Patient dose in morphometric X-ray absorptiometry.
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Absorptiometry, Photon↗
Biomedical subjects
G M Blake
Publications and source records attributed to G M Blake.
Measurements of broadband ultrasonic attenuation in the calcaneus in premenopausal and postmenopausal women.
We report a study of broadband ultrasonic attenuation (BUA) in the calcaneus in 248 women. Measurements were performed with a Walker-Sonix UBA-575 ultrasonic bone analyser. The populations studied were 15 healthy young volunteers (group 1, mean age 26 years), 200 healthy pre- and postmenopausal women (group 2, mean age 53 years) and 33 osteoporotic women with vertebral crush fractures (group 3, mean age 66 years). Subjects in group 1 each had 10 repeated measurements of their right heel. Duplicate BUA measurements in the right heel were performed in 96 subjects and bilateral scans in a further 87 women in group 2. The remaining 17 subjects in group 2 and those in group 3 had a single scan of the right heel. All women in groups 2 and 3 had dual X-ray absorptiometry (DXA) scans of the lumbar spine and femoral neck. The precision study on the women in group 1 gave a root mean square (RMS) coefficient of variation (CV) of 4.2%. Individual CV results showed statistically significant differences (range 1.3%-7.6%). Duplicate scans in subjects in group 2 gave a RMS CV of 4.6% while the bilateral measurements showed no significant difference between the two heels. Linear regression analysis gave the following relationship between BUA and age: BUA = 87.1 - 0.76 (Age - 40) dB/MHz (r = -0.31, p less than 0.001, SEE = 14.0 dB/MHz). Multivariate regression analysis showed that, in addition to age, years since the menopause was also a significant factor in predicting BUA.(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
The effect of vertebral collapse on spinal bone mineral density measurements in osteoporosis.
Bone mineral density (BMD) of the lumbar spine (L1-L4) was measured using dual-energy x-ray absorptiometry (DXA) in 57 postmenopausal women with spinal osteoporosis aged 50-82 years (average age 64). For each vertebra between L1 and L4, the BMD was compared to age-matched normal population values and a Z score obtained. Twenty three patients had between one and three collapsed vertebrae from L1 to L4. The average Z score for fractured vertebrae was -1.62 but for uncollapsed vertebrae was -2.26 (P less than 0.001). The difference in Z scores obtained for collapsed and uncollapsed vertebrae was greater where only one fracture was present (0.803) compared to two (0.577) or three fractures (0.245). The average increase in density for a fractures vertebra was 0.070 g/cm2. For L1 vertebral fractures alone the average increase in BMD was 0.096 g/cm2, L2 vertebral fractures 0.041 g/cm2, L3 fractures 0.029 g/cm2 and L4 fractures 0.062 g/cm2. It is concluded that as vertebral collapse is not alway detected using DXA and usually causes a rise in BMD, spinal x-rays are necessary to avoid misinterpretation of a falsely elevated BMD in osteoporotic patients, particularly in longitudinal studies or when monitoring therapy, where small changes in BMD are important.
Absorptiometry, Photon↗
Postmenopausal screening for osteopenia.
Dual energy X-ray absorptiometry (DXA) measurements of bone mineral density (BMD) in the lumbar spine and femoral neck have been performed in 1000 consecutive women aged between 40 and 60 years referred for screening for osteopenia. A detailed history was taken from each woman that included relevant lifestyle parameters and known risk factors for osteoporosis. After exclusions, e.g. because of fractures, corticosteroid or prolonged HRT use, 627 women (mean age 53 years) were considered suitable for further analysis. The mean BMD in the lumbar spine (L1-L4) was 0.946 g/cm2 and in the femoral neck was 0.767 g/cm2. Significant correlations were found between BMD and years after the menopause and weight (range r = 0.20-0.24). However, these parameters are not reliable enough predictors of BMD to be of value in clinical practice. If osteopenia is to be the basis for initiating prophylactic measures against bone loss, then a threshold BMD must be chosen below which treatment will be advised. Since the correlation coefficient between spinal and femoral neck BMD measurements was only 0.64, assessment of any individual requires consideration of both sites. There is as yet no consensus as to the number of women who may require to be treated and we have provided BMD values that identify a range of population sizes (the lowest 20, 30, 40 and 50 percentiles). It should be noted that there was a 16% loss of BMD in the spine and 14% in the femoral neck during the first 5 years after the menopause.(ABSTRACT TRUNCATED AT 250 WORDS)
Absorptiometry, Photon↗
A comparison of three commercially available PET imaging systems.
