Pacific Northwest X-Ray Inc.

       Harry B. Rusk CT Performance Phantom.       


Meets Guidelines in AAPM Report #1 For Performance Evaluation and Quality Assurance of CT Scanners

This ONE phantom evaluates...
  • Noise
  • Spatial Resolution
  • Sensitivity (Low Contrast Resolution)
  • Absorbed Dose
  • Size Dependence
  • Contrast Scale
  • Slice Thickness
  • Alignment
  • Linearity

  • With the increasing use of computerized tomography as a diagnostic tool, the need has arisen for an efficient means of evaluating the performance of the CT scanners now in use. Recognizing this requirement, the American Association of Physicists in Medicine has established the AAPM Task Force on CT Scanner Phantoms. Its goals are to define CT scanner performance and present practical methods of performance testing through the utilization of special phantoms. This phantom design is based on the guidelines presented in Report #1 of the Task Force and approved by the AAPM

    The modular CT Performance Phantom offers the CT user a single system with which to measure nine performance parameters. ONE PHANTOM DOES IT ALL! It permits the routine standardization of alignment, beam width, spatial uniformity, linearity/contrast, spatial resolution, linespread, noise, size independence, and absorbed dose. All components of the phantom are housed in a compact, transparent tank which holds the system together in the correct orientation.

    The phantom consists of an 8-1/2" diameter acrylic tank containing a beam width insert, a spatial resolution and line-spread block, a high-contrast insert, and a means for inserting alignment pins and/or TLD holders. Additionally, a 1/4" thick Teflon band, positioned at the base of the tank and concentric to the 8" internal diameter, simulates human bone. Attached to the base of the tank is a low-contrast section with re-sealable cavities (from 1" to 1/8" diam.) which can be filled with a diluted dextrose or other appropriate solution to provide a low-contrast media. An optional external resolution and noise ring slides snugly over the outside diameter of the tank, allowing whole-body scanner systems to be evaluated.


    Water Tank: Made of acrylic, 8-1/2" O.D. x 8" I.D. x 12-3/4" long. Re-sealable with fill and drain ports. Low-contrast detectability block is attached to base.

    Linearity and Contrast Insert: 7-1/2" O.D. x 2-1/2" long. Contains 1" diameter contrast pins of polyethylene, acrylic, polycarbonate, polystyrene, and nylon. Density values: polyethylene, 0.95 gm/cc; polystyrene, 1.05 gm/cc; nylon, 1.10 gm/cc; acrylic, 1.19 gm/cc; polycarbonate, 1.20 gm/cc.

    The contrast pins in each CT Performance Phantom are identical in density to the contrast pins of similar material in

    every other Nuclear Associates CT Phantom. For example, the nylon pin in every CT Phantom of our manufacture has the same density. This uniform density among all Nuclear Associates phantoms provides the user with a standard for comparing the performance of different scanners.

    Resolution Insert: 7-1/2" O.D. x 2-1/2" long with 6" diameter solid acrylic block. In the model 76-410-4130 the block has 8 sets of 5 holes (1.75, 1.5, 1.25, 1.00, .75, 0.61, 0.5 and 0.4 mm round). In the model 76-410--4132, the block has nine sets of five holes: 1.75, 1.5, 1.25, 1.00, .75, 0.61, 0.5, 0.4, and 0.2 mm round. In both phantom insserts, the holes are spaced longitudinally on 5-mm centers and vertically on centers equal to twice the hole width. All cavities are filled with air. The 6" block is sectored 1-1/4" out on radius. Insert contains 0.014" stainless steel wire positioned longitudinally to the insert plates. The wire allows simple computation of linespread functions. A sectored 1-1/4" portion of the main 6" block permits an edge gradient to be measured.

    Beam Width Insert: 7-1/2" O.D. x 3-1/2" long. Contains three 0.020" x 1.00" aluminum strips angled at 45 degrees, positioned on the center line and displayed vertically. A simple, direct calculation permits the accurate measurement of beam width. Adjacency is determined merely by a double exposure of two adjacent frames.

    Low-Contrast Extension: 8-1/2" O.D. x 2-3/4" long solid acrylic block. Has two each of the following 2-1/4" deep cavities; 1", 3/4", 1/2", 3/8". 1/4" and 1/8" diameter, spaced twice the appropriate diameter apart, one row of cavities on each side of the center line. Cavities with screw-locking sealing ports are easily filled with dextrose or sodium chloride solutions of various densities. User may adjust densities to any value suitable for the scanner. Typically, 2% or 3% differentials in density between cavities are used.

    Alignment Pin: 0.25" O.D. 3" long aluminum with tapped hole, allowing pin to be secured to cover plate.

    TLD Insert: 1/2" O.D. x 3-1/2" long polystyrene rod drilled 3" deep to accept TLD inserts. Re-sealable cavity. Tapped on other end to allow mounting to cover plate.

    External (Whole-Body) Resolution and Noise Ring: Annulus 12" O.D. x 8-1/2" I.D. x 2-1/2" long contains the same hole pattern as the Resolution Insert, at two locations 90 degrees apart. Permits whole-body resolution and noise measurements when positioned on the main tank. Inner and outer resolution values are easily determined.

    The CT-SSP Insert (Model 76-412) (Slice Sensitivity Profile) Point Response Phantom can be used as a stand-alone phantom or as an insert with the AAPM CT Performance Phantom. The AAPM CT Performance Phantom meets the guidelines in AAPM Report #1 for Performance Evaluation and QC of CT Scanners. The AAPM CT Performance Phantom is described in the report by the AAPM Task Force on CT Scanner Phantoms. The acrylic and closed-cell foam ball bearing size is 0.010 inch, diameter is 7.50 inch, width is 3.50 inch, and weight is 0.825 lb.

    Low-Contrast CT Resolution Insert (Model 76-421) The insert consists of an almost-water-equivalent plastic disc, 201 mm Θ x 25 mm thick, protected on both sides by clear plastic. The resolution targets are a series of water-filled holes from 2.5 to 7.5 mm Θ, in 0.5 mm steps. For each target size, the center-to-center distance between holes is twice the hole diameter to ensure meaningful resolution testing. The inserts 25 mm thickness eliminates alignment problems. Dimensions are 201.6 cm x 32.5 cm thick. Weight is 1 lb.

    Dimensions: 15-1/2" long x 8-1/2" diam.
    Weight: 17-1/4 lbs.

    *Described in a report by the AAPM Task Force on CT Scanner Phantoms approved by the American Association of Physicists in Medicine (AAPM).

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    Computerized Tomography Performance Phantom
    with Resolution Insert (to 0.4mm)

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