Computed Tomography, Second Edition

Excerpt

Since the release of the first edition of this book in 2003, x-ray computed tomography (CT) has experienced tremendous growth thanks to technological advances and new clinical discoveries. Few could have predicted the speed and magnitude of the progress, and even fewer could have predicted the diverse nature of the technological advancement. The second edition of this book attempts to capture these advances and reflect on their clinical impact.

The second edition provides significant changes and additions in several areas. The first major addition is a new chapter on radiation dose. In the last few years, significant attention has been paid to this subject by academic researchers, radiologists, the general public, and the news media. An increased awareness of the impact of radiation dose on human health has led to the gradual adoption of the “as low as reasonably achievable” (ALARA) principle, the implementation of American College of Radiology (ACR) accreditation and other dose reference levels, and the development of many advanced dose-saving features for CT scanners. The new Chapter 11 briefly describes some of the known biological effects of radiation dose, then presents different dose definitions and measurements, and concludes with an illustration of various dose-reduction techniques.

At the time the first edition was published, the term “multislice” CT was an accurate description of state-of-the-art scanners. Sixteen-slice scanners had just been introduced commercially, and their clinical utilities and advantages had just begun to be discovered. Since then, the “slice war” has continued, and now 64-, 128-, 256-, and 320-slice scanners are the new state of the art. These scanners can be easily labeled as “cone-beam” CT. They require not only a detector with wider coverage, but also other technologies such as new calibration techniques and reconstruction algorithms. Chapter 10 has been significantly expanded to discuss the technologies associated with these scanners and the new image artifacts created by them.

Since the first edition, CT advancement has not been limited to the technology. Advances also have been made in many areas of clinical applications, including the rapid development of cardiac CT imaging and new applications inspired by the reintroduction of dual-energy CT. Chapter 12 presents these advances and the fundamental physics and technologies behind them.

Image artifacts have accompanied x-ray CT ever since its birth over 30 years ago. Some artifacts are caused by the characteristics of the physics involved, some are caused by technological limitations, some are created by new technologies, some are related to the patient, some result from suboptimal design, and some are introduced by the operator. Chapter 7 has been expanded to reflect the ever-evolving nature of these artifacts and various efforts to overcome them.

Historically, CT advances were driven by the development of new hardware. However, it has become increasingly clear that hardware alone cannot solve all of the technical and clinical problems that CT operators face. The second edition includes significant updates to the section on statistical iterative reconstruction technology and presents some of the exciting new developments in this area.

To enhance readers' understanding of the material and to inspire creative thinking about these subjects, a set of “problems” concludes each chapter. Many problems are open-ended and may not have uniquely correct solutions. Hopefully readers will find these problems useful and will develop new problems of their own.

At the time of this writing, the world is experiencing an unprecedented financial crisis—that some call a financial “tsunami.” It is impossible to estimate or predict the impact of this crisis on the market for x-ray CT. However, CT technology is unlikely to remain stagnant. Many new exciting advances will take place in both the technology and its clinical applications.