ORIGINAL RESEARCH

Diagnostic Performance of Vertebral Fracture Assessmentby the Lunar iDXA Scanner Compared to ConventionalRadiography

Daniele Diacinti • Romano Del Fiacco • Daniela Pisani • Federico Todde •

Maria Sofia Cattaruzza • Davide Diacinti • Serena Arima • Elisabetta Romagnoli •

Jessica Pepe • Cristiana Cipriani • Salvatore Minisola

Received: 18 May 2012 / Accepted: 31 July 2012 / Published online: 11 September 2012

� Springer Science+Business Media, LLC 2012

Abstract The purpose of this study was to evaluate the

diagnostic performance of vertebral fracture assessment

(VFA) using the Lunar iDXA scanner. Conventional spinal

radiographs and images acquired by dual-energy X-ray

absorptiometry (DXA) of 350 subjects (269 females, 81

males) were evaluated by two different readers. We visualized

4,476/4,550 (98.4 %) vertebrae from T4 to L4 on VFA images

compared to 4,535/4,550 (99.7 %) on radiographs. Among the

visualized vertebrae, 205/4,535 (4.5 %) and 190/4,476 (4.2 %)

were identified as nonfracture deformities by reading of

radiographs and VFA, respectively. Vertebral fractures (VFs)

were 231 in 126 patients and 228 in 125 patients by semi-

quantitative assessment of radiographs (SQ-Rx) and by VFA,

respectively. There was excellent agreement between the two

techniques and high diagnostic performance of VFA both on a

per-vertebra basis (k score = 0.984, 95 % CI 0.972–0.996,

sensitivity 98.68 %, specificity 99.91 %, PPV 98.25 %, NPV

99.93 %) and on a per-patient basis (k score = 0.957, 95 % CI

0.925–0.988, sensitivity 96.83 %, specificity 98.66 %, PPV

97.60 %, NPV 98.22 %). In older patients (C65 years) affected

by moderate or severe osteoarthritis, SQ-Rx and VFA iden-

tified 96 VFs and 95 versus 90 vertebral deformities, respec-

tively. This study demonstrates that most vertebrae are

evaluable using the iDXA scanner, with improved VFA

diagnostic performance even in discriminating mild VFs from

vertebral deformities. Therefore, VFA may be appropriate as

an alternative to conventional radiography in patients at high

risk of VF who are undergoing DXA bone densitometry and in

the follow-up of osteoporotic patients on treatment.

Keywords Dual-energy X-ray absorptiometry � Vertebral

fracture assessment � Vertebral fracture � Semiquantitative

assessment � Conventional radiography

Vertebral fractures (VFs) are the most common osteopo-

rosis-related fractures [1, 2], but many of these remain

unrecognized by clinicians and, therefore, undiagnosed

[3, 4] as they often are asymptomatic and occur in the

absence of specific trauma. The identification of VF has a

high predictive value, and it is important for the manage-

ment of osteoporotic patients because even with a mild

VF patients have approximately fivefold increased risk

of further VF and threefold increased risk of hip fracture

[5–7]. Multiple VFs are associated with an increased

mortality rate [8] and reduced quality of life [9].

The visual semiquantitative assessment of conventional

radiographs (SQ-Rx) described by Genant et al. [10] is one

of the most widely used methods to assess VF since it

achieves a high accuracy for diagnosing VF by an expert

The authors have stated that they have no conflict of interest.

D. Diacinti � D. Diacinti

Department of Radiology, Sapienza University of Rome,

Viale del Policlinico 155, 00161 Rome, RM, Italy

R. Del Fiacco � S. Arima � E. Romagnoli � J. Pepe �C. Cipriani � S. Minisola

Department of Clinical Sciences, Sapienza University of Rome,

Viale del Policlinico 155, 00161 Rome, RM, Italy

D. Pisani (&) � F. Todde

Department of Clinical and Molecular Medicine,

Sant’ Andrea Hospital, Sapienza University of Rome,

Via Grottarossa 1035-1039, 00189 Rome, RM, Italy

e-mail: pisdan@gmail.com

M. S. Cattaruzza

Department of Public Health and Infectious Diseases,

Sapienza University of Rome, P.le Aldo Moro5,

00185 Rome, RM, Italy

123

Calcif Tissue Int (2012) 91:335–342

DOI 10.1007/s00223-012-9643-0

reader, allowing one also to distinguish between true VFs

and vertebral deformities [11]. Because of the high radia-

tion effective dose (about 600 lSv), lateral radiographs of

the thoracic and lumbar spine are used only in patients with

back pain so that most VFs, which are asymptomatic, are

often undiagnosed in clinical practice [12].

