Fluke 18-222 User Manual
Nuclear Associates 18-222 and 18-223
Tissue-Equivalent Mammography Phantom
Instruction Manual
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Contents
Section 1: Introduction .................................................................................................................... 1-1
1.1 Background .................................................................................................................................................................1-1
1.2 The Development of the Standard of Reference .................................................................................1-1
1.3 The Realistically Shaped, Tissue-Equivalent Series of Breast Phantom ...................................1-1
1.4 Clinical Usefulness...................................................................................................................................................1-3
Section 2: Operation......................................................................................................................... 2-1
2.1 How to Use the Mammographic Phantom.............................................................................................2-1
2.2 References....................................................................................................................................................................2-8
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Section 1
Introduction
1.1 Background
The American Cancer Society and American College of Radiology guidelines for the screening of asymptomatic
women have made over 50 million women candidates for mammography. In view of the staggering numbers
involved, it is critically important that simple but reliable methods be developed to assess system performance, to
assure consistent system performance, and to assure consistent production of diagnostically useful images (1, 17).
1.2 The Development of the Standard of Reference
Phantoms for use in mammography should simulate a real breast as closely as possible (2). A list of desirable features
for such a phantom can be found in Section 2, page 2-2. Note that the phantom should be able to test for both
image quality and dose if system performance is to be evaluated. The phantoms must also be easy to use and yield
images that may be unambiguously interpreted.
In developing the tissue-equivalent/realistically shaped phantom:
• Image Contrast may be measured quantitatively with standard densitometers though the use of the
embedded step wedge.
• Dose may be calculated by "TLD" or by ion chamber placed on top of the phantom and converted to average
glandular dose through conversion tables (3.6 and 3.7) in NCRP Report #985 (2). A suggested dose chart is
shown in Figure 2-1.
• Resolution - Simulated tumors and microcalcifications of known size and location are embedded in the
phantom for qualitative evaluation. The smallest microcalcifications and tumors are small enough that they
will not normally be detected.
1.3 The Realistically Shaped, Tissue-Equivalent Series of Breast
Phantoms
Shape
Standard dental modeling techniques were used to obtain molds of the compressed right breast of a volunteer
female subject. This breast is 4.5 cm thick and 18 cm in width.
Materials
Tissue-equivalent resin molding techniques were used. The system of resins used have been developed over the past
six years to permit mimicking of any body tissue at different diagnostic x-ray levels. The elemental composition of the
simulating tissue as compared to Hammerstein's analysis (11) of human tissue is shown in Table 2-1. Also shown in
Table 2-2 are comparisons of linear attenuation coefficients for actual and simulated tissue.
1-1
The basic phantom (Model 18-222) matches the composition of an average firm breast consisting of 50% adipose
tissue and 50% glandular tissue and is realistically shaped. The phantom is suitable for evaluating the mammographic
process in the laboratory as well as for monitoring system performance in the clinic. The phantom may be used for
screen-film mammography or xeromammography. Each molded breast is surrounded with a .5 cm adiposeequivalent tissue. Thus, the glandular portion of the standard phantom is 3.5 cm in thickness.
The materials used in this phantom have been formulated for optimum response in the film-screen mammographic
range of x-ray exposure (24 to 34 kVp), but will generally provide similar results at higher (xeromammographic)
exposure ranges.
The resin materials mimic the photon attenuation coefficients of a range of breast tissues. The average elemental
composition of the human breast being mimicked is based on the individual elemental compositions of adipose and
glandular tissues as reported by Hammerstein (11). See Tables 2-1 and 2-2 for comparative data.
The attenuation coefficients are calculated using the "mixture rule" and the photon mass attenuation and energy
absorption coefficients table of J.H. Hubbell (16).
Optional Size Phantoms
The Model 18-222 Phantom is 4.5 cm in compressed thickness. Other sizes available are 4 cm, 5 cm, and 6 cm
thickness.
Optional Tissue Densities
Densities ranging from 20% glandular/80% adipose to 70% glandular/30% adipose are available on request.
Details
The Standard Phantom (Model 18-222) has embedded details (Figure 2-2) consisting of:
• Seven masses that are 75% glandular and hemispherical in shape.
• A wax insert with embedded nylon fibers.
• The Model 18-222 has an optical density reference zone. This allows OD measurements, which are position
dependent, to be taken from the same area each time. This helps factor out OD variances.
• The Model 18-222 has two edges of beam targets. This enables precise localization of the x-ray beam's edge - for
example, is the machine penetrating the chest wall, or is it not close enough to the chest wall such that
something may be missed in a clinical setting?
• One line pair test target with line pair tests between 5 and 20 line pair/mm.
The Physicist Research Model
• Three tissue equivalent phantoms with removable outer fat layer and with embedded details similar to Model
18-222
- 4 cm - 50/50 (dense)
- 5 cm – 30/70 (normal) (or 4.5 cm - 50/50)
- 6 cm - 20/80 (fatty)
• Three tissue equivalent slab combinations of plates ranging from .5 cm thickness to 2 cm. This permits test
imaging in .5 cm increments from a thickness of .5 cm to 7 cm.
- 30% glandular/70% adipose
- 50% glandular/50% adipose
- 70% glandular/30% adipose
(Model 18-223) includes:
1-2
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