Nuclear Associates 76-700 Digital Subtraction Angiography Phantom Users Manual March 2005 Manual No. 76-700-1 Rev. 2 2004, 2005 Fluke Corporation, All rights reserved. Printed in U.S.A. All product names are trademarks of their respective companies
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Introduction Introduction 1 1.1 Introduction Section 1 Introduction This unique QA test tool provides a reliable, accurate, and easy means of evaluating the digital functions of DSA equipment. * Important performance parameters are measured by a system of five clear-acrylic building blocks: 1 step wedge, 1 bone block, 1 resolution block, 1 artery block, and 1 slot block. Each has a specific function. However, some of the modules can be combined to perform additional tests. For example, the step wedge has two functions: (1) It serves as a contrast measurement wedge, and (2) it "folds" on itself to become a 3-inch thick solid body block. This system versatility assures maximum performance with minimal effort and cost. 1.2 System Components The phantom consists of five clear-acrylic building blocks: 1 step wedge, 1 bone block, 1 resolution block, 1 artery block, and 1 slot block (see Figure 1). Figure 1-1. System Building Blocks 1.2.1 Step Wedge This module tests a machine's contrast range by its ability to visualize all steps. The six acrylic steps are each 2.5 cm high. The top three steps can be "folded" over the bottom three to form a solid block, 20 x 20 x 7.5 cm thick. When used with the slot block, it simulates the patient's body. *Non-digital functions of DSA systems can be checked with conventional fluoroscopic test equipment such as: Fluoroscopic System Resolution Test Tools (07-601/07-619) Rotatable Spoke Test Pattern (07-629) Fluoroscopic Quality Control Test Tool (07-637) Fluoro-Test Tool (07-645) Patient Phantom/Penetrometer System (07-706) 1-1
Nuclear Associates 76-700 Operators Manual 1.2.2 Bone Block This 20 x 20 x 2.5 cm thick piece contains simulated calcium bones (20 x 2.5 cm) in three thicknesses-- 0.5, 1.0 and 1.5 cm. When the bone block is positioned over the other blocks, the subtraction function can be tested by the degree to which the simulated bones remain visible in the final subtracted images. 1.2.3 Resolution Block There are two precision test patterns in this 15 x 20 x 2.5 cm module. The patterns have line-pair groups, from 0.6 to 5.0 LP/mm, with a 0.01 mm lead thickness (Test Pattern 07-527). 1.2.4 Artery Block This 15 x 45 x 2.5 cm piece contains three iodine filled simulated arteries whose width and depth are 1, 2 and 4 mm respectively. Each artery includes simulated stenoses and aneurysms that are one-fourth, onehalf, and three-fourths of the individual artery's width. The iodine concentration is 15 mg/ ML. The module also has three circles 1 cm diameter, each with a different iodine content (1.5, 3 and 6 mg/cm 2 ) for testing linearity. Iodine concentrations of 150 mg per ML and 300 mg per ML are also available. 1.2.5 Slot Block The center of this 20 x 20 x 7.5 cm thick module has a slot that holds and positions the resolution and artery sections. The block is also used to increase "body" thickness by 7.5 cm. 1.2.6 Blank Block This is not a separate module but part of the elongated artery block. The blank portion can be positioned in the slot block to make the mask image. 1.3 Directions 1.3.1 General 1. Program a delay of 10 to 15 seconds between the mask and image exposures. Use this same delay for all images. 2. The first time you use the phantom, find and record the best technique to use for each test. Include all details such as aperture, geometry, gain, kilovoltage, current and exposure time. Continue to use these same values when repeating the tests. 3. Use the 6-inch image intensifier mode, or whichever mode is used most often. Always use the same mode for testing. 1.3.2 Wedge Images For testing video system stability, contrast, dynamic range and system noise. 1. Place the step wedge (6 steps) on the table (see Figure 1-2), with steps at 45 to the video scan (raster) lines. Figure 1-2. Step Wedge (unfolded). 1-2
