Focal Spot Condition/System Resolution – Annual Quality Control Test
900.12(e)(5)(iii): Focal spot condition. Until October 28, 2002, focal spot condition shall be evaluated either by determining system resolution or by measuring focal spot dimensions. After October 28, 2002, facilities shall evaluate focal spot condition only by determining the system resolution.
900.12(e)(5)(iii)(A)(1)(2)(3)(4)(5): (A) System Resolution.
(1) Each X-ray system used for mammography, in combination with the mammography screen-film combination used in the facility, shall provide a minimum resolution of 11 Cycles/millimeters (mm) (line-pairs/mm) when a high contrast resolution bar test pattern is oriented with the bars perpendicular to the anode-cathode axis, and a minimum resolution of 13 line-pairs/mm when the bars are parallel to that axis.
(2) The bar pattern shall be placed 4.5 cm above the breast support surface, centered with respect to the chest wall edge of the image receptor, and with the edge of the pattern within 1 cm of the chest wall edge of the image receptor.
(3) When more than one target material is provided, the measurement in paragraph (e)(5)(iii)(A) of this section shall be made using the appropriate focal spot for each target material.
(4) When more than one SID is provided, the test shall be performed at SID most commonly used clinically.
(5) Test kVp shall be set at the value used clinically by the facility for a standard breast and shall be performed in the AEC mode, if available. If necessary, a suitable absorber may be placed in the beam to increase exposure times. The screen-film cassette combination used by the facility shall be used to test for this requirement and shall be placed in the normal location used for clinical procedures.
900.12(e)(5)(iii)(B): Focal spot dimensions. Measured values of the focal spot length (dimension parallel to the anode cathode axis) and width (dimension perpendicular to the anode cathode axis) shall be within the tolerance limits specified in Table 1
Table 1. - Focal Spot Tolerance Limit
|Nominal Focal Spot Size (mm)||Maximum Measured Width (mm)||Dimensions Length (mm)|
- Does the condition of the focal spot have to be measured at all possible magnification values?
- What is meant by the term "focal spot condition" and how does it relate to "system resolution"?
- Where in the x-ray field should focal spot size be measured?
- A facility is using more than one type of screen-film combination. Must it perform the QC tests separately for each combination used?
- Has FDA specified a standard method for placement of the high frequency end of the bar pattern when performing the system resolution test?