Customer Reviews

Fuchs's Radiographic Exposure, Processing and Quality Control

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This book is written for a non-technical audience and provides a collection of rules of thumb based on practical experience but not on rigorous understanding of fundamentals. Many simplifications go too far and some explanations are outright misleading. By reading this book, a radiology tech may glean a few tips to produce a good radiograph on most systems. Yet the book may lead to fallacious intuitions. This book should not be used to gain accurate practical understanding of the physics and system design principles in radiography.

The practical rules in the book will probably work fairly well in most cases for conventional systems. New digital imaging systems may render even the practical tips obsolete since they are based on practical experience with conventional systems and not on fundamentals.

Here are some of the most egregious fallacies:

Page 10 states that radiographic images are formed thanks to the polychromatic nature of the x-ray beam: "If all of the x-rays were of the same energy, the image would be extremely poor, essentially a silhouette." In reality, the opposite is true -- a monochromatic beam with all photons carrying the same energy would provide the best image quality (tissue contrast) with best patient dose efficiency (at appropriate keV). Tissue differentiation is produced by differential attenuation of photons in tissues, even if all the photons carry identical energies. X-ray system designers go to great lengths to reduce the polychromaticity of the x-ray beam.

Page 59 states that with the doubling of the number of atoms in some space, the likelihood of x-rays hitting an atom when passing through the space also doubles. Wait a minute! What if the original likelihood of hitting an atom was 70%? Will that probability go to 140% when the number of atoms is doubled in that space? Of course, this description is incorrect. Doubling the number of atoms in a given volume will square the likelihood of the x-ray photon passing through the volume.

On page 129, the author states that "Excessive filtration in the beam defeats the purpose of exposing the radiograph. When density losses become visible, they necessitate an increase in the mAs to compensate. Such an increase in mAs simply reintroduces additional patient skin dose, which the filters were added to eliminate. ...an optimum level of protective filtration has been established to achieve maximum level of protection for the patient without affective the radopgrahic density." In reality, no such optimal level can be established. Increasing the filtration will always reduce skin dose from a polychromatic source (x-ray tube) even after the mAs is increased to maintain proper film exposure. Additional spectral filtration equivalent to 2.5 mm of aluminum is simply required by safety regulations. Anything above that is an improvement. The only limitation to adding more spectral filtration is the increased x-ray tube loading and the tube's limited maximum output. This error is particularly disturbing because it cause one to miss opportunities to reduce patient dose while improving image quality when extra mAs can be afforded or to choose to purchase a system that is less dose efficient.

The book's lack of rigor leads to the example on page 154 which states that "bone stops 40 x-rays for every x-ray stopped by soft tissue." In reality, the linear attenuation coefficient of bone is at most 2 or 3 times higher than that of soft tissue at typical x-ray energies.