Achilles Technical Info


	Lunar Achilles Express


	SPECIFICATIONS Precision in vivo 2.OO/o CV in osteoporotic patients Patient Throughput 1-minute measurement Signal Analysis Real-time, Fourier transform analysis with bi-directional measurement and convergence algorithms Ultrasonometry Transducers Fluid-coupled, through-transmission Quarter wave-matched, broadband single element (25 mm diameter) Center frequency 500 KHz Results STIFFNESS Index T-score and % Young Adult Z-score and % Age-Matched


	Display LCD "touch" screen Swivels to multiple positions Printer Thermal printer Batch printing Results can be attached to preprinted report form Fluid Coupling System Fully automated and self-contained Heated to 330 C (92'F) Replaceable silicon membranes Water-soluble ultrasonic gel Electrical Requirements 95-2 40 volts, 50/60 Hz @ 4A Physical Factors Integrated transportable design Dimensions (WxHxD): 25x31x61cm (10x12x24 in) Operating range temperature: 15-35C / 59-95F Humidity: 20~80% Weight: 10kg (22 Ibs)


	Accuracy If there was ever a doubt about the effectiveness of quality low cost ultrasonometers like the Achilles Express vs. expensive DEXA equipment, just check out the test results and read the facts about how Achilles STIFFNESS INDEX nearly matches DEXA.

Ultrasonometry: Only Achilles Provides Valid WHO T-Scores

Ultrasonometry has now come of age [1]. There are over 5000 ultrasonometers in the world of which 4000 (80%) are used for measurement of trabecular bone of the os calcis. The remaining 1000 units are used to measure speed of sound (SOS) at the surface of compact bone in the tibia, finger, and forearm. The diagnostic sensitivity of those latter devices is extremely poor [2,3], a deficiency which is due only in part to their poor precision. Rather, SOS measurements on compact bone show the same poor diagnostic sensitivity associated with finger and forearm BMD. Blanckaert et al [3] recently reported a detailed comparison of phalangeal SOS, axial BMD, and Stiffness on the heel. The latter two measurements were twice as sensitive as phalangeal SOS (Table 1). Mallmin et al [2] found a similar lack of sensitivity for phalangeal SOS in relation to hip fracture. The Z-score for finger SOS is usually normal in fracture patients, averaging 0.7 to 1 .0 SD higher than that for axial BMD or Stiffness.

Table 1. Z-scores comparing osteoporotic patients, or corticosteroid-treated patients, and age-matched controls; from Blanckaert et al [3, 12]

Osteoporotic Steroid
Phalangeal SOS -0.4 -
Spine BMD -0.9 -0.6
Femur BMD -1.1 -0.6
Os Calcis BUA -1.0 -0.7
Os Calcis SOS -0.9 -0.8
Os Calcis Stiffness -1.1 -0.8

New studies are showing that ultrasound measurements on the heel predict failure loads of both the proximal femur and vertebra, although not with the exactitude of direct DEXA measurement [4,5]. In contrast, SOS on compact bone is not related to failure load at axial sites. The ability to measure the trabecular bone of the os calcis directly, with little interference from overlying soft-tissue, and no contribution from the compact bone, may be one reason for the better diagnostic sensitivity of heel ultrasonometry. BUA, SOS, and Stiffness of the os calcis correlate highly (--0.85) with BMD of the purely trabecular bone [6,7]. BUA largely reflects BMD rather than structure, but SOS reflects trabecular connectivity [8,9]. This may be one reason that Stiffness, which includes a contribution from SOS, gives better sensitivity.

All ultrasonometers that measure the heel have good diagnostic sensitivity, although only a few comparisons have been done [10-14]. The Z-score comparing osteoporotics to age-matched controls is about -1 using Stiffness with Achilles. Other ultrasonometers produce Z-scores from -0.5 to -0.8. In part, the better sensitivity of the Achilles is due to slightly better diagnostic sensitivity achieved by Stiffness than BUA or SOS alone [10-16].

The combination of BUA and SOS provides a better indication of bone strength in vitro than either variable alone [17,18]. Until recently the better sensitivity of Stiffness had not been demonstrated conclusively in vivo, although several studies have suggested higher Z-scores for Stiffness than BUA or SOS. In the study by Cepollaro et al [161, the gradient of risk for vertebral fracture using Stiffness was significantly greater than that for BUA or SOS alone. A study by Hadji et al [191 presented at the ASBMR showed that the area under the ROC curve was significantly greater for Stiffness than for BUA or SOS.

Prospective studies have demonstrated an excellent gradient of fracture risk for heel ultrasonometry in older women, but there have been few studies done in patients <65 years of age. Some uninformed critics have even suggested that ultrasonometry might not prove diagnostic in younger patients. Thompson et al [20] presented a retrospective study showing that Stiffness provided a good Z-score (-0.8) in that immediate postmenopausal population. A prospective study by the same group now indicates that Stiffness predicts incident fracture in that age period [21]. The Achilles is the only ultrasonometer documented to predict fracture in the first postmenopausal decade.

There also are an increasing number of studies on younger patients with corticosteroid osteoporosis [12,22,23]. Corticosteroids cause loss of bone, but also increase the risk of fracture at any given BMD level, so fractures typically occur at age 60, rather than after age 70 as is the case in postmenopausal osteoporosis. Blanckaert et al [12] showed that the Z-score for Stiffness was -0.8 in patients compared to matched-controls; this was more diagnostic than spine or femur BMD which had a Z-score of -0.6. Similarly, Oliveri et al 1221 showed a Z-score of -1 .3 for Stiffness compared to about -0.9 for axial BMD. The Achilles is the only ultrasonometer with documented sensitivity in corticosteroid osteoporosis.

