P UBLIC Law passed by the Congress in 1969 and often referred to

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1 \OL. 117, No. A PHANTOM FOR THE EVALUATION OF TECHNIQUES AND EQUIPMENT USED FOR ROENTGENOGRAPHY OF THE CHEST* By E. DALE TROUT, D.SC., and JOHN P. KELLEY, B.S. CORVALLIS, P UBLIC Law passed by the Congress in 1969 and often referred to as the black lung law established provisions for roentgenographic examinations of approximately ioo,ooo active coal miners. These examinations were to be carried out in approved facilities of which there are presently about 270. If there is to be any uniformity of roentgenographic quality, some test object that can be sent to these facilities is needed. It seems reasonable to assume that as such programs move into other areas of industrial medicine, there will be a sustained need for some means of evaluating roentgenologic procedures used in such studies. Surely, there must be some common denominator for roentgenographic quality if any long-time, generalized effects are to be reported for epidemiologic purposes. A roentgenogram of less than good quality may be usable for a single, local determination made by a single physician. It is not adequate for a mass study where current findings are to be reported by a number of readers. It is even less acceptable for inclusion in a system subject to periodic review over a period of years. Test objects for purposes such as that considered here have great value. Patients are not suitable, for it is virtually impossible to select at each facility a patient having common characteristics. Then, too, there is always the charge that such patients are receiving unproductive exposure. In addition, a reproducible test object can be used over a period of years to evaluate and incorporate new technology and new materials since the original conditions can * Presented at the Seventy-third Annual Meeting of the American Roentgen Ray Society, Washington, D. C., October 3-6, OREGON always be reproduced at any time and at any location. Since aluminum test blocks have been widely used, first thoughts naturally are given to that material. For many applications, one would like to use a material providing scattering comparable to that of tissue, but aluminum does not meet this requirement. Water or some of the tissue equivalent materials could be used. A stepped water phantom would involve a complicated container. The tissue equivalent plastics are sometimes difficult to obtain and are not inexpensive. For that reason, a readily available plastic with scattering characteristics not too different from tissue was selected. DEVISE OF TEST PHANTOM The test phantom that we have devised consists of 10 sheets of inch cast thermoplastic acrylic resin, Plexiglas-G. The Plexiglas-G that we have used has what the manufacturer calls Class A tolerance, inches, -o.o8o inches and a nominal weight of 4.62 pounds per square foot. The sheets are 6 inches wide and, since each step is i inches long, the total length is i5 inches. When the phantom is exposed employing the factors routinely used for a chest patient measuring cm., the phantom provides the range of film densities found in a chest roentgenogram. A readout of the densities of the steps can be plotted against the step number to provide a graph that can be compared with another graph made under known and controlled conditions. Such a comparison provides information indicative of processing The work upon which this publication is based was performed pursuant to contract FDA with the Bureau of Radiological Health, Public Health Service, Food and Drug Administration, and the National Institute for Occupational Safety and Health, Department of Health, Education and Welfare. 77

2 772 E. Dale Trout and John P. Kellev AIRIL, 1973 SHARP FACE PB SER NO ALL DIMENSIONS IN INCHES tic. 1. I)rawing of phantom, front view. procedures as well as exposure factors. One of the major problems in the black lung program lies in the fact that many of 3RASS HANDLE - DIA NO 10 EYEBOLT HANDLE BRACKET NO.8* I MACHINE SCREW PLEXIGLAS ROO-2 PCS the facilities involved are used for general roentgenography. As a result, the geometry that results from re-positioning the tube leads to some pretty terrible geometry due to the fact that rigid stops, markers, etc., have never been provided. To get an evaluation of the geometry used, a lead pin is embedded in the top of the phantom and a ring is embedded in tile bottom of the thickest step. The positions of the pin and ring are such that a 72 inch source film distance and with i inch space between the film and tile face of tile cassette holder, the image of tile pin will be centered in the ring if the source is centered to the film and at right ALL DIMENSIONS IN INCHES 11G. 2. Drawing of phantom, side view. FIG. 3. Photograph of phantom.

3 \OL. 117, No. 4 Evaluation of Roentgenographv of the Chest I I..) angles in both planes. The use of correct geometry is very critical when grids are used, especially a grid of high ratio. In facilities where equipment is of limited capacity, there may be a tendency to cheat I ic.. Photograph of phantom and cassette holder. on the required 72 inch source-film distance. In the top of the thickest step are 2 lead bars, 3/32 mdl square and 3/8 inch long. When a 72 inch distance is used tile spacing between the inner images of the FiG. 5. Roentgenograms of phantom: 70 kvp, i mas, no grid; 100 kvp, 10 mas, 6:1 grid; iig kvp, 7.5 mas, 8 :i grid; 130 kyp, 5 mas, 10:1 grid.

