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PubMed2004

A triage strategy based on clinical risk factors for selecting elderly women for treatment or bone densitometry: the EPIDOS prospective study.

A triage strategy, based on a clinical hip fracture risk score, may be used to classify elderly women into three groups: one at high risk and requiring treatment, another needing further assessment by bone densitometry, and a third at low risk. We used prospective data from the EPIDOS study (7512 women older than 75 years and followed for an average of 3.9 years) to assess the potential value of such a strategy for identifying elderly women with a hip fracture risk twice the cohort average (i.e. > or =20 per 1000 woman-years). An individual fracture risk score was calculated with the final risk function (Cox model). To compare this strategy with systematic BMD measurement and with current European recommendations, we examined the number of high-risk women identified, their average risk levels, sensitivity for hip fracture, and the number of high-risk women who need to be treated to prevent one hip fracture (hypotheses: all identified women are treated; sensitivity is equal to the point estimate; treatment reduces fracture risk by 35%). A triage strategy based on age, fracture history since the age of 40 years, body mass index, number of instrumental activities of daily living for which assistance is needed, grip strength, and visual acuity can identify 20% of the cohort as at high risk, 75% of them from clinical factors only, and the rest after BMD measurements (threshold: -2.5 T-score). The triage strategy would be significantly more sensitive than systematic BMD screening (51 versus 35%) and would require many fewer BMD examinations (10%). Compared with current recommendations, triage would identify fewer women (20 versus 28%) but at a significantly higher average risk of hip fracture (30 versus 20 per 1000 woman-years). Fewer high-risk women would be treated to prevent one hip fracture (29 versus 41) and fewer bone densitometry tests would be needed (10% versus 54%). The proposed triage strategy may be a useful clinical tool for selecting elderly women for treatment or bone densitometry.

Activities of Daily Living↗
PubMed2005

Reliability and accuracy of vertebral fracture assessment with densitometry compared to radiography in clinical practice.

Absorptiometry of the thoraco-lumbar spine at the time of bone densitometry to detect vertebral deformities consistent with fracture is now available. The performance of absorptiometry in clinical practice compared to radiography has not been fully established, especially in the presence of osteoarthritis or scoliosis. Our first objective was to compare absorptiometry to radiography for detection of vertebral deformity in elderly women who were referred for bone densitometry with or without scoliosis or disc space osteoarthritis excluded. Our second objective was to assess the effect of osteoarthritis and scoliosis on the inter-rater reliability of both technologies. The study group comprised two hundred five women age 65 and older referred for bone densitometry in a large multispecialty group practice. Lateral and antero-posterior (AP) absorptiometry images and lateral spine radiographs were obtained on all participants. The vertebrae on all images were evaluated for vertebral deformity by two observers according to the Genant semiquantitative criteria who were blinded to each other's readings. Disc spaces were evaluated on radiographs for osteoarthritis. Absorptiometry AP images were evaluated for scoliosis. In the absence of scoliosis, the sensitivity and specificity of absorptiometry for persons with one or more radiographic grade 2-3 deformities (>25% reduction of vertebral height) for the two readers were 87-93% and 93-95%, respectively. The inter-rater reliability of absorptiometry improved in the absence of moderate or severe disc space osteoarthritis. A strategy of absorptiometry with follow-up radiography only in those with scoliosis or apparent grade 2 deformity accurately identifies those with prevalent grade 2 or 3 deformity on radiography (accuracy 0.98 and kappa 0.86 for reader 1; accuracy 0.99 and kappa 0.92 for reader 2). Lateral and AP absorptiometry imaging of the spine with selective follow-up radiography accurately identifies elderly women with vertebral deformity consistent with moderate or severe fracture, but extra caution is necessary when evaluating vertebrae in the presence of adjacent disc space osteoarthritis.

Absorptiometry, Photon↗
PubMed1999

Validation of the simple calculated osteoporosis risk estimation (SCORE) for patient selection for bone densitometry.