In the last decade, new developments in dual-energy

X-ray absorptiometry (DXA) scanners (fan X-ray-beam

system with pile of detectors) have provided a means to

acquire lateral images of the thoracic–lumbar spine of good

quality to detect prevalent VF [13–15].

DXA offers several advantages over conventional radi-

ography, which include a significantly lower radiation

effective dose to the patient (from 2 to about 50 lSv) [16],

lack of distortion from parallax and magnification of the

image, and quick acquisition of a single image of the

thoracic and lumbar spine in the same session as bone

mineral density measurement, lowering costs [17].

The 2007 International Society of Clinical Densitometry

(ISCD) official positions [18] stated that vertebral fracture

assessment (VFA) is the correct term to denote densitometric

spine imaging performed for the purpose of detecting VFs.

Furthermore, recommendations were provided concerning

proper indications for VFA and appropriate methods for

defining and reporting fractures on VFA. The Genant visual

semiquantitative method was indicated as the current clinical

technique of choice for diagnosing VF with VFA. In spite of

this authoritative recommendation, VFA has not yet been

widely implemented in clinical practice because up to now

available DXA devices have had low spatial resolution

(1 mm per line pair) [19].

In comparative studies with conventional radiographs

for the detection of VFs, many vertebrae (10–15 %) could

not be visualized on lateral spine DXA images, mainly at

the upper thoracic level from T4 to T7, because of the poor

image quality of the available densitometers [20].

In fact, these studies demonstrated good specificity of

VFA varying from 94 to 99 % but low sensitivity ranging

from 62 to 85 %. The variability of these results arose both

from the model of densitometers used, Hologic 4500A or

Delphi C (Hologic, Bedford, MA) [21–23] and Lunar

EXPERT-XL [24] and Lunar Prodigy [25–27] (GE Medical

Systems Lunar, Madison, WI), and from characteristics of

the studied populations.

GE Healthcare has recently developed the Lunar intel-

ligent DXA (iDXA), a fan-beam densitometer that uses

slightly higher amounts of radiation and enhanced detector

capabilities, the latter yielding improved spatial resolution

up to 0.3 mm per line pair [28].

The purpose of this study was to evaluate the reliability

and diagnostic performance of VFA in the identification of

VFs using the iDXA scanner in comparison with conven-

tional radiography.

Methods

Subjects

We enrolled 350 patients (269 females and 81 males; mean age

± SD 60.6 ± 11.6 years, range 28–85) consecutively referred to

our Mineral Metabolism Centre. They were recruited from two

sources: peri- and postmenopausal women and men referred by

general practitioner for diagnosis of osteoporosis and patients

from a study of HIV-related osteoporosis.

All patients gave written, informed consent. The study

was approved by the local ethics committee. No patients

were excluded for any health reasons (including previously

diagnosed VFs).

VFA

Lateral images of the thoracic–lumbar spine were acquired

using a Lunar-iDXA densitometer (GE Medical Systems

Lunar). This device uses a stable X-ray source with a current

of 2.5 mA and a peak X-ray energy of 100 kVp that is filtered

by a K-edge filter at 46 keV for low energy and 81 keV for

high energy. The Lunar-iDXA uses a narrow-angle (4.5�) fan

beam oriented orthogonal to the long axis of the body. The

limited-angle fan beam avoids image distortion in the

transverse direction observed with wide-fan beam devices.

The iDXA system uses a staggered array of 64 direct-digital

high-definition cadmium zinc telluride detectors—51 9

5 mm wide—to eliminate dead space between detectors

creating a high-resolution image. The enhanced digital

detectors increase image resolution, especially for bone.

Spatial resolution, evaluated by iDXA scan of a 10 line pair

phantom, was 3 LP/mm.

