2 Scan Theory
2.1 Dose Deterministic Effects
There is the possibility that in normal use, the patient could be exposed to radiation dose levels
of 1Gy CTDI
100 (peripheral)
or above, at which deterministic effects may become apparent.
Management of the high radiation dose is critical to maintain radiation safety. The available
scan settings concerning radiation dose, air kerma, air kerma rate, radiation quality, and image
quality include: mA, kV, scan time, detector coverage, and SFOV.
The table below provides the scan duration in seconds required to meet 1Gy CTDI
100 (peripheral)
at
200 mA exposure at same scan location. This table assumes 200 mA and provides scan time
as a practical example for an average patient. The product of the scan time shown and 200 mA
yields the mAs required to result in 1Gy CTDI
100 (peripheral)
. Note that for each kV / Aperture /
SFOV combination in the table, any mA and scan time combination that meets or exceeds the
equivalent mAs of this table can also result in deterministic effects of radiation. For obese
patients, the mA may be larger than the practical example shown in the table, and the resulting
mAs should be used to determine the exposure to the patient.
Table 1: Dose Deterministic Effects
Duration of Cine scan(s) at 200 mA required to meet 1Gy CTDI
100 Peripheral
SFOV
Ped Head
Ped Body
Small Head
Head
Small Body
Cardiac Small
Medium Body
Cardiac Medium
Large Body
Cardiac Large
CTDI Phantom 16cm 16cm 32cm 32cm 32cm
Focal Spot XL L S XL L S XL L S XL L S XL L S
70
160
NA 142 142 NA 123 122 NA 253 253 NA 213 213 NA 261 261
140 NA 147 147 NA 126 126 NA 263 263 NA 221 221 NA 273 273
120 NA 153 153 NA 130 130 NA 279 279 NA 234 234 NA 289 289
80 NA 156 156 NA 133 135 NA 303 303 NA 255 255 NA 314 318
40 NA 145 145 NA 124 124 NA 281 281 NA 237 237 NA 292 292
5 NA 88 98 NA 75 84 NA 169 189 NA 143 160 NA 176 197
80
160
NA 99 99 NA 83 82 NA 174 174 NA 142 142 NA 166 166
140 NA 102 102 NA 85 85 NA 180 180 NA 148 148 NA 174 174
120 NA 106 106 NA 88 88 NA 191 191 NA 156 156 NA 184 184
80 NA 108 109 NA 90 91 NA 207 207 NA 170 170 NA 200 202
40 NA 101 101 NA 84 84 NA 193 193 NA 158 158 NA 186 186
5 NA 61 68 NA 51 57 NA 116 129 NA 95 107 NA 112 126
100
160
NA 55 55 NA 46 46 NA 95 95 NA 79 79 NA 87 87
140 NA 56 56 NA 48 48 NA 99 99 NA 82 82 NA 91 91
120 NA 59 59 NA 49 49 NA 104 104 NA 87 87 NA 96 96
80 NA 60 61 NA 50 51 NA 113 113 NA 94 94 NA 105 106
40 NA 56 56 NA 47 47 NA 106 106 NA 87 87 NA 97 97
5 NA 34 38 NA 28 32 NA 64 71 NA 53 59 NA 59 66
Revolution CT User Manual
Direction 5480385-1EN, Revision 1
218 2 Scan Theory
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