Keywords:
Neuroradiology spine, Interventional non-vascular, CT, Imaging sequences, Dosimetry, Image verification
Authors:
D. Brand1, R. Davies1, J. Kew2; 1SA/AU, 2Woodville, SA/AU
DOI:
10.1594/ranzcr2018/R-0115
Results
Region |
Lowest DLP |
Median DLP
|
Highest DLP |
Mean DLP |
Cervical (n=41) |
0.8
|
3 |
14.9 |
3.79 |
**Lumbar (n=141) |
0.9 |
4.8 |
102.4 |
11.42 |
SIJ (n=13) |
1.2 |
3.2 |
26.4 |
6.06 |
Thoracic (n=5) |
5.4 |
7 |
87.9 |
22.82 |
Total: Consecutive 200 patients 9.700
** excludes one case where needle placement DLP was combined with a diagnostic scan.
Scanner |
Lowest DLP |
Median DLP |
Highest DLP |
Mean DLP |
160 slice (n=77) |
0.8 |
2.6 |
29.4 |
3.92 |
**16 slice (n=123) |
1.6 |
5.9 |
102.4 |
10.82 |
** excludes one case where needle placement DLP was combined with a diagnostic scan.
There was a non-significant difference of DLP means between the two 160 slice scanners of 3.21 and 5.15 mGy.cm (p<0.078).
There was a significant difference between the two 16 slice scanners with DLP means of 12.47 and 6.22 mGy.cm (p<.01).
In this study there was a highly significant difference between the mean DLP delivered by the 16 (DLP=10.82) and 160 slice scanners (DLP=3.92; p<0.001).
The radiation dose delivered for both types of scanner is substantially smaller than the published data from other series (DLP 89,
94,
199).
The principle methods used to reduce radiation dose were;
- elimination of CT fluoroscopy and replacement with single sequential acquisitions to adjust needle position
- use of a sub 1cm axial acquisition slice reconstructed as 4 contiguous 0.5-2mm slices to assess needle position
- use of the shortest possible slice acquisition time by sectored scanning and maximum rotation speed to reduce respiratory motion artefact
- use of the thinnest possible slice thickness
- use of lowest possible mA while maintaining needle identification
- acceptance of substantial image quantum mottle,
while needle angle and tip position could still be discerned
Factors resulting in an increased DLP included;
- larger patient size necessitating higher mA and a larger number of acquisitions to achieve needle placement in the target space
- lack of patient cooperation resulting in a larger number of acquisitions to achieve needle placement in the target space
- higher rotation time for 16 slice scanners resulted in a higher average DLP although this was still very low compared to published data
- technical difficulty of needle placement in the target space due to hostile anatomy