The patient was positioned in the left lateral decubitus,

according to the manufacturer’s guidelines. The position was

similar to standard spinal radiographs with the knees and hips

flexed in a 90� angle and the arms flexed with both hands

joined, so that the spine was parallel to the table to avoid

tilting of the vertebrae. Lateral spine VFA images, by dual-

energy modality, were used for fracture assessment, given

that the upper thoracic vertebrae are more clearly seen on

dual-energy than on single-energy images. Assuming that

the scan started in the sacrum and ended near T4, the scan

time (with Smart Scan) was estimated to be 120–240 s,

depending on patient size.

The effective radiation dose for a DXA lateral spine

scan set on standard thickness using iDXA was *12 lSv,

as declared by the manufacturer.

On spine VFA images the enCORETM Software v13.5

(Encore Software, San Jose, CA) automatically performed

vertebral morphometry, placing six points in each vertebral

body from L4 to T8 to calculate the anterior (Ha), middle (Hm),

and posterior (Hp) heights and their ratios (Ha/Hp, Hm/Hp) as

336 D. Diacinti et al.: Diagnostic Performance of VFA

123

well as the average height (HAVG) of each vertebra. The

software automatically estimated the extent of anterior or

middle vertebral height reduction with respect to posterior

height, classified the vertebrae as normal (\20 % reduction) or

fractured (wedge, biconcave, or crush), grading as mild

(20–25 % reduction), moderate (25–40 % reduction), or

severe ([40 % reduction) fractures according to the criteria of

Genant et al. [10].

Each automatic vertebral morphometry was reviewed by

a physician (R.D.F.) specialist in bone diseases with 5

years of VFA experience, who corrected manually the

marker placement in *30 % of the patients, according to

Hurxthal criteria [29]. He measured manually also the

heights of vertebrae from T7 to T4 if they were adequately

visualized.

The same physician interpreted the report of vertebral

morphometry considering both vertebral shape and the

appearance of the end plate in order to differentiate VFs

from other causes of vertebral deformities (e.g., develop-

mental variant, degenerative change, large Schmorl nodes,

Scheuermann disease) according to the ABQ method [30].

The time needed to perform VFA with vertebral mor-

phometry, including the operator review, averaged 6.5 ±

1.5 min (range 3.5–10.2).

To assess the intraoperator reproducibility of vertebral

morphometry, the spine DXA images of 50 subjects ran-

domly selected from the study population were analyzed by

the same operator twice with an interval of more than 30

days, blinded to the previous analysis.

Spine Radiographs

Conventional radiographs of the thoracic and lumbar spine

in anteroposterior and left lateral projections were acquired

by using a full digital radiographic system (Apollo DRF;

Villa Medical Systems, Milan, Italy) with the patients

positioned on the left side with the knees and hips flexed.

Tube-to-film distance was set at 105 cm, and the X-ray

beam was centered at T7 and L3 for the thoracic and

lumbar views, respectively. Conventional radiographs were

examined for VF identification by an experienced skeletal

radiologist (D.D.), who used ABQ in order to discriminate

nonfracture vertebral deformities and then classified the

true VFs according to visual SQ-Rx [10].

Statistical Analysis

Intraoperator precision was reported as the root mean

square standard deviation (RMS SD) and the coefficient of

variation (CV) of the differences between vertebral heights.

We calculated the frequency of unreadable vertebrae by

vertebral level and the prevalence of fracture, per person

and per vertebra, classifying VFs according to grade

(normal, mild, moderate, and severe).

The overall agreement, beyond that expected by chance

alone, between VFA and SQ-Rx was evaluated using a

simple kappa statistic and associated 95 % confidence

intervals (CIs). To assess the diagnostic value of VFA we

also calculated sensitivity, specificity, and positive and

negative predictive values (PPVs, NPVs) considering SQ-

Rx as the gold standard. In computing all these parameters,

vertebrae that were unreadable were classified as normal.

Finally, we repeated calculations including only subjects

with age C65 years. Analyses were performed using

statistical software (SPSS, version 18; SPSS, Inc.,

Chicago, IL).

Results

Intraoperator precision for vertebral morphometry resulted

in CV and RMS SD as follows: 1.4 % and 0.28 mm for Ha,

1.5 % and 0.27 mm for Hm, 1.7 % and 0.35 mm for Hp, 1.9

% and 0.37 mm for average height, 2.0 % and 0.019 for Ha/

Hp ratio, and 2.6 % and 0.023 for Hm/Hp ratio.