Three commercial positron emission tomography (PET) imagers were assessed using the same test protocol (Positron Corporation 'Posicam', Siemens Ecat 951/31 and the Scanditronix PC 4096-15WB). A cylindrical phantom and a 'Jaszczak' phantom both filled with 18F were employed to measure sensitivity, slice uniformity, transaxial and axial resolution and cold rod contrast. The spread of results were as follows: sensitivity varied from 2.08 to 3.73 kcps kBq-1 ml-1 (77-138 kcps microCi-1 ml-1); radial resolution on axis (at 17.5 cm) varied from 5.0 to 5.9 mm (6.7-8.1 mm); tangential resolution ranged from 5.4 to 5.8 mm (6.7-8.6 mm); axial resolution ranged from 4.6 to 11.5 mm (6.6-13.6 mm); contrast in the middle of a 30 mm diameter rod varied from 98 to 93% and for a 5 mm rod from 37 to 22%. The performance of all three systems approximated reasonably well to the manufacturers' published specifications. The most significant differences were found to be in sensitivity, axial resolution and deadtime correction and can be explained by the choice of crystal size and crystal/photomultiplier configuration.
Evaluation Studies as Topic↗
Compliance with hormone replacement therapy (HRT) after screening for post menopausal osteoporosis.
OBJECTIVE: To assess compliance with recommendations for hormone replacement therapy (HRT) in postmenopausal women following screening for osteoporosis. DESIGN: A postal questionnaire sent to women an average of 8 months (range 6-12) following measurement of their bone mineral density (BMD), and recommendations regarding HRT given to the referring general practitioner. SETTING: Referrals from local general practitioners. Mixed social class. SUBJECTS: 400 postmenopausal women aged 40-69 years (average age 52). MAIN OUTCOME MEASURES: Compliance with advice and if failing to comply, reasons for not doing so. RESULTS: Replies were received from 352 women (88%) and 74% of respondents followed advice to start, continue, or refrain from starting or continuing HRT with regard to protecting their skeleton. Those who rejected advice to take HRT mostly had concern over side effects or the efficacy or safety of treatment. Of the women who started HRT 28% subsequently stopped, the principal reasons being withdrawal bleeding and weight gain. Of the women recommended to take HRT, 39% were not taking treatment by 8 months after referral, either because they ignored advice given (22%) or because of side effects (17%). CONCLUSIONS: Screening leads to increased usage of HRT among women at most risk for osteoporosis. However, almost 40% of women with low bone mineral density were not taking HRT 8 months after referral, and therefore until improved compliance has been demonstrated screening cannot be widely recommended.
Aged↗
Fracture thresholds in osteoporosis: implications for hormone replacement treatment.
The bone mineral densities of the lumbar spine and femoral neck were determined by dual energy chi ray absorptiometry in 110 women aged 40-82 years (average 65 years) with spinal osteoporosis who had had at least one atraumatic vertebral compression fracture and in 1026 normal women aged 40-79 years (average 52 years). The women with osteoporosis showed a significant decrease in bone mineral density (BMD) at the lumbar spine and femoral neck compared with age matched normal women (sixth decade of life -26% spine, -23% femoral neck; seventh decade -26% spine, -16% femoral neck). The fracture threshold, defined as the 90th centile of spinal BMD for women with osteoporosis, was 0.81 g/cm2 at the lumbar spine and 0.656 g/cm2 at the femoral neck. Five per cent of normal women aged 40-49 years, 20% aged 50-59 years, and 45% aged 60-69 years had a BMD below this threshold. To maintain the bones of women above the fracture threshold until the age of 70 years about 50% of postmenopausal women need hormone replacement therapy. However, if the BMD is to be kept above the fracture threshold for a women's lifetime, e.g. until the age of 80-90 years, then most women will need treatment, though for various lengths of time depending on their initial BMD. Measurements of BMD in postmenopausal women currently help in identifying the risk of osteoporotic fractures but in the lifetime assessment of risk in a single subject they may have a more important role in deciding the duration of hormone replacement therapy.
