Spherical lesion phantoms for testing the performance of elastography systems - PubMed (original) (raw)

Spherical lesion phantoms for testing the performance of elastography systems

Ernest L Madsen et al. Phys Med Biol. 2005.

Abstract

A set of three cubic one-litre phantoms containing spherical simulated lesions was produced for use in comparing lesion detection performance of different elastography systems. The materials employed are known to be stable in heterogeneous configurations regarding geometry and elastic contrast identical with (storage modulus of lesion material) / (storage modulus of background material), and regarding ultrasound and NMR properties. The materials mimic soft tissues in terms of elastic, ultrasound and NMR properties. Each phantom has only one value of elastic contrast (3.3, 4.6 or 5.5) and contains arrays of 1.6 mm, 2 mm, 3 mm and 4 mm diameter spherical simulated lesions. All the spheres of a given diameter are arranged in a regular array with coplanar centres. Elastograms of an array made with ultrasound allow determination of the depth range over which lesions of that diameter and elastic contrast can be detected. Two phantoms are made from agar-plus-gelatin-based materials, and one is made from oil-in-gelatin dispersions. The methods for producing the phantoms are described in detail. Lesion detection performances for two ultrasound systems, both operating at about 7.5 MHz and focused at about 5 cm, were quantified with distinctions between the two systems demonstrated. Neither system was capable of detecting any of the 1.6 mm lesions. Phantoms such as these should be useful in research labs that are refining hardware and/or software for elastography.

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Figures

Figure 1

Diagrams showing the planar array of 3 mm and 4 mm diameter spheres (a) and of 1.6 mm and 2 mm diameter spheres in each phantom (b).

Figure 2

View of phantom with planes containing the centres of equal diameter spheres being perpendicular to the figure. In use, the ultrasound scan planed is superimposed on one of these planes.

Figure 3

Diagrams of two-part moulds used to form twelve 4 mm diameter spherical inclusions: (a) side view; (b) view facing hemispherical depressions; (c) two parts of the mould pressed together to form 4 mm spheres.

Figure 4

Mould parts for forming background section A (figure 2) of the phantom. A frontal view (a) and side view are shown of an acrylic plate with an array of equal diameter acrylic hemispheres projecting from one surface. A C-clamp is used to clamp that acrylic plate to the second part of the mould (c) along with bottom constraining plate (d) to define section A.

Figure 5

Moulds for production of background section B. Background section A has been completed and the 3 mm diameter spheres have been implanted in its sockets (cross-hatching). The upper bounding acrylic plate has 2 mm diameter acrylic hemispheres projecting downwards to form sockets for the 2 mm diameter spherical inclusions.

Figure 6

Apparatus used to align the ultrasound scan plane on a plane of spheres with equal diameter and equal elastic contrast and also to allow precisely controlled axial compressions for generating elastograms. See section 5 of the text for a detailed description of its use.

Figure 7

Depth ranges in which spherical lesions were detected on elastograms by human observers using phantom 3 with elastic contrast of 3.3. No evidence of 1.6 mm lesions was present for any scanner. Only the Siemens Antares detected 2 mm lesions. Also, the Siemens system allowed detection of 3 and 4 mm lesions to slightly greater depths than the Aloka system.

Figure 8

Depth ranges in which spherical lesions were detected on elastograms by human observers using phantom 2 with elastic contrast of 4.6. No detection of 1.6 mm lesions occurred. The Aloka SD 2000 system barely detected 2 mm lesions over a 1 cm depth range. The Siemens system somewhat outperformed the Aloka regarding detection of 3 mm lesions, particularly regarding greater depth of detection.

Figure 9

Depth ranges in which spherical lesions were detected on elastograms by human observers using phantom 1 with elastic contrast of 5.5. Again, no detection of 1.6 mm lesions occurred for either system. The Siemens and Aloka systems performed comparably for this phantom which has the highest elastic contrast of the three phantoms. The 4 mm lesions were detected by the Siemens system for the entire depth range where lesions existed, and the Aloka detected the 4 mm lesions over the entire depth except for the most distal cm (8 to 9 cm depth).

Figure 10

Power spectra of the RF data obtained for the Aloka and Antares system. Both spectra are normalized to their maximum values.

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Spherical lesion phantoms for testing the performance of elastography systems - PubMed (original) (raw)