Per-vertebra Analysis

Of a total of 4,550 vertebrae from T4 to L4, the visualized

vertebrae were 4,535 (99.7 %) in the conventional radio-

graphs and 4,476 (98.37 %) in the VFA images. All unana-

lyzable vertebrae in the standard radiographs (n = 15) and in

the VFA images (n = 74) were localized in the upper thoracic

spine (T4–T6), most of them at T4 level (13 in standard

radiographs and 57 in VFA images).

Among the visualized vertebrae, 205/4,535 (4.5 %)

and 190/4,476 (4.2 %) were identified as nonfracture

vertebral deformities applying the ABQ approach to the

radiographs and VFA images, respectively. In detail,

vertebral deformities identified by conventional radiogra-

phy and by VFA were, respectively, 151 versus 144

degenerative changes, 2 versus 2 Scheuermann disease, 7

versus 7 developmental variations, and 45 versus 37

Schmorl nodes (Fig. 1).

There were 231 vertebrae classified as fractured by

SQ-Rx, whereas VFA detected 228 fractures (Fig. 2). Table

1 shows the number and grading of VFs assessed by the

two different techniques.

There was excellent agreement for VF identification,

assessed by k statistics, between SQ-Rx and VFA (agree-

ment 99.76 %, k score = 0.975, 95 % CI 0.960–0.990).

When considering also the grading of vertebral deformity,

the agreement was also very good (agreement 98.5 %,

k score = 0.871, 95 % CI 0.841–0.901).

D. Diacinti et al.: Diagnostic Performance of VFA 337

123

Fig. 1 Nonfracture vertebral deformities identified by vertebral frac-

ture assessment images. a Scheuermann disease: vertebrae T6–T11 are

wedge-shaped (T7 and T8 with height reduction [20 %) with undu-

lated end plates, multiple Schmorl nodes, and disc space narrowing.

Anterior osteophytes are also present at vertebrae T8–T10. b Large

Schmorl node at the inferior end plate of vertebra T12 producing a

monoconcave appearance. c Degenerative changes: osteoarthritis with

remodeling at vertebrae T6–T9 into wedge shape. Hemangioma of

vertebra L2

Fig. 2 Moderate fracture of T5

with anterior height

reduction [25 % (wedging) and

mild fracture of L2 with middle

height reduction [20 %

(concavity) as identified by

vertebral fracture assessment

(a) and conventional

radiography (b)

338 D. Diacinti et al.: Diagnostic Performance of VFA

123

Accepting SQ-Rx as the gold standard, all diagnostic

performance parameters of VFA were very high (sensitivity

98.68 %, specificity 99.91 %, PPV 98.25 %, NPV 99.93 %)

(see Table 2).

In Fig. 3 the distribution of VFs assessed by the two tech-

niques is reported for each level. Most VFs were localized at

T7–T8 and T11–L1 levels. Among the 74 unreadable verte-

brae by VFA, four were classified as mild VFs by reading of

radiographs.

Per-patient Analysis

Of the patients, 126 (36.0 %) and 125 (35.7 %) were judged

to have at least one VF by SQ-Rx and VFA, respectively.

Also, 46/126 and 45/125 had multiple VFs. On a per-patient

basis, the agreement of the two techniques was still excellent

(k score = 0.957, 95 % CI 0.925–0.988).

There were very slight changes in performance diagnostic

parameters (sensitivity 96.83 %, specificity 98.66 %, PPV

97.60 %, NPV 98.22 %) (see Table 2).

