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Introduction

Exploring Essential Radiology helps medical students and residents develop their imaging interpretation skills in various modalities as well as various anatomical regions. This book offers the chance for learners to sharpen their clinical knowledge and diagnostic skills.

X-Rays

Production

Radiographs are produced by beaming x-rays through the body onto a medium (film or digital solid-state plate). The patient is properly positioned and protected from unnecessary radiation, the medium and x-ray sources are correctly placed, optimal x-ray machine settings are selected, and the radiograph is interpreted and reported.

Radiodensity

X-rays passing through the body tissues are recorded as black on the radiograph; those that are absorbed or deflected leave the medium white—this reduction in intensity of the x-ray beam is attenuation. Living tissues cause different degrees of attenuation (the tissue radiodensity). Tissues are grouped into four degrees of radiodensity—air, fat, soft tissue, and bone. Metal within the body produces a fifth degree of radiodensity. Air is radiolucent and appears black, while bone is radio-opaque and appears white. Between different radiodensities are radiological interfaces. They can be seen as lines parallel to the x-ray beam.

Views

Images of the same structure can be looked at from different angles, termed views. Radiographs (being two-dimensional) must be taken in at least two projections at right angles to obtain a three-dimensional mental image. Views are named according to the direction of the beam (anteroposterior, posteroanterior, lateral, or oblique). At times, special views may be ordered, such as skyline patella, stress inversion, bone age, skeletal survey, weight-bearing, or views taken with joints in the full range of movement (such as the neck in flexion and extension).

Image Properties

The degree of penetration of the medium determines the viewer's ability to identify different tissues; thus, an over-penetrated film is too black, and an underpenetrated film is too white. Sharpness is an indicator of how well defined the various tissue interfaces are; low resolution indicates the degree of blurring of the interfaces. Spatial resolution is the capacity to define two small objects close together. X-rays, being divergent, will magnify objects in their path—the closer an object is to the medium, the less is its magnification. Overlap of structures in the x-ray path is termed superimposition, and anatomical knowledge is required to interpret the overlapping images of complex structures. Problems with superimposition are partially resolved by ...

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