Absorptiometry, Photon↗
Measurement of forearm bone mineral density in normal women by dual-energy X-ray absorptiometry.
We report the results of forearm measurements, without the use of a water bath, using dual-energy X-ray absorptiometry (DEXA) in 100 normal women aged 29-69 years (average age, 52 years). Studies were performed using the Hologic QDR-1000, with bone mineral density (BMD) measured at three sites in the non-dominant forearm: ultradistal, distal one-third and a region between these two. The precision of the technique was 0.74%, 0.55% and 0.58%, respectively. The normal range for forearm BMD and variation with age was established. BMD was also measured in the lumbar spine (L1-L4) and femoral neck. Linear regression analysis gave a range of correlation coefficients between forearm and axial sites of r = 0.49-0.67. Standard errors of the estimate (SEE) in predicting axial from peripheral measurements gave average values from the three forearm sites of 0.085 g/cm2 for the femoral neck and 0.118 g/cm2 for the spine. Forearm measurements using DEXA can now be reliably performed in air. DEXA produces a high-resolution image, is fast and simple to perform, and enables both cortical and trabecular sites to be examined in one measurement. Forearm and axial measurements can be performed using the same equipment, where centres possess a suitable DEXA system.
Absorptiometry, Photon↗
Comparison of radionuclide estimation of glomerular filtration rate using technetium 99m diethylenetriaminepentaacetic acid and chromium 51 ethylenediaminetetraacetic acid.
Simultaneous measurements of the clearance rates of technetium 99m diethylenetriaminepentaacetic acid (99mTc-DTPA) and chronium 51 ethylenediaminetetraacetic acid (51Cr-EDTA) were performed in 30 patients with a range of renal function (glomerular filtration rates between 9 and 120 ml/min). Using multiple blood samples, the two clearance values correlated well (r = 0.991, standard error 3.9 ml/min), but DTPA clearance was systematically higher by 7.6%. For each radiopharmaceutical, an equation was derived to correct clearance values obtained using only plasma samples taken at 2 and 4 h for the systematic error inherent in this technique compared with analysis of the complete plasma concentration-time curve. The root mean square error remaining after application of these equations was 1.9 ml/min for both the EDTA and DTPA data. The corresponding errors obtained using the equation derived by Brochner-Mortensen for EDTA plasma clearance were 2.2 ml/min and 1.9 ml/min, respectively, these values were not significantly different from those obtained using the equations derived in this study.
Adult↗
The effect of positioning on dual energy X-ray bone densitometry of the proximal femur.
The influence of subject repositioning on the precision of bone mineral densitometry of the proximal femur using dual energy X-ray absorptiometry was estimated by determining the variation in the bone mineral density (BMD) of subjects scanned with their foot and leg position varying from that routinely used in clinical scanning. The mean variations in BMD of the femoral neck, Ward's triangle and trochanter were 2.7, 4.1 and 1.7%, respectively, in eight subjects scanned with the foot internally rotated by 0, 13 and 27 degrees. The mean variations in BMD in four subjects scanned with the leg in the customary position and abducted +/- 6 degrees from the conventionally used scanning position were 3.6, 2.8 and 1.6% for the same respective regions of interest. For diagnostic applications, the orientation of the leg and foot during scanning is relatively unimportant since the variations in BMD introduced by the different foot and leg orientations likely to be encountered in routine clinical scanning are small compared to the intrapopulation variation in BMD. However, for monitoring changes in BMD longitudinally, careful repositioning of the foot and leg will be necessary to achieve precision in vivo of less than 1%.
Absorptiometry, Photon↗
Intersite comparison of the Hologic QDR-1000 dual energy X-ray bone densitometer.
