CT Performance Phantom

Meets guidelines in AAPM Report #1 for performance and quality assurance of CT scanners.

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Description

Meets guidelines in AAPM Report #1 for performance and quality assurance of CT scanners.

The increasing use of computerized tomography (CT) as a diagnostic tool creates the need 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 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! This phantom 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 linespread 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 resealable cavities (from 1″ to 1/8″ dia.) which can be filled with a diluted dextrose or other appropriate solution to provide a low-contrast media. The optional External Resolution and Noise Ring slides snugly over the outside diameter of the tank, allowing whole-body scanner systems to be evaluated.

Specifications

Water Tank: Made of acrylic 8 1/2 " O.D x 8" I.D x 12 3/4" long. Resealable 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, polystryene, and nylon. Density values: polyethylene, 0.95 gm/cc, polystryene, 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 Capintec CT Phantom. For example, the nylon pin in every CT Phantom we manufacture has the same density.
This uniform density among the 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 eight sets of five 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, .05, .04, and 0.2 mm round). In both phantom inserts, the holes are spaced longitudinally on 5 mm centers and vertically on centers equal to twice the hold 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 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. The 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. x 3" long aluminum with tapped hold, allowing pin to be secured to cover plate.
TLD Insert: 1/2" O.D. x 3 1/2" long polystryene rod drilled 3" deep to accept TLD inserts. Resealable 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° apart. Permits whole-body resolution and noise measurements when positioned on the main tank. Inner and outer resolution values are easily determined.
Dimensions: 15 1/2" long x 8 1/2" diameter
Weight: 17.25 lbs.