Evidence-Based Imaging

Introduction

Over the past 2 decades, evidence-based medicine has become a dominant paradigm for understanding best practices in medicine. Simply put, evidence-based medicine is the explicit incorporation of the best research evidence into the care decision-making process. More formally, evidence-based medicine has been defined by Sackett and others as the incorporation of the best available evidence with physician judgment and experience and patient values and preferences. Evidence-based medicine should be distinguished from eminence-based medicine, typified by the seasoned professional using his or her best judgment and knowledge, without explicit review and incorporation of medical evidence. Implicit within evidence-based medicine is a process of identifying relevant evidence, critically appraising the evidence to identify and weight most heavily that which is methodologically most valid, and incorporating the best evidence into clinical care.

In the therapeutic arena, evidence-based medicine is generally focused on the choice between competing drugs or procedures to treat specific diseases. In this realm, randomized clinical trials are supreme as the research approach most likely to lead to unbiased estimates of the effectiveness of the various treatments. However, in diagnostics, including imaging, the process is more complex. Diagnostic tests do not directly affect clinical outcome, but rather that effect is mediated by treatment. In addition, randomized clinical trials are an inefficient means of understanding the performance of diagnostic tests. More commonly, diagnostic tests are evaluated based on cohort studies, where all patients get one or more imaging studies. However, as discussed in this chapter, such cohort studies are susceptible to a number of different biases, emphasizing the need for critical analysis. Screening introduces an additional set of biases that are difficult to avoid, compelling the use of randomized clinical trials to evaluate screening studies despite their relative inefficiency and large sample size requirement. Accordingly, evidence-based medicine applied to imaging, known as evidence-based imaging, has particular challenges in its application. However, despite its limitations, incorporation of evidence into imaging practice remains essential for the highest-quality clinical care.

Evidence-based imaging consists of identifying the relevant imaging literature for a specific clinical question, understanding the strengths and limitations of the existing evidence, and then incorporating that evidence into clinical care. The strength of evidence is based on the quality of the published studies, including the study size and potential for bias. Grading schemes are often used to categorize the strength of evidence as low or high. Because most radiologists do not directly order imaging studies, evidence-based imaging is, by nature, a collaborative process between radiologists and referring clinicians, incorporating the best evidence with patient values, and the experience of radiologist and clinician alike.

In this chapter, we discuss the critical analysis of the radiology literature to understand the methodological rigor of the published information. Second, we define how to incorporate evidence from the literature into an understanding of whether imaging will have value. Finally, in the third section, we explore how to apply evidence-based imaging in clinical practice and answer the critical question of whether imaging should be performed.