Dual x-ray absorptiometry (DXA) provides a convenient, non-invasive method of assessing skeletal bone mineral which is widely used for clinical studies. This report describes a study to estimate the effective dose of radiation (ICRP-60 (1990)) to a typical female patient from scans performed on three DXA scanners: the Hologic QDR-1000, QDR-1000/W and QDR-2000. The scans modes studied were: total body; anteroposterior (AP) lumbar spine; lateral lumbar spine; proximal femur; distal forearm. An ionization chamber and tissue-equivalent phantom were used to determine entrance surface dose and percentage depth-dose curves for each scan mode. Anatomical data from ICRP-23 (Reference Man) and a body section atlas were used to estimate the absorbed dose to each organ in the scan fields. Effective dose was estimated using the ICRP-60 tissue weighting factors and the fraction of each organ in the scan field. Results are summarized below. Figures for the effective dose are given both excluding and (in brackets) including the ovaries to cover the cases of postmenopausal and premenopausal women respectively.
We assessed the value of bone scintigraphy combined with X-ray registration for the diagnosis and management of wrist pain in 65 patients. Studies were reported independently by two observers before and after registration. Registration improved localization of scan abnormalities in 53% (observer 1) and 61% (observer 2). In these patients, the bone scan contributed to the diagnosis independently of the X-ray in 37% and the management was altered in 31%. The value of the bone scan in the early diagnosis and management of wrist pain is increased when it is registered with X-rays.
Sacral tilt represented by a steeply angled superior endplate of S1 is associated with a significantly increased angle of lordosis, between L4 and S1, and pars fractures at L5. Steep angulation of the first sacral vertebral segment maybe the predisposing biomechanical factor that leads to pincer-like impingement of the pars interarticularis and then spondylolysis.
Absorptiometry provides a convenient, non-invasive method of measuring bone mass in the skeleton with high precision and low radiation dose to the patient (Tothill, 1989). Dual photon absorptiometry (DPA) based on the radionuclide source 153Gd was developed for measuring bone mineral density (BMD) at the clinically important sites of the spine and the hip (Wilson & Madsen, 1977). Recently, dual X-ray absorptiometry (DXA) has superseded DPA (Cullum et al, 1989). Compared with DPA, DXA has advantages of improved precision (coefficient of variation of 1% for spinal DXA compared with 2–3% for DPA) and shorter scanning times (6–8 min for DXA compared with 20–30 min for DPA) (Sorenson et al, 1989). Use of an X-ray tube instead of a radionuclide eliminates the problems associated with radioactive decay of the source (Lindsay et al, 1987). In the most recent development in DXA technology at least two manufacturers have introduced scanners based on a fan beam configuration coupled to a multidetector scanning head (Pommet et al, 1991; Steiger et al, 1991). Compared with the conventional configuration of a pencil X-ray beam linked to a single detector, scanning times are considerably shortened. In the instrument used for the study described in this report, the Hologic QDR-2000, fan beam scans of the lumbar spine (L1–L4) can be performed in either 1 min (sampling 5 lines cm−1 or 2 min (sampling 10 lines cm−1) depending on the precision required.
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