on measurement reliability assessment in quantitative imaging. We review essential concepts related to measurement such as measurement variability and measurement error. We also discuss reliability study methods for intraobserver and interobserver variability, and the applicable statistical tests including: intraclass correlation coefficient, Pearson correlation coefficient, and Bland-Altman graphs and limits of agreement, standard error of measurement, and coefficient of variation.

Nonvascular Interventional Radiology

Advances in imaging capabilities and interventional tools have expanded the capabilities of interventional radiologists to diagnose and treat many genitourinary conditions. This chapter will focus on non vascular interventional procedures for the kidney.