The hypertransradiant hemithorax: the importance of lateral decentring, and the explanation for its appearance due to rotation

Experimental evidence is presented indicating that 80% of the increase in unilateral film blackening on the chest radiograph resulting from rotation of the patient is due to asymmetrical absorption of the X-ray beam. Scatter contributes 20% to this increase in blackening. The effect on the radiograph of lateral decentring is also described. In the rotated patient, the hypertransradiant hemithorax always occurs on the side to which the patient is rotated, and is independent of the projection. If this rule is broken, then decentring or a thoracic abnormality is present.     

An improved method for sacro-iliac joint imaging: a study of normal subjects, patients with sacro-iliitis and patients with low back pain

A new method is described for quantitative measurement of the uptake of 99mTc--methylene diphosphonate (MDP) by the sacro-iliac joints. The method uses 'regions of interest' providing advantages over the previously described 'slice' method; the two methods are compared in normal subjects, patients with known sacro-iliitis and patients with low back pain. Sacro-iliac activity, as calculated by the sacro-iliac index (SII) in normal patients, was shown to decrease with age in females but not in males. The SII was compared with radiographs of the sacro-iliac joints in the patients with known sacro-iliac joint disease and in those with low back pain. The method is useful for the exclusion of sacro-iliitis as a specific cause of back pain.