Bone densitometry using dual energy X-ray absorptiometry (DXA) is the 'gold standard' for osteoporosis diagnosis. However, mass screening for osteoporosis has not been recommended, and no consensus has been reached regarding specific targeted screening programs. Recently, the Simple Calculated Osteoporosis Risk Estimation (SCORE) was developed to identify postmenopausal women likely to have low BMD (< or > -2.0 SD of the young adult normal), who may be selected for DXA testing. This instrument uses a case-selective approach to screen for osteoporosis by summing a score based on: age, race, rheumatoid arthritis, history of nontraumatic fracture over 45 years of age, estrogen use, and weight. In our study, SCORE was validated using 398 postmenopausal women at least 45 years of age residing within 50 km of Toronto, Ontario, Canada (one of 9 centers of the Canadian Multicentre Osteoporosis Study, a national population-based study). At the recommended threshold of 6, SCORE had a sensitivity of 90%, specificity of 32% and a positive predictive value of 64%. From receiver operating characteristic (ROC) analysis, no threshold identified SCORE as a useful instrument in our population; area under the ROC curve was 0. 71. Specificity of the SCORE is poor; at the recommended threshold of 6, 68% of those with normal bone mineral density (BMD) would be selected for bone densitometry. Development and validation of SCORE by Lydick and colleagues may have been confounded by the nature of the study sample; sampling from specialty clinics; and by the choice of outcome, combining data from different DXA machines, and using only data from the femoral neck to identify low BMD. A simple and effective approach to select patients for bone densitometry has yet to be established.

Absorptiometry, Photon↗
PubMed2001

Prediction of osteoporotic fractures by bone densitometry and COLIA1 genotyping: a prospective, population-based study in men and women.

Osteoporosis is a common disease with a strong genetic component, characterized by reduced bone mineral density and increased fracture risk. Although the genetic basis of osteoporosis is incompletely understood, previous studies have identified a polymorphism affecting an Sp1 binding site in the COLIA1 gene that predicts bone mineral density and osteoporotic fractures in several populations. Here we investigated the role of COLIA1 genotyping and bone densitometry in the prediction of osteoporotic fractures in a prospective, population-based study of men (n = 156) and women (n = 185) who were followed up for a mean (+/- SEM) of 4.88+/-0.03 years. There was no significant difference in bone density, rate of bone loss, body weight, height, or years since menopause between the genotype groups but women with the 'ss' genotype were significantly older than the other genotype groups (p = 0.03). Thirty-nine individuals sustained 54 fractures during follow-up and these predominantly occurred in women (45 fractures in 30 individuals). Fractures were significantly more common in females who carried the COLIA1 's' allele (p = 0.001), although there was no significant association between COLIA1 genotype and the occurrence of fractures in men. Logistic regression analysis showed that carriage of the COLIA1 's' allele was an independent predictor of fracture in women with an odds ratio (OR) [95% CI] of 2.59 [1.23-5.45], along with spine bone mineral density (OR = 1.57 [1.04-2.37] per Z-score unit) and body weight (OR = 1.05 [1.01-1.10] per kilogram). Moreover, bone densitometry and COLIA1 genotyping interacted significantly to enhance fracture prediction in women (p = 0.01), such that the incidence of fractures was 45 times higher in those with low BMD who carried the 's' allele (24.3 fractures/100 patient-years) compared with those with high BMD who were 'SS' homozygotes (0.54 fracture/100 patient-years). We conclude that in our population, COLIA1 genotyping predicts fractures independently of bone mass and interacts with bone densitometry to help identify women who are at high and low risk of sustaining osteoporotic fractures.

Absorptiometry, Photon↗
PubMed1997

Influence of spondylopathy on bone densitometry using dual energy X-ray absorptiometry.

