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Align the phantom (16 cm or 32 cm as appropriate for the scan protocol) such that the axis of the phantom is at the isocenter of the scanner and centered in all three planes.If this configuration is not accessible in axial mode, use the N x T configuration most closely matching the clinical value.d. Make one exposure in axial mode using the clinical N x T configuration.If the protocol is normally scanned helically, convert this to an axial scan while keeping the remaining technical parameters the same.Note: For pediatric (40-50 pounds) abdomen protocols, some CT scanners report CTDIvol using the 16 cm phantom, while others use the 32 cm phantom.It is imperative that the detector configuration and total beam width used matches the site's clinical protocol (N x T) as closely as possible.At a minimum, the scans performed should include the following protocols: a. Adult Routine Brain b. Pediatric Routine Brain (1 year old) c. Pediatric Routine Abdomen (5 years old; 40-50 lb., approx.a. For adult head protocols, position the 16-cm phantom in the head holder or as heads are scanned clinically.2.3.5.6.

Align the phantom (16 cm or 32 cm as appropriate for the scan protocol) such that the axis of the phantom is at the isocenter of the scanner and centered in all three planes.
a.
For adult head protocols, position the 16-cm phantom in the head holder or as heads are scanned clinically.
b.
For adult abdomen protocols, position the 32-cm phantom directly on the scan table.
c.
For pediatric head protocols, position the 16-cm phantom directly on the scan table.
d.
For pediatric abdomen protocols, position the 16- or 32-cm phantom directly on the scan table.
Note: For pediatric (40-50 pounds) abdomen protocols, some CT scanners report CTDIvol using the 16 cm phantom, while others use the 32 cm phantom. The physicist should select the phantom (16- or 32-cm) that is used by the scanner to report CTDIvol.
2.
Connect the pencil chamber to the electrometer and insert the pencil chamber into the central hole in the phantom. Ensure that all other holes (those at 3, 6, 9, and 12 o’clock positions) are filled with acrylic rods.
3.
Clinical dose evaluation. At a minimum, the scans performed should include the following protocols:
a.
Adult Routine Brain
b.
Pediatric Routine Brain (1 year old)
c.
Pediatric Routine Abdomen (5 years old; 40-50 lb., approx. 20 kg)
d.
Adult Routine Abdomen (70 kg)
4.
Using the appropriate protocol, prepare to acquire a single axial slice at the center of the phantom with no table increment. If the protocol is normally scanned helically, convert this to an axial scan while keeping the remaining technical parameters the same. In addition, see notes below about converting effective mAs or mAs/image to mA, time, and pitch.
All CTDI dose information must be acquired using axial scans.
In multislice CT, CTDI is a function of detector configuration. It is imperative that the detector configuration and total beam width used matches the site’s clinical protocol (N × T) as closely as possible.
If the N × T value used for dosimetry does not exactly match the clinical value, be sure to modify the table increment used in the calculation to yield the same pitch value as used clinically.
5.
Measurements and Data Collection:
a.
Record the CTDIvol reported by the scanner.
b.
Position the phantom as described above.
c.
Place the dosimeter probe in the central position.
d.
Make one exposure in axial mode using the clinical N × T configuration. If this configuration is not accessible in axial mode, use the N × T configuration most closely matching the clinical value.
e.
Record the exposure value reported by electrometer (usually in units of mR).
f.
Repeat the scan two more times and record the exposure.
g.
Repeat steps d–f above with the probe positioned at the 12 o’clock location.
h.
Repeat steps a–g above for each clinical protocol to be tested.
6.
If required by local regulation, hold constant kVp, rotation time, and N × T and then measure CTDI100 as mA is varied.