Table 1D. Additional experimental data for 30 cm phantom with Gd202S beam filtration at 15 frames/sec
Half
Phantom
Gadolinium
Value
Tube
Input Air
Entrance
Tube
Oxysulfide
Layer
Tube
Pulse
Loading
Kerma
Table
Surface
Voltage
Gd202S
(HVL)
Current Duration
(heat
Rate
Correction Dose Rate
(kVp)
(screen)
(mm Al)
(mA)
(ms)
units)1
(mGy/s)
Factor2
(mGy/s)
780
12.7
65
No screen
2.58
800
15
0.754
18.6
80
No screen
3.23
300
15
360
7.3
0.773
10.3
80
1 fine
3.76
500
15
600
7.1
0.778
10.1
80
2 fine
4.14
700
15
840
7.5
0.785
10.6
95
No screen
3.93
200
15
285
6.8
0.780
9.8
95
1 fine
4.50
400
12
456
4.7
0.802
9.7
95
2 fine
4.89
500
15
713
7.9
0.806
11.4
95
1 fastback
5.34
700
15
998
6.9
0.810
10
95
2 fastback
5.95
400
15
570
3.1
0.820
4.3
110
No screen
4.63
250
10
275
7.5
0.788
11.0
110
1 fine
5.23
200
15
330
5.7
0.804
8.3
110
2 fine
5.67
300
15
495
6.6
0.803
9.6
110
1 fastback
6.19
400
15
660
5.7
0.818
8.2
110
2 fastback
6.98
550
15
908
3.7
0.825
5.2
125
No screen
4.63
200
10
250
7.6
0.790
11.1
125
1 fine
5.96
150
12
225
4.4
0.800
6.6
125
2 fine
6.44
200
12
300
4.7
0.807
6.9
125
1 fastback
7.06
300
12
450
4.7
0.819
6.8
125
2 fastback
8.13
500
12
750
3.9
0.829
5.6
Effective
Dose Rate
(µSv/s)
88.2
74.8
85.7
93.8
98.3
104.2
128.1
128.2
49.2
118.9
104.3
125.3
116.7
93.9
135.8
91.0
100.1
108.3
101.3
Sn td
Contrast
to Noise
Ratio
(CNR)
3.3
2.5
2.6
2.7
2.3
2.3
2.5
2.3
1.4
2.2
1.9
2.1
1.8
1.2
2.0
1.5
1.5
1.4
1.1
Cu td
Contrast
to Noise
Ratio
(CNR)
1.8
1.3
1.4
1.5
1.2
1.2
1.4
1.3
0.8
1.2
1.1
1.1
1.1
0.8
1.2
0.9
0.9
0.9
0.8
1
Heat units of energy represent the relative load on the x-ray tube for this measurement; for comparison it should be divided by the CNR of interest.
2
Table correction factor accounts for x-ray attenuation of the patient couch (table). Air kerma rate was measured at a fixed position with and without the table
in place, and the ratio of the two measurements provided this correction factor to be applied to the phantom input air kerma rate for effective dose
estimation. This was required because the ionization chamber used for air kerma measurement and the phantom were on opposite sides of the couch.