Introduction Directions 1 2. Make sure the image intensifier grid is in place. 3. Use a standard, repeatable geometry for the exposure (e. g., an 80 cm source-to-image-intensifier distance and a 20 cm object-to-image-intensifier distance). Position the wedge, using the fluoro mode. A "scout" or test image will indicate when the correct video level has been set. 4. Make two exposures of the wedge--one for the mask and one for the test. Subtract one from the other. Make a film of the subtracted image. Note that all films can be made at one time--at the end of the testing, if desired. 1.3.3 Resolution Test Images For checking low-contrast spatial resolution: 1. Place the phantom on the table as shown in Figure 1-3. Do not use the bone block. 2. Adjust the object-to-image-intensifier distance to 15 cm and center the phantom. 3. Make sure that the image intensifier grid is in place. Figure 1-3. Blocks Arranged for Testing Resolution Figure 1-4. Artery Block Patterns 1-3
Nuclear Associates 76-700 Operators Manual 4. With the blank end of the artery block inserted in the slot, make a mask exposure. You have only 10 or 15 seconds to remove the artery block and insert the resolution block so that the patterns are centered in the slot block. Allow the image exposure to be made. 5. Subtract the mask image from the resolution image. Make a film (enlarge the image with the zoom control, if desired). Note that the image perpendicular to the scan or raster lines is the image to be examined. Because of the visibility of the raster lines, the image of the pattern that runs parallel to them may give false readings. Nevertheless, such a reading may be valuable. 1.3.4 Artery Detectability Images For checking the low-contrast iodine image visibility and linearity and quality of subtraction (see Figure 1-4). 1. Set the standard phantom up as in Figure 1-3, and add the bone block to the top of the phantom. Be sure that the direction of the simulated bones is perpendicular to that of the iodine patterns and parallel to the long dimension of the insert block itself. 2. Keep the image intensifier grid in place if it is normally used clinically. If not, make sure it is removed. 3. With the blank end of the artery-iodine block inserted in the slot, make a mask exposure. You have 10 or 15 seconds to push toe block through so that the artery pattern is in place. Allow the image exposure to be made. 4. Subtract the mask image from the artery image. Make a film (enlarge various parts of the image with the zoom control, if desired). 5. The lack of prominence of the bone images in the subtracted image is a measure of the subtraction effectiveness. 6. Make another subtraction image, exactly as in steps 1 to 3, but without the bone block. 7. With a densitometer, measure the film densities of the centers of the three 1cm circles that contain 1.5, 3 and 6 mg/cm 2 iodine. 8. Subtract the density readings of each iodine concentration from that of the next higher concentration, obtaining D(6) - D(3), and D(3) - D(1.5), where "D" is the density reading. 9. The two differences would be equal (approx. 0.3) were it not for unavoidable non-linearity such as beam hardening by the iodine, scattering, and film H-D curve non-linearity, among other factors. However, such measurements (made as part of a QA procedure) can be compared with reference measurements made earlier, when the system is known to be operating satisfactorily. Of course, the measurements must be made under precisely the same conditions of technique, using the same film, etc. Note that problems with either the hard copy camera and or the film processor might also result in changes in the density differences. 1.3.5 Exposure Measurements Phantom entrance and exit exposure measurements can be make using the 06-526 RAD-CHECK PLUS X-Ray Exposure Meter or an equivalent instrument. Use the technique (kvp, tube current, and exposure time) that is normally used for quality control measurements. 1. Screw the four steel legs into the threaded holes in the slot block, and stand the block on a table. Place the blank end of either the artery or the resolution block into the slot. Finally, position the folded step wedge on the slot block. Do not use the bone block. 2. Set the technique at 80 kvp and 10 mas--or at your normal clinical settings, as desired. Do not use the grid. 3. Entrance and exit exposures are made with the RAD-CHECK or ion chamber placed above and below the phantom. The location of the radiation source will determine whether the measurement is the entrance or the exit exposure. 1-4
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