Patients Aged C65 Years

Concerning patients aged 65 years or older (n = 142, F =

122, M = 20), most were affected by moderate or severe

overall spinal osteoarthritis, according to radiographic scale

[31]. In this elderly subgroup, both SQ-Rx and VFA iden-

tified 96 VFs, whereas the two techniques slightly disagreed

in the identification of vertebral deformities (95 by SQ-Rx

and and 90 by VFA). The statistical analysis of same

Table 1 Vertebral fractures and vertebral deformities assessed by SQ-Rx and VFA

Normal Any fracture Mild fracture Moderate fracture Severe fracture Not analyzed Vertebral deformities Total

SQ-Rx 4,304 231 148 61 22 15 205 4,550

VFA 4,248 228 143 63 22 74 190 4,550

Table 2 Diagnostic agreement of VFA with the standard SQ-Rx method on a per-patient or a per-vertebra basis

Per-vertebra Per-patient Per-vertebra C65 years Per-patient C65 years

Agreement (%) 99.76 98.0 99.82 99.3

k Score 0.975 0.957 0.988 0.986

95 % CI 0.960–0.990 0.925–0.988 0.974–1.002 0.938–1.014

Sensitivity (%) 96.97 96.83 99.25 100

Specificity (%) 99.91 98.66 99.87 98.46

PPV (%) 98.25 97.60 98.51 98.72

NPV (%) 99.84 98.22 99.94 100

Fig. 3 Vertebral fractures per

vertebral level by

semiquantitative (SQ)

assessment of radiographs and

vertebral fracture assessment

(VFA) on DXA images

D. Diacinti et al.: Diagnostic Performance of VFA 339

123

parameters failed to demonstrate important changes with

respect to the whole population enrolled (see Table 2).

Discussion

This study demonstrated in a large sample of patients that

the improved quality of images by the new iDXA densi-

tometer leads to a higher accuracy of VFA in the diagnosis

of VF, identifying also most mild VFs.

In fact, most vertebrae (98.4 %) were adequately visu-

alized in VFA images. The clinical impact of the 74

unreadable vertebrae by VFA was minimal because most

of them (n = 57) were localized at the T4 level, where

fracture rarely occurs. Therefore, only four unreadable

vertebrae by VFA were classified as mild fractures by

SQ-Rx, and three of them were in patients with other VFs

who were correctly identified as ‘‘patients with fractures.’’

Furthermore, as previously reported [32], most VFs

were localized at T7–T8 and T11–L2 vertebral levels,

where all vertebrae were always well visualized. A simi-

larly high percentage of readable vertebrae was reported in

some recently published studies. Buehring et al. [33]

demonstrated that iDXA adequately visualized from T6

through L4 95 % of vertebrae compared to 87 % of ver-

tebrae by Prodigy. In two other studies, lateral spine DXA

scans were acquired using the Hologic Discovery-A

device, a densitometer with the scanner arm rotated 90�and with the patient in the supine position throughout the

procedure. Hospers et al. [34] reported in 250 patients that

98.7 % of vertebrae from L4 through T4 were analyzable

for VFA. Jager et al. [35], performing a study on a larger

population with the same densitometer, the Hologic

Discovery-A, found that the percentage of readable verte-

brae was high (93 %) in 2,247 patients from L4 through T5

but decreased to 82 % when T4 was included in the eval-

uation. The ability to adequately visualize most vertebrae

included in the scan region using the new densitometers

owing to higher resolution of images improved the diag-

nostic performance of VFA to detect vertebral fractures

[36].

In fact, the results of our study show that VFA by iDXA

had very high sensitivity and specificity and excellent

agreement with SQ-Rx, misclassifying only 11 among

4,550 vertebrae.

The accuracy of VFA performed by older models of

densitometers was lower, with sensitivity up to 84 % in

detecting vertebral fractures [21–25, 37, 38]. In all these

comparative studies, VFA was less accurate in detecting

mild VFs with respect to moderate and severe fractures. In

our study, only three mild VFs identified by SQ-Rx were

undiagnosed by VFA. It has been emphasized that the

clinical significance and true nature of mild vertebral

deformities, defined as 20–25 % height reduction, are often

questionable because vertebral deformities are not always

due to osteoporotic VFs [23, 39, 40]. Although it may be

difficult especially in mild deformities, it is necessary to

discriminate between true VF and nonfracture vertebral

deformities, in particular the so-called short vertebral

height (SVH) deformity [41]. The presence of SVH is the

greatest source of misclassification of VF, particularly by

quantitative vertebral morphometry that always judges

mild vertebral deformities as VFs.

Current guidelines for VFA [18] recommend use of the

SQ method for visual estimation of apparent reduction in

vertebral height C20 % for diagnosis of a prevalent VF.

