Musculoskeletal ImagingMagnification radiography
a method of achieving improved quality of images by use of contact exposure and fine-grain industrial films or direct
radiographic magnification. In the optical magnification technique radiation exposure is high; therefore, optical magnification should be used selectively when delineation of subtle abnormalities in the peripheral skeleton is important. In direct
radiographic magnification, a screen-film system and a microfocus
X-ray tube with a nominal
focal spot size of 100 mm are used, which may overcome some of the limitations of optical magnification, including the high radiation dose. However, direct
radiographic magnification should also be used selectively because of its potential to cause high radiation exposure.
Magnification radiography is used most frequently in the assessment of arthritis, hyperparathyroidism and infection.
In early rheumatoid arthritis, subtle erosive changes in sawtooth or a "dot dash" pattern are observed in the metacarpal head or ulnar styloid. The erosions seen in psoriatic arthritis and Reiters syndrome are characterized by bone proliferation with a fluffy appearance and linear periosteal new bone in the adjacent shafts of bones. Subtle calcifications in the hyaline cartilage and fibrocartilage in calcium pyrophosphate dihydrate crystal deposition disease may be detected only with high-resolution magnification techniques.
In hyperparathyroidism irregular resorption of the outer cortical margins is pathognomonic of the disease. Less specific is the finding of cortical striation or tunnelling.
In cases of osteomyelitis or septic arthritis magnification radiography may be helpful in delineating subtle cortical destruction or periosteal new bone before it can be demonstrated on conventional films.
Occasionally magnification radiography may also be helpful in delineating and defining subtle fractures, especially in the ribs, carpal scaphoid and femoral neck.
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