Mobius AIRO Mobile CT System - Dosage Factors and Image Quality; Conditions of Operation; Dose Information

MI-42-0001 Rev. 19 233
CT USER INFORMATION: Dosage Factors and Image Quality
10.3 Dosage Factors and Image Quality
10.3.1 Conditions of Operation
About this Section This section contains the information for CT users required by FDA 21CFR-1020.33.
kV The generator is capable of delivering kilo voltages from 60
to 125 kV. The typical kV for both body
and head scans is 120 kV.
NOTE: Prior to the initiation of a scan, the Pendant Display shows the CTDI
vol
expressed in units
of mGy and DLP in units of mGy.cm, for head and for body standards. It also displays the phantom
type and diameter on which CTDI
vol
values are based. These values are recorded in the scan data.
Scan Time Per Ring
Rotation
I
n clinical use, the Ring is made to rotate at 30.6 rpm,
resulting in a radiation beam-on time per spin
of 1.92 sec.
mA The X-ray tube is capable of current output from 10 to 250 mA, resulting in tube current – time product
of 19 to 480 mAs. The typical CT condition of operation for an average size adult is expected to be
192 mAs. For Pediatric patients, typical mAs values will be different. See MI-42-005 Application
Guide for Protocols and Principles.
Slice Thickness N = 32 data channels in the z direction (number of tomographic sections produced in a single axial
scan).
T = 1.06 mm acquisition slice thickness (nominal tomographic section thickness) N x T = 33.92 mm
(commonly called Beam Collimation or Detector Configuration)
Table Incrementation: At present, this is set at 48 mm per tube rotation (25 mm/sec) for helical
scanning mode. Future revisions may provide additional speeds.
Pitch Factor
(Helical Scanning
Mode)
Table Incrementation / Beam Collimation = 48 / 33.92 = 1.415
Future versions of the system may be
provided with additional pitch values.
10.3.2 Dose Information
Overview The following dose information is obtained by using Ludlum L-007N PMMA CT dosimetry phantoms
alone on the support platform. Separate dose information is provided for head and body
applications.
The dose information is provided at the following locations:
a. Along the axis of rotation of the phantom
b. Along a line parallel to the axis of rotation and 1.0 centimeter interior to the surface of the
phantom, with the phantom positioned so that the CTDI is the maximum obtainable at this
depth.
The CT conditions of operation are the typical values suggested for CT of the head or body.