UNLABELLED: We have compared results from 13 Hologic QDR-1000 bone densitometers: (i) by performing spine and hip scans on two normal volunteers; (ii) by acquiring sets of 10 sequential scans on a Hologic anthropomorphic spine phantom. For each QDR-1000 site visited a set of spine phantom scans was also acquired on a QDR-1000 at Guy's Hospital to serve as a control study. All scans were analysed using the Hologic scan comparison software. Radiographers at each site were asked to perform their own independent analysis of the scans of the two volunteers. The precision of the bone mineral density (BMD), bone mineral content (BMC) and projected area (Area) results for a set of 10 phantom scans was 0.11%, 0.14% and 0.12% respectively. The coefficient of variation (CV) between sites for the sets of phantom scans was 0.58% for BMD, 0.71% for BMC and 0.35% for Area. In comparison, CVs for the phantom scans acquired on a single QDR-1000 were 0.23%, 0.23% and 0.09% respectively. The CV for the BMD results on the two volunteers obtained using the scan comparison software averaged 1.4% for the spine and 2.1% for the femoral neck. The CV for the results obtained by site radiographers averaged 2.2% for the spine and 3.7% for the femoral neck. Significant differences in the technique used for hip analysis were found. CONCLUSIONS: (i) differences in calibration between systems were generally less than 1%; (ii) variations in results resulting from differences in analytical technique were more significant than those resulting from differences in calibration.
Absorptiometry, Photon↗
Pharmacokinetics, biodistribution and dosimetry of 99Tcm(V)DMSA in humans with squamous cell carcinoma.
Technetium-99m (99Tcm)(V) dimercaptosuccinic acid (DMSA) is a new tumour imaging agent which has been used to evaluate squamous carcinoma (SCC) of the head and neck. This study evaluated the pharmacokinetics and biodistribution of 99Tcm(V)DMSA in patients with SCC and calculated the bone mass of a New Zealand White (NZW) rabbit. This data was then used to calculate the effective dose equivalent in man. A total of 16 patients were studied (5 with no tumour, 11 with tumour). 99Tcm(V)DMSA had a fast bi-exponential blood clearance in patients with no tumour (30 and 401 min) and patients with tumour (30 and 387 min) with no significant difference (p greater than 0.05) between the two groups. 99Tcm(V)DMSA had a fast cumulative urine excretion with mean half-times in non-tumour and tumour patients of 183 min and 244 min respectively. There was no significant difference (p greater than 0.05) between these two latter groups. The effective dose equivalent of 99Tcm(V)DMSA in man is 5.1 microSv/MBq.
Aged↗
89Sr therapy: strontium plasma clearance in disseminated prostatic carcinoma.
Strontium plasma clearance is an important factor determining the absorbed dose to metastases and bone marrow in patients receiving 89Sr radionuclide therapy for metastatic bone disease. Amongst male patients with disseminated prostatic carcinoma, the renal component of strontium clearance is frequently greatly reduced compared with values reported for healthy middle aged men. We report a study of renal and gut strontium plasma clearance, renal function, calcium urinary excretion, parathyroid function and extent of skeletal osteoblastic metastatic disease in patients referred for radiostrontium therapy for metastasised prostatic malignancy. The wide variation in net strontium clearance was principally due to variation in the renal component. Low values of strontium renal clearance were found to correlate with the elevation of serum PTH and nephrogenous cyclic AMP, which in turn correlated with extent of skeletal metastatic disease. This suggests that the osteosclerotic metastases characteristic of prostatic carcinoma induce secondary hyperparathyroidism due to the high avidity of the skeleton for calcium. The resulting reduction in strontium excretion may be beneficial to the objectives of radiostrontium therapy.
Bone Neoplasms↗
Measurements of the strontium plasma clearance rate in patients receiving 89Sr radionuclide therapy.
The total strontium plasma clearance rate due to excretion through the kidneys and gut has an important influence on the absorbed does delivered to skeletal metastases and red bone marrow in patients receiving 89Sr radionuclide therapy for disseminated prostatic carcinoma. Although a measurement of the renal strontium plasma clearance rate may readily be obtained through a 24-h urine collection, little information is available on the correlation between renal and total clearances. We describe a method of determining total strontium plasma clearance rate from whole body counter measurements of total body strontium retention and measurements of plasma strontium concentration following administration of a 85Sr tracer dose at the time of 89Sr therapy. Amongst the 26 patients whom we studied, the total clearance rate varied from 1.2-15.0 l/day, renal clearance rate from 0.1-11.5 l/day, and the mean gut clearance rate was 2.0 l/day. A close correlation was found between total and renal clearance, with the renal component accounting for 96% of the variance in total strontium plasma clearance. A weak collection may exist between gut and renal clearance.
