1
What Is Clinical Imaging Physics?*

Ehsan Samei

Departments of Radiology, Medical Physics, Physics, Biomedical Engineering, and Electrical and Computer Engineering, Duke University Medical Center, Durham, NC, USA

1.1 Introduction

Medical imaging started with physics. Since November 8, 1895 when the German Physicist and first physics Nobel laureate Wilhelm Roentgen discovered the mysterious "x" rays, physics has had a central role in the development and continuous advancement of nearly every medical imaging modality in use today. Thus, the research role of physicists in the research and development of medical imaging is well established. The use of the images in the care of the patient has also been largely undertaken by interpreting physicians (mostly radiologists) who undergo years of specialized training to be qualified for the task. But what about clinical physics? Is there an essential role for the presence and contribution of physicists in the clinical practice of medical imaging? The answer is an obvious yes, but how is this role defined? What are the essential ingredients for effective contribution of medical physics to the clinical imaging practice? In this chapter we outline the basic components and expectation of quality physics support of clinical practice across the current medical imaging modalities (Table 1.1).

1.2 Key Roles of the Clinical Physicist

1.2.1 Offering "Scientist in the Room"

In recent years we have seen a drive toward evidence-based medicine [2], ensuring that clinical practice is informed by science. Physics is a foundational scientific discipline. Physicists are trained and skilled in the language and methods of science. Their perspective can thus play an essential role toward evidence-based practice. Likewise, the current emphasis on comparative effectiveness and meaningful use puts extra scrutiny on the actual, as opposed to presumed, utility of technology and processes [3-6]. This highlights the need for a scientific approach toward practice, again with an obvious role for physics. In line with these moves, medicine is also seeing a slow shift toward quantification, using biometrics that personalize the care of the patient in numerical terms [7]. This provides for better evidence-based practice for both diagnostic and interventional care. Again, physics is a discipline grounded in mathematics and analytics with direct potential for the practice of quantitative imaging. Finally, the mantra of value-based medicine [8] highlights new priorities for safety, benefit, consistency, stewardship, and ethics. To practice value-based care, the value needs to be quantified, which again brings forth the need for numerical competencies that physics can provide. Physicists have an essential role in the clinical imaging practice to serve as the "scientists in the room."

Table 1.1 Key expectations and activities of modern clinical imaging physics practice.

Attribute Practice

1. Offering "scientist in the room"

Providing scientific and quantitative perspective in the clinic toward evidence-based, quantitative, and personalized practice

1. Assurance of quality and safety

Assuring quality, safety, and precision of the imaging operation across complex sources of variability throughout the clinical practice

1. Regulatory compliance

Assuring adherence to practice for quality and safety regulatory requirements as well as guidelines of professional practice

1. Relevant technology assessment

Quantifying the performance of imaging technology through surrogates that can be related to clinical performance or outcome - evaluations performed in the context of acceptance testing and quality control

1. Use optimization

Prospectively optimizing the use of the imaging technology to ensure adherence to balanced performance in terms of dose and image quality

1. Performance monitoring

Retrospective auditing of the actual quality and safety of the imaging process through monitoring systems - quality control at the practice level; troubleshooting

1. Technology acquisition

Guidance on comparative effectiveness and wise selection of new imaging technologies and applications for the clinic

1. Technology commissioning

Effective commissioning of new imaging technologies and applications into the clinic to ensure optimum and consistent use and integration

1. Manufacturer cooperation

Serving as a liaison with the manufacturers of the imaging systems to facilitate communication and partnership in devising new applications

1. Translational practice

Engaging in quality improvement projects (clinical scholarship) and ensuring discoveries are extended to clinical implementation

1. Research consultancy

Providing enabling resources and advice to enhance the research activities involving medical imaging

1. Providing education

Providing targeted education for clinicians and operators on the technical aspects of the technology and its features

1.2.2 Assurance of Quality and Safety

The overarching reason for the presence of medical physicists in the clinic is to assure the quality and safety of the practice. Medical imaging devices are diverse and complex. Their heterogeneity manifests itself in their diversity of type, make and model, and technical parameters. Combined with the diversity in patients, human operators, and stakeholders of varying (sometimes competing) interests, the practice left on its own creates variability in the quality of care. This variability is not insignificant and has a cost. A recent report from the National Academy of Medicine reports most people will experience at least one diagnostic error in their lifetime [9]. In fact 10% of patient deaths and 6-17% of hospital adverse events are due to diagnostic errors. Medical imaging being largely a diagnostic process contributes to these statistics. The presence of clinical physicists in the clinic directly tackles this challenge. By overseeing the setup and use of the equipment and imaging processes, physicists offer an essential scrutiny of the operation to enhance consistency and minimize the likelihood of mishaps.

1.2.3 Regulatory Compliance

Toward the assurance of quality and safety, regulatory compliance and adherence to professional guidelines and standards offer a "scaffolding," a safeguard against quality issues that have been documented previously. Apart from federal and state regulation, The Technical Joint Commission (TJC), Centers for Medicare and Medicaid Service (CMS), Environmental Protection Agency (EPA), American College of Radiology (ACR), American Association of Physicists in Medicine (AAPM), and others provide useful standards, the meeting of which require active engagement of clinical imaging physicists. However necessary, the regulation and compliance-weighted focus of the current clinical physics practice may not be enough; the newest clinical practice guidelines from the ACR and AAPM highlight this limitation [10, 11]. Physics is most relevant to the extent that it seeks to address clinical needs and limitations. Regulations, by necessity and their reactive tendencies, are always a step behind clinical opportunities, needs, and realities. Clinical physics practice should extend beyond compliance and should inform the development and refinement of regulations and accreditation programs.

Figure 1.1 The three major components of clinical imaging physics practice according to the Medical Physics 3.0 paradigm. Attributes and assessment of technology (represented in the upper square) inform its optimum use (left square), and the two of them impact image outcome (right square). Outcome analysis conversely informs the optimum use of the technology.

1.2.4 Relevant Technology Assessment

The modern practice of clinical physics, as encouraged through the Medical Physics 3.0 paradigm [12], is based on three elements (Figure 1.1). One primary goal of clinical physics practice is technology assessment based on metrics that reflect the attributes of those technologies and relate to expected clinical outcomes. Toward that goal, the characterization of devices to ensure their adherence to vendor claims or regulatory guidelines is necessary but not enough; we must move from compliance-based to performance-based quality assurance. New physics practices should aim to devise and implement new metrics that are reflective of the performance of new technologies as well as the expected clinical outcome [12]. For example, characterizing...