Spinal cord injury (SCI), as well as other neuromuscular disorders, not only results in osteopenia but also induces various patterns of osseous, articular, and soft tissue alterations. In the spinal column, a variety of abnormalities occur. To evaluate the magnitude of discrepancy of bone densitometry results caused by spondylopathy in SCI patients, we analyzed anteroposterior (AP) radiographs of the lumbar spine [obtained within 1 month of dual energy X-ray absorptiometry (DXA)] in 116 SCI patients for various manifestations of spondylopathy, and matched the result to each vertebral level (L1, 2, 3, 4). The dataset was stratified by individual vertebra (totally 463 vertebrae) as valid (no demonstrable other abnormal density on plain radiograph except osteopenia), abnormal without, and abnormal with hardware. The influence of spondylopathy on bone densitometry results was determined by the analysis of variance (ANOVA) and post hoc analysis. Our results showed that 227 (49%) vertebrae were abnormal. Significant elevation (15%, 15%, 18%, 20%; P < 0.001-P < 0.05) of bone mineral density (BMD; g/cm2) was observed at all levels (L1, 2, 3, 4, respectively), particularly at those abnormal vertebrae without hardware compared with valid (no other abnormal density on radiograph except osteopenia (Table 1). The L4 level was most severely affected. We concluded that in SCI patients, owing to various secondary progressive skeletal abnormalities, particularly neuropathic spondylopathy, can have strongly and significantly elevated vertebral bone densitometry results, which can obscure underlying osteoporosis, leading to misinterpretation and underestimation of fracture risk. DXA, although characterized by improving spatial resolution, cannot replace radiography in establishing the magnitude of this skeletal pathology. Therefore, determination of bone density in this region with corresponding plain radiographs is highly recommended.

Absorptiometry, Photon↗
PubMed2004

Bone densitometry in a patient with hypophosphatemic osteomalacia.

A 60-year-old Caucasian woman with a 1-year history of pain at the ribs, spine, and pelvis consulted at our Institute in March 1999. She brought a bone densitometry performed using a Lunar DPX densitometer that showed bone mineral density (BMD) measurements in the osteoporotic range at both the lumbar spine and the femoral neck. As a child she had had bowed legs and had been treated with ultraviolet radiation. Results of the laboratory test performed at our institute showed normal total serum calcium, repeated low serum P levels, and a low renal phosphate threshold with elevated total and bone fraction of alkaline phosphatase with normal intact parathyroid hormone (PTH). A diagnosis of hypophosphatemic osteomalacia due to renal phosphate leak was made. She began treatment with neutral sodium phosphate at 1.5 g/day and calcitriol 0.5 microg/day. Her serum P levels normalized, and there was a progressive decrease in alkaline phosphatase levels. The densitometry showed a very rapid increase in BMD values with normalization at the lumbar spine after 10 months of treatment. This case shows the importance of bone densitometry in the follow-up of patients with suspected osteomalacia.

Alkaline Phosphatase↗
PubMed1991

Edge detection versus densitometry for assessing coronary stenting quantitatively.

The optimal method used to analyze quantitatively the immediate angiographic results of coronary stenting in the coronary arteries has not been studied. Accordingly, minimal luminal cross-sectional area was determined by 2 methods, edge detection and densitometry, in 19 patients who underwent percutaneous transluminal coronary angioplasty (PTCA) and then coronary stent implantation for symptomatic coronary stenoses. The correlation coefficient, 0.73 before angioplasty, decreased to 0.59 after coronary angioplasty and then increased to 0.83 after stent implantation. The mean differences between edge detection and densitometric determinations of minimal luminal cross-sectional area were 0.31 +/- 0.51 mm2 before PTCA, -0.38 +/- 1.22 mm2 after angioplasty and 0.35 +/- 0.79 mm2 after coronary stenting. It is concluded that, although the correlation and variability in the measurement of minimal luminal cross-sectional area between edge detection and densitometry deteriorate after PTCA, they are improved after stenting, probably because of smoothing of the vessel contours by the stent and remodeling of the stented segment into a more circular configuration. Therefore, in the stented coronary artery, edge detection and densitometry are equally acceptable methods of analysis.