Humans↗
Glomerular filtration rate and the kinetics of 123I-metaiodobenzylguanidine.
We have recently reported evidence that the calcium antagonist nifedipine can improve the tumour retention of 131I-metaidobenzylguanidine (131I-MIBG) in patients with malignant phaeochromocytoma. During studies of the pharmacological modification of tumour MIBG kinetics, it is important to distinguish clearly between a direct effect on MIBG cellular retention by a pharmaceutical, and secondary effects due, for example, to a change in glomerular filtration rate (GFR). In order to provide the fundamental kinetic data required for the numerical modelling of the effect of nifedipine on tumour MIBG kinetics, we have investigated the influence of GFR on MIBG plasma and renal kinetics. The 123I-MIBG plasma curve and MIBG renal plasma clearance rate were studied in ten patients, ranging from subjects without biochemical or scintigraphic evidence of phaeochromocytoma to individuals with widely disseminated metastatic disease. GFR was measured using the 99mTc-DTPA plasma clearance method. In four cases, the studies were repeated with the patients taking oral nifedipine. Statistically significant correlations were found between GFR and the MIBG plasma concentration. MIBG renal plasma clearance rate and the early (0 to 5 min) renal excretion of MIBG. The data permit the evaluation of the plasma integral during the first few min following bolus injection, a quantity important in the numerical modelling of tumour kinetics. GFR was found to have a major influence on whole-body MIBG kinetics, but there was also evidence of the effect of the metastatic tumour burden.
3-Iodobenzylguanidine↗
Strontium-89: treatment results and kinetics in patients with painful metastatic prostate and breast cancer in bone.
Two hundred and two patients with bone pain from metastatic cancer were treated with 40 microCi/kg of Sr-89. Patients were followed with pain diaries, records of medication taken, sleep patterns, serial bone scans and a Karnofsky Index. One hundred and thirty-seven patients with adequate followup survived at least 3 months, including 100 with prostate and 28 with breast carcinoma. Eighty of the 100 patients with prostate cancer responded, and 25 of the 28 breast cancer patients improved. Ten patients with prostate cancer and five with breast cancer became pain free. Little hematologic depression was noted. Sr-89 kinetic studies showed that strontium taken up in osteoblastic areas remained for 100 days. The tumor-to-marrow absorbed dose ratio was 10:1.
Bone Neoplasms↗
Modification by nifedipine of 131I-meta-iodobenzylguanidine kinetics in malignant phaeochromocytoma.
Following a case report that oral nifedipine can suppress the secretion of noradrenaline by phaeochromocytoma, we examined the effect of nifedipine on the tumour kinetics of tracer 131I-meta-iodobenzylguanidine (131I-mIBG) in five patients referred for mIBG radionuclide therapy for disseminated malignant phaeochromocytoma. In one subject a striking modification of mIBG kinetics was found that resulted in a doubling of the absorbed dose to tumour while the patient was taking nifedipine. At the same time, urinary excretion of noradrenaline was suppressed by a factor of three. The effect of nifedipine in this patient was confirmed when tracer studies were repeated nine months later. The changes in tumour kinetics were shown to be due to prolonged retention of mIBG rather than increased tumour blood flow or alteration of the curve of mIBG plasma concentration as a function of time.
3-Iodobenzylguanidine↗
The pharmacokinetics of selenium in psoriasis and atopic dermatitis.
The pharmacokinetics of [75Se-L]-selenomethionine was studied in 10 patients with psoriasis, 10 with atopic dermatitis and 10 healthy subjects. Values for the gut absorption and the rate of endogenous excretion of [75Se-L]-selenomethionine, the exchangeable total-body selenium and plasma selenium concentration showed no significant differences between either patient group and the controls. The results suggest that there is no gross abnormality of selenium pharmacokinetics in either disease, and fail to explain why previous studies have found reduced selenium concentrations and selenium-dependent glutathione peroxidase activity in psoriasis and atopic dermatitis.
Adult↗