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Abstract: Evaluation of vertebral fracture assessment images for the detection of abdominal aortic calcification



Dual-energy x-ray absorptiometry (DXA) is an established modality for the assessment of bone mineral density. DXA has also been used for the detection of abdominal aortic calcification (AAC) using lateral images taken for vertebral fracture assessment (VFA). In this phantom study, the capability of VFA for the detection of AAC was investigated. A Perspex phantom of variable width in the range 15-30 cm was used to simulate abdominal soft tissue. Aluminium strips of thickness 0.05-2.0 mm were sandwiched between two halves of the phantom to mimic aortic calcification. VFA images of the phantom were acquired in single-energy mode and analysed by placing regions of interest over the aluminium strip and an adjacent area of Perspex. For each phantom width, the minimum detectable aluminium thickness was assessed visually and related to contrast-to-noise ratio (CNR). Linearity of pixel value with aluminium thickness was tested by linear regression and correlation. Repeatability was measured with five repeated scans for selected phantom configurations. The minimum thickness of aluminium that could be visualised increased with phantom width and varied from 0.05 mm at 15 cm Perspex to 0.5 mm at 30 cm Perspex; the CNR threshold was about 0.03. At all phantom widths, the variation of pixel value with aluminium thickness was strongly linear (r²>0.98, p<0.001). Repeatability was good with a coefficient of variation of less than 0.04%. The results of the study suggest that under idealised imaging conditions, VFA is capable of detecting small thicknesses of calcification with good linearity and repeatability.
Evaluation of vertebral fracture assessment images for the detection of
abdominal aortic calcification
Elmasri K1, Hicks Y1, Yang X1 , Sun X2, Pettit RJ3, Evans WD1,3
1School of Engineering and 2School of Computer Science and Informatics, Cardiff University, Queen’s Buildings, Cardiff CF24 3AA
3Medical Physics and Clinical Engineering, Cardiff and Vale University Health Board, University Hospital of Wales, Cardiff CF14 4XW
Fig 1 Phantom in position on DXA scanner couch for VFA scan
Perspex and
𝑪𝑵𝑹 =(𝑵𝑨𝒍 − 𝑵𝑷)
𝑵𝒐𝒊𝒔𝒆 = 𝝈𝑷
Abdominal aortic calcification (AAC) is a marker of
cardiovascular disease
The chemical composition of AAC is identical to calcium
hydroxyapatite (bone mineral)
Dual-energy x-ray absorptiometry (DXA) is an established
modality for the assessment of bone mineral density in
relation to conditions such as osteoporosis
AAC may be detected with a DXA scanner using lateral
images taken for vertebral fracture assessment (VFA)
The capability of VFA to detect AAC was investigated
with a phantom designed and constructed for this purpose
A Perspex (P) phantom of 15-30 cm variable width was
used to simulate soft tissue and aluminium (Al) strips of
thickness 0.05-2.0 mm were sandwiched between two
halves of the phantom to mimic AAC
VFA images of the phantom acquired in single-energy
mode with a Hologic Horizon DXA scanner (Fig 1)
Mean (N) and standard deviation (σ) of pixel values were
obtained for regions of interest (ROIs) in P and Al and
used to calculate contrast (C), noise and contrast to noise
ratio (CNR) (Fig 2)
Minimum detectable aluminium thickness was assessed
visually for all P-Al combinations and related to CNR
Variation of C and CNR with Al thickness was explored
for different values of P width
Repeatability of C and CNR was measured with 5
repeated scans for selected phantom configurations and
expressed as the coefficient of variation (%)
Materials and Methods
Minimum detectable Al thickness increased with phantom width
and varied from 0.05 mm at 15 cm Pto 0.3 mm at 30 cm P
CNR threshold for detection of the Al strip was in the range
0.04 to 0.10
Linear regression and correlation revealed good linearity of
contrast with Al thickness for all P widths (Fig 3)
Noise increased with P width and CNR increased with Al
thickness for a given P width (Fig 3)
At a P width of 25 cm, the repeatability of C and CNR varied
from about 20% for 0.1 mm Al thickness to about 1% for 2 mm
Al thickness
The results of the study suggest that under idealised imaging
conditions, VFA is capable of detecting small thicknesses of
calcification with acceptable linearity and repeatability.