Absorptiometry, Photon↗
PubMed2006

The analysis of densitometry image of bone tissue based on computer simulation of X-ray radiation propagation through plate model.

In this work, we have presented an attempt at the computer modelling of the attenuation effect of X-ray radiation which occurs in the densitometry test. The purpose of the modelling is to examine the extent to which the parameters of the plate model of bone tissue affect bone mineral density (BMD) parameter. In the modelling the fundamental functions realised by a densitometry device have been taken into consideration. Certain necessary assumptions simplifying the computation of the complex physical processes that occur during the transition of X-ray radiation through an object have been made. In order to compute the image produced by interaction of radiation the attenuation law is applied. The modelling of an object consists in defining its dimensions and its material characteristics. In the presented simulation the material characteristics of the object are limited to its attenuation coefficient. A different value of the coefficient can be defined for each voxel. The result image is produced by the calculation of partial attenuation in the individual voxels. The levels of grey in the image represent the value of the computed radiation intensity which is recorded in the "detector" after transition through the object. The simulation has been performed for the plate model representing trabecular bone tissue with 0.1mm porosity compartments. The results of the simulation of the plate model are presented. It can be observed that for certain modelled porosity compartments the size, structure and spatial arrangement are not properly recorded in the two-dimensional "detector". The recorded simulation results may be found useful for explaining difference that has been noticed between the BMD obtained from the densitometry test and the bone susceptibility to fracture.

Absorptiometry, Photon↗
PubMed1999

Computed tomography densitometry of the lung: a method to assess perfusion defects in acute pulmonary embolism.

OBJECTIVE: To evaluate the potential of spiral computed tomography (CT) densitometry of the lung to assess segmental perfusion defects in patients with acute pulmonary embolism. MATERIALS AND METHODS: Ten patients with known segmental or lobar perfusion defects on ventilation/perfusion scintigraphy and with normal findings in the contralateral lung segment underwent spiral CT of the thorax before and after the administration of contrast material. Regions of interest were defined in 14 segments with normal perfusion and in 14 segments with reduced perfusion. Three consecutive densitometry measurements were performed in each segment. RESULTS: Those segments with reduced perfusion showed a significantly lower mean CT value on the enhanced scans (-813.4 +/- 57.1 Hounsfield units (HU) vs -794.0 +/- 44.8 HU, P = 0.01) and a significantly decreased contrast enhancement (12.3 +/- 18.2 HU vs 29.8 +/- 16.6 HU, P <0.01) when compared to segments with normal perfusion. Measurements from the unenhanced CT scans were not statistically different between segments with reduced and normal perfusion. CONCLUSIONS: Spiral CT densitometry allows the assessment of at least segmental perfusion defects in patients with acute pulmonary embolism.

Absorptiometry, Photon↗
PubMed1996

Assessment of renal function with computed tomographic densitometry measurements.

RATIONALE AND OBJECTIVES: We assessed the relationship between multiple renal computed tomographic (CT) densitometry parameters and renal function. METHODS: Three hundred seventy-three patients underwent standardized helical CT of the abdomen. The ratio of mean attenuation in the renal cortex to mean attenuation in the aorta (KAR), the products of mean renal cortical attenuation with CT-estimated renal volume (KVP), and the patient's weight (KWP) were derived from scans obtained 90 sec (n = 373) and 30 sec (n = 108) after initiation of intravenous contrast material administration. These densitometry parameters were compared with renal function measured by serum level of creatinine and creatinine clearance (CrCl). RESULTS: Among the 373 patients in the study, we found statistically significant differences (p < .01) between the patients with normal renal function (CrCl > or = 60 ml/min, n = 300) and the patients with abnormal renal function (CrCl < 60 ml/min, n = 73) for the KAR, KVP, and KWP. The KAR was the parameter best correlated with CrCl and was an independent predictor of renal function from the patient's age, weight, and renal volume. Fifty-three patients with a KAR less than 1 had significantly worse renal function (CrCl = 60 +/- 21 ml/min) than the patients with a KAR greater than or equal to 1 (CrCl = 95 +/- 31 ml/min). Only 4% of patients with normal renal function had a KAR less than 1. A threshold value of KAR less than 1 had a sensitivity of 55%, a specificity of 96%, a positive predictive value of 75%, and a negative predictive value of 90% for predicting renal dysfunction. CT parameters obtained at 30 sec were less useful than parameters at 90 sec. CONCLUSION: In patients undergoing clinically requested CT scanning, renal densitometry analysis can be used to depict patients with normal renal function; however, it has a high false-negative rate in depicting patients with diminished renal function.