Table 2. Comparison of Stiffness in osteoporotic patients to normal controls matched for femur neck BMD. The results are given for normal women within 3 years since menopause and more than 10 years since menopause. Adapted from Yeap et al [15]

Controls
Neck BMD YSM<3 YSM>1 Osteoporotic
<0.6 g/cm²73.5 72.3 60.8
0.6 to 0.7 g/cm²83.1 81.5 71.5

Ultrasonometry of the os calcis provides some independent information on risk of fracture beyond that afforded by BMD itself. Yeap et al [15] stratified postmenopausal women with and without fractures by BMD level and found that Stiffness was about 1 SD lower in the fracture patients even after "BMD-matching" (Table 2). As yet, this advantage has not been translated into a lower composite Z-score. It does mean, however, that the number of abnormal cases (below -2.5 SD) is increased greatly (from ~20% to 30% of postmenopausal women) when both Stiffness and axial BMD are used as diagnostic criteria.

A key factor in all densitometry, including ultrasonometry, is the ability to use the WHO T-scores in assessing women at risk. Most heel ultrasonometers utilize BUA as their output variable, or produce indices such as QUI which depend almost wholly on BUA. However, BUA and QUI decline by only 1 SD (about 1 5%) with age (Figure 1), so that the T-score for BUA with all heel ultrasonometers, including the Achilles, is only -1 at age 65. As a consequence, the WHO criterion for osteopenia is not achieved until that age, and the WHO criterion for osteoporosis (-2.5 SD) is almost never achieved. The Sahara, DTU-One, UBIS, and other similar devices show an average T-score of -1 in the elderly, and the prevalence of osteoporosis is only about 5% in postmenopausal women (Table 3). This compares poorly to the T-score of -1 .6 using femur BMD or Stiffness (Achilles) and a 20% prevalence of osteoporosis [14,24]. Stiffness gives the same prevalence of abnormal cases as axial BMD [24]. Of all heel ultrasonometers, only the Achilles provides T-scores concordant with the WHO criterion of osteoporosis.

Table 3. Prevalence of cases with T-score below -2.5 SD with different measurements

AGE
50-59 60-69 70-79

Axial BMD 5 18 33 Better
Stiffness 4 17 32
Forearm BMD 2 15 52
BUA 2 4 15
QUI/eBMD 2 5 14
Finger BMD 1 2 10 Worse

Ultrasonometry of the os calcis has been shown to give a response to therapy similar to spine and total femur BMD. The precision error of ultrasonometers that use fixed transducers, with a waterbath or a bladder, is about half that of contact ultrasonometers with moving transducers (2% versus 5% in elderly subjects) [25-29]. The "better" precision of imaging ultrasonometers (~2%) is more a function of their using fixed transducers with good coupling rather than better location of the ROI [30]. Contact ultrasonometers cannot accurately measure SOS because they must measure heel width accurately to get a result. The error in heel width measurement is 1 to 2 mm out of 40 mm, so there is an inherent uncertainty of 2 to 5% in SOS measured with contact ultrasonometers. This error is compounded by the large effect of edema on results (5 to 15%) [31]. Even post-exercise edema in the heel adversely compromises both BUA and SOS [32,33]. These systematic errors, as well as the high precision error (4 to 8%), prevent contact ultrasonometers from being used to monitor bone loss or the response to therapy in the individual patient. In contrast, the Achilles can be used to monitor even short-term changes [27].


	Precise Ultrasound Densitometry The Achilles ultrasound densitometer was designed to provide optimal performance for osteoporotic as well as normal subjects. The standard deviation (SD) for x-ray absorptiometry BMD typically is constant or increases with decreasing density so the CV increases 30-100% in osteoporotics (3% vs. 1.5%). In contrast, the SD for Achilles decreases by 30% so the CV is constant or even decreases. Rosenthal³⁴ recently reported the precision for a large group of normal and osteopororic subjects (Table 1). The use of a water bath densitometer is essential for measurement of the elderly osteoporotic subject. Loss of skin and soft tissue elasticity in the elderly subject can affect both the reflection and transmission of ultrasound energy. The improved ultrasound coupling with a properly-designed warer bath densitometer assures optimal precision for elderly subjects. The recent publication by Greenspan¹⁰also shows that Achilles has the best precision for both normal and osteoporotic women (Table 2). Achilles Has 3X Better Precision Not all ultrasound densitometers have sufficient precision to monitor bone changes over time. Water bath densitometers can have better inherent precision due to operator variability, immunity from pressure dependency, and allowance of sufficient time for stabilization. However, they must provide a constant temperature water bath and/or temperature compensation. Earlier ultrasound densitometers only measured the Speed of Sound (SOS) and the Broadband Ultrasound Attenuation (BUA); use of Stiffness, which combines SOS and BUA, provides independence from temperature effects. Stiffness also minimizes the influence of heel width because, as heel width increases, BUA is overestimated and SOS underestimated. The combination of BUA and SOS in Stiffness, coupled with the constant temperature water bath and adequate measurement times, are the major reasons why the Achilles ultrasound densitometer has 3X better precision³⁵ than other ultrasound devices.

REFERENCES

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