This approach may be problematic because of the presence

of nonosteoporotic deformities that may also appear as

wedging or concavities for vertebral height reduction. The

ABQ method instead focuses on the appearance of the

central vertebral end plates to identify prevalent fractures

rather than on the appearance of ‘‘reduced’’ (short) verte-

bral height [30]. Recently, the ABQ method has been

applied in VFA, resulting in very high specificity with

absence of false-positive VFs caused by misclassification

of nonfracture deformities. Nevertheless, sensitivity was

low as the poor image quality of older DXA densitometers

led to a high percentage of false-negatives: 41 % of

radiographic VFs were either missed by VFA or not ana-

lyzed [42].

In our study we demonstrated that the high quality of

images by iDXA allowed most vertebrae to be visualized

adequately, improving the sensitivity of VFA to identify,

according to the criteria of Genant et al. [10], most VFs,

even mild, differentiating them from several other causes

of vertebral deformities. In fact, using the ABQ method,

VFA missed only 15 nonfracture vertebral deformities with

respect to conventional radiographs, demonstrating high

accuracy in the assessment of VF status.

Hence, when performing VFA, nonosteoporotic defor-

mities should be ruled out first, performing an accurate visual

assessment of all vertebrae by an expert reader using the

ABQ method, followed by determination of fracture severity

either with the SQ approach or with vertebral quantitative

morphometry. Furthermore, it could be necessary to com-

pare the measured vertebral dimensions with reference ver-

tebral height values specific for the population and probably

even for age groups to identify VFs with better accuracy for

both epidemiological studies and clinical practice [43].

Moreover, VFA images allowed us to visualize osteophytes

and vertebral remodeling due to osteoarthritis as well as

conventional radiography. In fact, our results demonstrated

that in a subgroup of older patients[65 years the presence of

moderate to severe osteoarthritis did not interfere with the

diagnostic performance of VFA, which identified in these

patients the same number of VFs as SQ-Rx.

340 D. Diacinti et al.: Diagnostic Performance of VFA

123

This study had some limitations. The studied population

included a sample (26.8 %) of relatively young patients

(mean age 50.4 ± 10.2) with suspected HIV-related oste-

oporosis. Most of these patients had absent or mild osteo-

arthritis, allowing good visibility of most vertebrae to be

analyzed by VFA. This could explain the high specificity of

VFA in our study. However, no important difference

resulted in the statistical analysis restricted to patients aged

C65 years. Furthermore, the conventional radiography that

we used as a reference standard has some well-known

limitations due to the X-ray cone beam, which causes

geometric distortion of vertebrae located at the extremities

of the scans Therefore, some vertebrae at T4–T5 level,

identified by SQ-Rx as mild fractures and judged as normal

vertebrae on VFA, could be false VFs as a result of error

from parallax of conventional radiography.

The important result obtained in this study is the

excellent agreement between the two methods, SQ-Rx and

VFA, first due to the integration of advanced iDXA tech-

nology with the experience of both readers. Second, patient

position in lateral decubitus was the same in the acquisition

of both iDXA scans and standard spinal radiographs. Third,

both examinations were performed on the same day, by a

single technician for each method, using the same X-ray

device and the same densitometer. Thus, errors due to the

use of different devices and technicians were eliminated,

improving the validity of our comparison of the two

techniques.

Appropriate indications for using VFA, in both women

and men, were suggested by the ISCD official positions, to

detect VFs among patients at high risk of fracture [18],

even though for mild fractures VFA by older DXA scan-

ners had lower sensitivity than conventional radiography. It

should be emphasized that even if mild VFs are often

asymptomatic, they significantly increase the risk of new

VFs in osteoporotic patients.

Considering the high performance of new DXA scanners

in identifying even mild VFs, we suggest the introduction of

VFA as an alternative to conventional radiography in

patients at high risk of VF who are undergoing DXA bone

densitometry and in the follow-up of osteoporotic patients on

treatment. However, it should be recommended to integrate

the advanced DXA technology with operator formal training

in, and subsequent experience with, VFA interpretation to

achieve high accuracy in VF identification.

In conclusion, VFA is a reliable and practical tool for

diagnosing VFs, taking into account its low radiation

effective dose and the opportunity of combined assessment

of bone mineral density and vertebral fracture status.

Conflict of interest The authors have stated that they have no

conflict of interest.

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