Absorptiometry, Photon↗
PubMed2003

The use of densitometry to detect differences in bone mineral density and content of live White Leghorns fed varying levels of dietary calcium.

Densitometry was investigated as a noninvasive tool to monitor skeletal integrity in live White Leghorns as an indicator for osteoporosis, a noninfectious disease resulting in mineral loss from the bone. The objectives of the experiment were 1) to assess the ability of densitometry to detect differences in bone integrity in live White Leghorns fed varying concentrations of dietary calcium and 2) to correlate densitometric scans with other bone test methods and production parameters that are sensitive to calcium concentrations in the diet. Hens were fed hypercalcemic (5.4%), control (3.6%), or hypocalcemic (1.8%) diets from 32 to 58 wk of age. A Norland densitometer was used to assess bone mineral density (BMD) and bone mineral content (BMC) of the left tibia and humerus in restrained, unanesthetized hens at 36, 46, and 56 wk of age (experiment 1) and at 38, 48, and 58 wk of age (experiment 2). Bones were excised from hens at 38, 48, and 58 wk of age for breaking strength measurements. Results from the densitometric scans showed that BMD and BMC of the humerus and tibia of live hens decreased linearly when hens consumed diets with decreasing concentrations of calcium (experiment 2). Similar trends in BMD and BMC were detected in experiment 1 at 36 wk of age using BW as a covariate. The results from the densitometric scans were comparable to those obtained from other bone tests commonly used. For example, bone breaking force, stress, and modulus of elasticity decreased linearly as hens consumed decreasing concentrations of calcium. Bone breaking force was correlated with BMD (r=0.65, P<0.001). We concluded that densitometry accurately measures differences in BMD and BMC in live birds fed varying concentrations of dietary calcium.

Absorptiometry, Photon↗
PubMed2002

Current controversies in bone densitometry.

In the face of increasing use of all types of bone densitometry in the diagnosis and management of osteoporosis, the limitations of the World Health Organization criteria for the diagnosis of osteoporosis based on bone density measurements have become apparent. Controversy has arisen about whether these criteria should be used for the diagnosis of osteoporosis. Using densitometry to monitor changes in bone density as a measure of therapeutic efficacy has been criticized. It has been suggested that changes in bone density are not surrogates for reduction in fracture risk and that regression to the mean invalidates serial testing. There is both truth and fallacy in these controversies. The resolutions are critical to the role of densitometry in clinical practice.

Absorptiometry, Photon↗
PubMedDate not supplied

Influence of temperature on QCT: implications for mineral densitometry.