𝑪𝒐𝒏𝒕𝒓𝒂𝒔𝒕 = 𝑵𝑨𝒍 − 𝑵𝑷
Fig 2 VFA image of phantom with
ROIs (left) and definitions of contrast,
noise and CNR (above)
Fig 3 Variation of contrast (left) and CNR (right) with
aluminium thickness for different Perspex widths
a) y = 0.0099x + 0.0006
R² = 0.999, p<0.001
b) y = 0.0092x + 0.0003
R² = 0.998, p<0.001
c) y = 0.0085x + 0.0002
R² = 0.997, p<0.001
d) y = 0.0082x + 0.0003
R² = 0.986, p<0.001
0 0.5 1 1.5 2
Aluminium thickness in mm
a) 15 cm
b) 20 cm
c) 25 cm
d) 30 cm
00.2 0.4 0.6 0.8 11.2 1.4 1.6 1.8 2
Aluminium thickness in mm
15 cm
20 cm
25 cm
30 cm
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20th INTERNATIONAL CONFERENCE ON KNOWLEDGE-BASED AND INTELLIGENT INFORMATION AND ENGINEERING SYSTEMS, 5-7 SEPTEMBER 2016 (KES 2016), YORK, ENGLAND, UK. Cardiovascular disease (CVD) is a major cause of mortality and the main cause of morbidity worldwide. CVD may lead to heart attacks and strokes and most of these are caused by atherosclerosis; this is a medical condition in which the arteries become narrowed and hardened due to an excessive build-up of plaque on the inner artery wall. Arterial calcification and, in particular, abdominal aortic calcification (AAC) is a manifestation of atherosclerosis and a prognostic indicator of CVD. In this paper, a two-stage automatic method to detect and quantify the severity of AAC is described; it is based on the analysis of lateral vertebral fracture assessment (VFA) images. These images were obtained on a dual energy x-ray absorptiometry (DXA) scanner used in single energy mode. First, an active appearance model was used to segment the lumbar vertebrae L1-L4 and the aorta on VFA images; the segmentation of the aorta was based on its position with respect to the vertebrae. In the second stage, feature vectors representing calcified regions in the aorta were extracted to quantify the severity of AAC. The presence and severity of AAC was also determined using an established visual scoring system (AC24). The abdominal aorta was divided into four parts immediately anterior to each vertebra, and the severity of calcification in the anterior and posterior walls was graded separately for each part on a 0-3 scale. The results were summed to give a composite severity score ranging from 0 to 24. This severity score was classified as follows: mild AAC (score 0-4), moderate AAC (score 5-12) and severe AAC (score 12-24). Two classification algorithms (k-nearest neighbour and support vector machine) were trained and tested to assign the automatically extracted feature vectors into the three classes. There was good agreement between the automatic and visual AC24 methods and the accuracy of the automated technique relative to visual classification indicated that it is capable of identifying and quantifying AAC over a range of severity.
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Coronary atherosclerosis is frequently associated with calcification of arterial plaque. To understand the mechanisms responsible for the formation of atherosclerotic calcification, we examined human coronary arteries for the presence and extent of mineral. In sections stained specifically for mineral, staining was diffuse and present in all atherosclerotic plaques. Hydroxyapatite was not detected in normal coronary artery sections. Distribution of hydroxyapatite coincided with a similar distribution of calcium detected by a radiodense pattern using contact microradiography of the same sections before cytochemical staining. By energy-dispersive x-ray microanalysis, the chemical composition of calcified sites was identical to hydroxyapatite (Ca10[PO4]6[OH]2), the major inorganic component of bone. Osteopontin is a phosphorylated glycoprotein with known involvement in the formation and calcification of bone and is regulated by local cytokines. Human coronary artery segments (14 normal and 34 atherosclerotic) obtained at autopsy were evaluated immunohistochemically using polyclonal antibodies generated against human osteopontin. Immunohistochemistry for osteopontin indicated intense, highly specific staining in the outer margins of all diseased segments at each calcification front; staining was evident throughout the entire plaque. Conversely, arterial segments free of atheroma and calcification and sections treated with nonimmune serum had no evidence of positive staining. Osteopontin, a protein involved in mineralization is specifically associated with calcific coronary atheroma and may play an important role in the onset and progression of this disease in human coronary arteries. The deposition of noncollagenous proteins such as osteopontin may regulate the presence or absence of calcification and ultimately alter vessel compliance.
Full-text available
Dual-energy X-ray absorptiometry (DXA) is recognized as the reference method to measure bone mineral density (BMD) with acceptable accuracy errors and good precision and reproducibility. The World Health Organization (WHO) has established DXA as the best densitometric technique for assessing BMD in postmenopausal women and based the definitions of osteopenia and osteoporosis on its results. DXA allows accurate diagnosis of osteoporosis, estimation of fracture risk and monitoring of patients undergoing treatment. However, when DXA studies are performed incorrectly, it can lead to major mistakes in diagnosis and therapy. This article reviews the fundamentals of positioning, scan analysis and interpretation of DXA in clinical practice.
Aluminium is often used as a substitute material for calcifications in phantom measurements in mammography. Additionally, calcium oxalate, hydroxyapatite and aluminium are used in simulation studies. This assumes that these materials have similar attenuation properties to calcification, and this assumption is examined in this work. Sliced mastectomy samples containing calcification were imaged at ×5 magnification using a digital specimen cabinet. Images of the individual calcifications were extracted, and the diameter and contrast of each calculated. The thicknesses of aluminium required to achieve the same contrast as each calcification when imaged under the same conditions were calculated using measurements of the contrast of aluminium foils. As hydroxyapatite and calcium oxalate are also used to simulate calcifications, the equivalent aluminium thicknesses of these materials were also calculated using tabulated attenuation coefficients. On average the equivalent aluminium thickness was 0.85 times the calcification diameter. For calcium oxalate and hydroxyapatite, the equivalent aluminium thicknesses were 1.01 and 2.19 times the thickness of these materials respectively. Aluminium and calcium oxalate are suitable substitute materials for calcifications. Hydroxyapatite is much more attenuating than the calcifications and aluminium. Using solid hydroxyapatite as a substitute for calcification of the same size would lead to excessive contrast in the mammographic image.