A phantom for evaluating bone mineral density of the hand by dual-energy x-ray absorptiometry

Dual-Energy X-Ray Absorptiometry for Measurement of Phalangeal Bone Mineral Density on a Slot-Scanning Digital Radiography System

OBJECTIVE

In this paper, we assess the feasibility of using two detectors in a slot-scanning digital radiography system to acquire images for measuring bone mineral density (BMD) of the middle phalanx of the middle finger using dual-energy X-ray absorptiometry (DXA).

METHODS

Simulations were used to evaluate the spectral separation of the low- and high-energy spectra and detective quantum efficiency was used for assessing image quality. Scan parameters were chosen to optimize spectral separation, image quality, and radiation dose. We introduce the measurement of volumetric BMD (vBMD) using basis material decomposition. We assess the accuracy of our methods by comparing measurements taken using bone images against reference data derived from subsequent incineration of the bones. In vivo scans were conducted to evaluate the system precision (repeatability) and agreement with a clinical densitometer.

RESULTS

Average errors for bone mineral content (BMC), areal BMD (aBMD), and vBMD were 4.85%, 5.49%, and 12.77%, respectively. Our system had good agreement with a clinical densitometer based on concordance correlation coefficient values of 0.92 and 0.98 for aBMD and BMC, respectively. Precision studies yielded coefficient of variation (CV) values of 1.35% for aBMD, 1.48% for BMC, and 1.80% for vBMD. The CV values of all measurements were within 2%, indicating that the methods have clinically acceptable precision.

CONCLUSION

We conclude that our techniques yield bone measurements with high accuracy, clinically acceptable precision, and good agreement with a clinical densitometer.

SIGNIFICANCE

We have shown the clinical potential of phalangeal DXA measurements of aBMD and vBMD on a slot-scanning digital radiography system.

Computed digital absorptiometry for measurement of phalangeal bone mineral mass on a slot-scanning digital radiography system

Computed digital absorptiometry is a low-cost and low-radiation technique for rapid measurement of phalangeal bone mineral mass. We implement and evaluate this technique on a slot-scanning radiography system. Results, based on measurements of excised phalangeal bones, indicate that the technique has potential for use in clinical assessment of osteoporosis.

INTRODUCTION

The current gold standard method for bone assessment in the diagnosis of osteoporosis requires specialised and expensive machines, highly trained personnel to conduct the examination and is available only at specialist centres. The technique, termed dual-energy X-ray absorptiometry (DXA), involves taking a bone mineral density measurement at the femur or lumbar spine. Measurements of bone at peripheral sites such as the phalanges using DXA and other techniques have been shown to have potential use in the diagnosis of osteoporosis. Computed digital absorptiometry (CDA) is a low-cost, low-radiation radiographic technique for assessing phalangeal bone mineral mass. It uses an aluminium step wedge as a calibration device to compute bone mineral mass in units of equivalent aluminium thickness. In this study, we assess the feasibility of using CDA on a slot-scanning radiography system for measuring phalangeal bone mineral mass.

METHODS

We implement and evaluate fully automated computed digital absorptiometry (CDA) of the middle phalanx of the middle finger on a slot-scanning radiography system.

RESULTS

The ash weight of incinerated bones was measured and shown to have a correlation of 0.92 with CDA-derived bone mineral mass. CDA measurements had a coefficient of variation of 0.26%, indicating high precision.

CONCLUSION

We conclude, based on these results, that CDA on a slot-scanning radiography machine may be useful for clinical assessment of osteoporosis.

Imaging of small high-density structures in CT A phantom study

RATIONALE AND OBJECTIVES

The aim of this work is to study how the limited spatial resolution of a computed tomographic (CT) system affects the imaging of small high-density structures. This knowledge is relevant not only to understand and interpret clinical data, but also to apply and develop quantification methods for calcifications and stented vessels.

MATERIALS AND METHODS

A dedicated phantom containing small differently sized aluminum cylinders was imaged on a 64-slice multidetector row CT (MDCT) while varying acquisition and reconstruction parameters from a high-resolution protocol. In addition, a bead phantom was imaged to estimate the point spread function (PSF) for the different parameter settings. The accuracy in determining object density and size was established for various imaging protocols and compared with simulations based on the estimated PSF.

RESULTS

Attenuation values and size measurements were accurate for objects larger than two times the size of the system PSF at the full-width-at-half-maximum. For smaller objects, attenuation values were increasingly underestimated and size was increasingly overestimated. The convolution kernel had the most influence on object signal and size. Use of edge-enhancing kernels yielded more accurate size measurements and higher signal for small objects. However, their application was constrained by noise amplification and edge-ringing artifacts, which led to lower signal-to-noise ratio, degrading the visualization of low densities and small high-density objects.

CONCLUSION

Results presented in this report provide insight into limitations in the quantification of small high-density structures and their effect on the visualization of surrounding tissues with recently developed MDCT systems.

Bone mineral measurement of phalanges: comparison of radiographic absorptiometry and area dual X-ray absorptiometry

With a standard, image-intensifier-based, digital radiographic system, high-spatial-resolution images of the hand were acquired for analysis of phalangeal bone mineral density with dual x-ray absorptiometry (DXA). Results with phalangeal DXA had precision of plus or minus 0.67% and accuracy of 4.1% and correlated well with those with radiographic absorptiometry. This phalangeal DXA technique is potentially useful for clinical diagnosis of osteoporosis.