OBJECTIVE: Inaccuracies in quantitative CT (QCT) for vertebral bone mineral measurements may result from differences between the temperature of the vertebrae and the calibration standards. This study aims to quantify these effects by using scans of marrow-equivalent materials and computer simulation. MATERIALS AND METHODS: The CT numbers of fat, water, gelatin suspension, and bone were measured within an anthropomorphic phantom at temperatures between -18 and 38 degrees C. A computer simulation was then performed using these materials to represent marrow fat, soft tissue, and bone in varying proportions over this temperature range. Postprocessing single and dual energy QCT calculations were then performed on the data acquired from the simulation. RESULTS: A change of 80 HU in the CT number of water on cooling from 38 to -18 degrees C was demonstrated. An increase of 95 HU in the CT number of fat occurred over the same temperature range. Dry cortical bone showed no change in CT number with temperature changes from 24 to -18 degrees C. In the computer simulation, the fat error associated with single energy QCT for trabecular bone mineral densitometry was 20% less for specimens at room temperature than at body temperature. In simulated frozen specimens, varying marrow fat/soft tissue composition had almost no effect on single energy QCT mineral densitometry. Dual energy QCT methods that use a fat-equivalent reference material were significantly influenced by the temperature of the specimen. CONCLUSION: The fat error of single energy QCT for mineral densitometry may have been underestimated in previous in vitro studies using vertebral specimens scanned at room temperature. In the simulation, the fat error diminished as the temperature of the specimen was reduced and was negligible when frozen. Fat-equivalent reference materials used for dual energy QCT in vivo should have similar X-ray-attenuating properties at room temperature to those of marrow fat at body temperature.

Absorptiometry, Photon↗
PubMedDate not supplied

Detection of central pulmonary embolism on computed tomography densitometry images before computed tomography pulmonary angiography.

OBJECTIVE: The purpose of this article is to describe the imaging findings of acute central pulmonary embolism on computed tomography (CT) densitometry images performed before contrast-enhanced CT pulmonary angiography. METHODS: A retrospective review was conducted of reports from all CT pulmonary angiograms performed at our institution, and cases of acute central pulmonary embolism, defined as those with clot in the main, left, or right pulmonary arteries, were identified. Images of positive studies were reviewed on a picture archiving and communications system (PACS) workstation. RESULTS: A total of 1282 CT pulmonary angiograms were obtained for evaluation of possible acute pulmonary embolism, and 1 combined CT aortogram and pulmonary angiogram was performed for aortic dissection and acute pulmonary embolism. Two hundred fourteen (16.7%) examinations positive for acute pulmonary embolism were identified, 26 (12.1%, 2.0% of total examinations) of which had central clots. Of the 26 patients with central acute pulmonary embolism, 12 (46.1%, 5.6% of all positive studies and 0.9% of all CT pulmonary angiograms) had clots that were visible on the densitometry images. CONCLUSION: Although an uncommon finding, acute central pulmonary embolism can be detected on CT densitometry performed to optimize opacification of the pulmonary arteries for CT pulmonary angiography and may prove useful in selected clinical situations.

Acute Disease↗
PubMed2004

An analysis of an open access general practitioner bone densitometry service.

General practitioners (GPs) are increasingly involved in the selective opportunistic case finding of osteoporosis and treatment of this condition. An open access bone densitometry service has existed for GPs in the Cardiff area since 1993. The purpose of this study was to assess the effectiveness of this service, particularly with respect to the appropriateness of bone densitometry requests and the impact of the service on hospital outpatient referrals. Over a period of 12 months, 560 patients were referred to the open access service by 154 GPs. A total of 229 (41%) patients were given a clinical diagnosis of osteoporosis. Four hundred and seventy-three (84%) referrals followed the clinical referral criteria. In 85% of cases, GPs claimed that they would have referred patients to the hospital outpatient department, if there were no open access bone densitometry service. The majority of the referrals were appropriate, and the service appears to have reduced GP referrals to the specialist clinic.

Absorptiometry, Photon↗
PubMed1993

In vitro analysis of urinary calculi: type differentiation using computed tomography and bone densitometry.

Thirty-six urinary stones were studied by computed tomography and bone densitometry in order to find a correlation between the chemical composition of the stones and the densitometric data. In vitro, the more common cases of lithiasis can be divided into 3 main groups: uric acid, cystine and the calcium salts, e.g. calcium oxalate monohydrate, calcium oxalate dihydrate and calcium phosphate. Struvite stones fall between the second and third groups. Computed tomography and bone densitometry can differentiate between the groups, provided that the value of the "stone mineral or calcium content" is correlated with the true calculated volume of the stone (resulting in the specific stone density) instead of the projection area (resulting in the area density). This is only possible in vitro. The in vivo application of these technologies in the treatment of stones of unknown composition could provide important information, but major restrictive factors pose difficulties. Further clinical studies are necessary, especially to define the role of bone densitometry.