4 774 E. Dale Trout and John P. Kellev APRiL, d 2.! U, z w I I I I DENSITY VS STEP PHANTOM A MEDIUM SPEED FILM AND SCREENS 72 INCH SOURCE FILM DISTANCE - 7OkVp.I5mAs, No Grid x.iookvp,iomas, 61 GrId kvp,7.5mas,&i Grid kvp, 5.0 mas, 01 Grid g I STEP IL NUMBER 0,0 9 B ( b DI 3 Fic. 6. 1)ensity c s. step number for phantom roentgenograms. bars is 10 cm. A measurement of this distance can be used to confirm compliance and if necessary to calculate the actual distance used. To record gross lack of roentgenographic detail usually associated with poor screen contact, pieces of brass wire mesh of o and 6o mesh are mounted on steps, 6 and 7. No great significance is attached to their use for other than detection of a gross condition such as poor screen contact or movement of some mechanical structure during exposure. Since the phantom weighs is pounds and has a very smooth surface, a hinged handle has been provided. Figures i and 2 provide information as to construction and dimensions. Figure 3 is a close up photograph and Figure shows the phantom in place in front of a cassette holder. The Plexiglas-G sheets have lengths of i4, 3, 4, 6, 74, 9, io4, 12, 134, and 15 inches. The 4 inch sharp face lead numbers for step identification and serial number and the 4 inch hair line lead numbers for brass mesh identification are placed in holes drilled in the Plexiglas and the holes filled with a clear polyester casting resin. The 2 lead bars, the lead pin and the ring are also placed in holes drilled in the Plexiglas and embedded in clear polyester casting resin. The brass wire mesh is placed on the surface of the Plexiglas and held in place by a thin coat of the casting resin. After all parts have been assembled on or in the Plexiglas, the sheets are assembled and clamped in place, and a small amount of Plexiglas solvent cement (dichloroethane) is placed along the junction of each of the sheets. EXPERIMEN IAL STUDIES In addition to providing a fast and simple evaluation of a facility, the phantom is useful for experimental studies.

5 VOL. 117, No. Evaluation of Roentgenography of tile Chest G. 8. Roentgenograms of phantom: 105 kvp, 10 mas, 8:i grid; 115 kvp, 7.5 mas, 8 :i grid. An example of one such study is that made on the use of grids of different ratios. There is, of course, general agreement that 100 line grids should be used. The agreement as to the value of a grid and the ratio to be used has been the subject of a great deal of discussion. The purpose of a grid is to reduce scattered radiation. There is a tendency in chest roentgenography when using a grid to increase kilovoltage in order to retain a short exposure time. If the kilovoltage is increased, the scattered radiation rate and energy increase, and, be\ond a certain point, the contrast with a grid is less than would have been provided b a non-grid technique. To develop some information on what this kilovoltage might be, we studied 100 line grids having ratios of 6:1, 8:1 and 10:1. The roentgenograms and techniques without a grid and with the 3 grids are shown in Figure. The exposure in milliampere-seconds lies within the ranges generally found in use with single-phase equipment. It will be seen that roentgenograms using 70 kvp without grid are comparable with those using a grid when 100 kvp is used with a 6:1 grid, 115 kvp when an 8:i grid is used and 130 kvp when a 10:1 grid is used. When the roentgenographic density of the steps is plotted against the step number (i.e., thickness) as shown in Figure 6, it will be seen that there is good agreement. Figure 7 shows roentgenograms made on the same individual using the techniques employed with the phantom. Again it will be seen that the results are comparable. It seems reasonable to assume that grids of any ratio can be used to produce acceptable results if the kilovoltage is adjusted for the grid ratio. In the examples shown, the contrast is comparable with that obtained without grid. If contrast is to be increased through the use of a grid, some lower kilovoltage with an increase in milliampere-seconds must be used. To illustrate this, Figure 8 shows for comparison a roentgenogram madeusingan 8:i grid at 115 kvp and 7.5

6 776 E. Dale Trout and John P. Kellev APRIL, 1973 I I I I DENSITY VS STEP PHANTOM A IO5kVp, lonias, 8IGrid o----o 115 kvp,7.5mas,8igrjd / / STEP NUMBER 105 kvp 10mM / 8 I GRID.-.-_ I - I /0/ I milliampere-seconds and a roentgenogram 3.. made with the same grid reducing the kilovoltage to 105 kyp and increasing the ex- MEDIUM SPEED FILM AND SCREENS 72 INCH SOURCE-FILM DISTANCE posure to 10 milliampere-seconds. As would 3. be expected, the reduction in kilovoltage leads to an increase in contrast as shown in Figure 9, where density is plotted as a function of step number. There is, of course, a 2.. slight reduction in latitude. Figure 10 shows roentgenograms made on the same individual using the techniques employed with the phantom. Similar studies are currently underway using three-phase, 12 pulse and battery powered equipment. SUMMARY - A test pilantom that is useful for evaluation of procedures in chest roentgenography has been made. It is not expensive, the or materials are generally available and its use to evaluate a technique or a facility is 115 kvp 7.5 mm 8 l GRID tic. 10. Chest roentgenograms: 105 kvp, 10 mas, 8:i grid; 115 kvp, 7.5 mas, 8:i grid. not complicated E. Dale Trout, D. Sc. Oregon State University tic.. 1)ensitv : s. step number for X-Ray Science and Engineering Laboratory phantom roentgenograms. Corvallis, Oregon 97331