Absorptiometry, Photon↗
PubMed2004

Comparison of radiographic texture analysis from computed radiography and bone densitometry systems.

Osteoporosis is a disease that results in an increased risk of bone fracture due to a loss of bone mass and deterioration of bone structure. Bone mineral density (BMD) provides a measure of bone mass and is frequently measured by bone densitometry systems to diagnose osteoporosis. In addition, computerized radiographic texture analysis (RTA) is currently being investigated as a measure of bone structure and as an additional diagnostic predictor of osteoporosis. In this study, we assessed the ability of a peripheral bone densitometry (PD) system to yield images useful for RTA. The benefit of such a system is that it measures BMD by dual-energy x-ray absorptiometry and therefore provides high- and low-energy digital radiographic images. The bone densitometry system investigated was the GE/Lunar PIXI, which provides 512 x 512 digital images of the heel or forearm (0.2 mm pixels). We compared texture features of heel images obtained with this PD system to those obtained on a Fuji computed radiography (CR) system (0.1 mm pixels). Fourier and fractal-based texture features of images from 24 subjects who had both CR and BMD exams were calculated, and correlation between the two systems was analyzed. Fourier-based texture features characterize the magnitude, frequency content, and orientation of the trabecular bone pattern. Good correlation was found between the two modalities for the first moment (FMP) with r=0.71 (p value<0.0001) and for minimum FMP with r=0.52 (p value=0.008). Root-mean-square (RMS) did not correlate with r=0.31 (p value>0.05), while the standard deviation of the RMS did correlate with r=0.79 (p value<0.0001). Good correlation was also found between the two modalities for the fractal-based texture features with r=0.79 (p value<0.0001) for the global Minkowski dimension and r=0.63 (p value=0.0007) for the fractal dimension from a box counting method. The PD system therefore may have the potential for yielding heel images suitable for RTA.

Absorptiometry, Photon↗
PubMed1997

The CT's sample volume as an approximate, instrumental measure for density resolution in densitometry of the lung.

Ultimately CT-densitometry of the lung should give comparable results on all scanners. One prerequisite for this is the use of the same density resolution. Unfortunately, density resolution is impractical as a performance specifying parameter because it depends on the cellular material scanned. Therefore, another parameter that can be used for scanner and protocol characterization, and that does not depend on a special phantom, would be highly preferable. We investigated how well the CT's nominal sample volume (V), calculated from section thickness and in-plane spatial resolution as specified by the CT manufacturer, can serve as a simple measure, for density resolution. Six CT scanners were studied using foam and lung phantoms. On all scanners we observed for foam an approximately linear relation between density resolution and V-1/2. Density resolution on different scanners varied to some extent. These differences can be interpreted as being caused by deviations of the true sample volume from the nominal value: the 95%-confidence interval runs for instance for V = 8 mm3 from 4.6 mm3 to 16.9 mm3. Acceptability of this spread depends on the consequences for parameters of clinical interest, like percentiles and pixel indexes. To evaluate this we used data from a previous patient study on the dependence of histogram parameters on sample volume. With these data it is found that large interscanner differences in histogram parameters are possible for small values of V, as used in thin-section densitometry. For larger values of V, as required for a more adequate density resolution, the differences are much smaller and probably acceptable when compared to other sources of variability in lung densitometry. In conclusion, for sections of at least 2 mm and smooth reconstruction filters, corresponding to V > or = 8 mm3, the CT's nominal sample volume might be used for interscanner and interprotocol comparison of density resolution.

Absorptiometry, Photon↗