Article Figures & Data
Figures
- Fig 1.
Comparison images for the same patient who received a left L4–5 facet block, a left L4–5 synovial cyst fenestration, and a left L4 selective nerve root block in both 2009 and 2010. All acquisitions in 2009 were helical, whereas in 2010, only the initial survey-phase CT images were acquired helically. The tube current was reduced from 549 to 149 mA in the survey image, from 84 to 30 mA in the fiducial bead image, from 84 to 50 mA in the guide phases of the study, and from 199 to 50 mA in the postcontrast images. Total examination DLP in 2010 was reduced 91%.
- Fig 2.
Between 2009 and 2010, there were significant reductions in DLP (milligrays per centimeter) for the total procedure as well as survey, guide, and contrast phases for all cases (A) and cervical-only (B) and lumbar-only (C) CT-guided spinal injections (P < .003 for all individual 2009 versus 2010 comparisons) (bar graph = mean ± standard error of the mean). The mean effective dose for cervical-only and lumbar-only CT-guided injections was reduced in 2010 from 9.7 to 1.1 mSv and from 17.5 to 3.3 mSv, respectively. DLP for some phases of the procedure also differed significantly within the same year (see “Results”).
- Fig 3.
Relative contributions from the survey, guide, and contrast phases of CT-guided spinal injections changed substantially between 2009 and 2010. Significant reductions in DLP during the guide phase of the examination in 2010 lowered its contribution to total procedure DLP from 57% to 20%. In 2010, almost 75% of the patient dose came from the initial survey CT images obtained for identifying anatomy relevant to the patient's spinal pain and prescribing the course of needle insertion.
- Fig 4.
Comparison of total examination doses for different CT-guided procedures that involved only 1 specific type of injection (facet joint, selective nerve root, or epidural block) (bar graph = mean ± SD). Between 2009 and 2010, the total dose decreased significantly for all 3 specific types of CT-guided spinal injections (ANOVA, P < .004 for all comparisons). Selective nerve root block procedures were consistently higher in total dose, but this trend only reached statistical significance compared with facet joint block procedures in 2010 (P = .004).
- Fig 5.
Dose reductions were observed for CT-guided spinal injections by individual supervising neuroradiologists (all 2009 versus 2010 comparisons, P < .003) (bar graph = mean ± SD). Comparisons between supervising neuroradiologists in the same year showed only trends toward statistically significant differences (ANOVA, P = .167 for either 2009 or 2010) due to the large variability in total DLP.
- Fig 6.
Lumbar-only procedures varied in the total number of sites (2.2 ± 1.3, 1–7) or levels (1.5 ± 1.0, 1–7) treated per encounter (mean ± SD, range), but the dose reduction observed persisted even when total examination dose (total DLP) was normalized for the number of sites (DLP/site) or levels (DLP/level) injected during the procedure (bar graph = mean ± SD). All 3 ways of analyzing procedural DLP showed approximately 80% reductions between 2009 and 2010 (P < .0001). Similar large dose reductions also persisted for cervical-only procedures when normalized for the number of sites or levels treated (P < .002).
- Fig 7.
Sample images from a 2010 study with aggressive dose reduction during a technically successful CT-guided right C6 selective nerve root block. Only the survey CT images were acquired helically (scan length = 50 mm). The milliampere/DLP (milligrays per centimeter) was 29/20.1, 10/0.5, and 20/1.0 for the survey (A), guide (B), and contrast (C) images, respectively (note, 8 guide series with slightly varying milliamperes or ranges were obtained). Total examination DLP was 28.6 mGy · cm, giving an estimated total effective dose of only 0.17 mSv. This dose is comparable with or lower than that for fluoroscopy-based spinal injections for pain.
Tables
- Table 1:
Group comparisons between patients receiving CT-guided spinal injections in 2009 and 2010a
Patient Group 2009 2010 T Test P Value Age (yr) 55.6 ± 14.0 59.9 ± 14.0 .128 Male 42% (21) 58% (29) NA Injection sites 2.0 ± 1.0 (100) 2.1 ± 1.3 (103) .667 Medial branch blocks 0.1 ± 0.3 (4) 0.1 ± 0.4 (4) 1.000 Facet joint blocks 0.4 ± 0.8 (22) 0.6 ± 1.3 (28) .357 Selective root blocks 1.3 ± 0.9 (63) 1.0 ± 1.0 (49) .118 Epidural blocks 0.2 ± 0.4 (11) 0.4 ± 0.6 (22) .053 Injection levels 1.5 ± 0.7 (77) 1.6 ± 1.1 (81) .589 Cervical levels 0.7 ± 0.8 (35) 0.2 ± 0.6 (12) .001 Thoracic levels 0.1 ± 0.5 (5) 0.1 ± 0.3 (4) 1.000 Lumbar levels 0.6 ± 0.8 (30) 1.1 ± 1.2 (53) .016 Sacral levels 0.1 ± 0.4 (7) 0.2 ± 0.6 (12) .329 Hardware present 24% (12) 14% (7) NA Reported painb 6.2 ± 1.8 (28) 6.3 ± 2.3 (36) .809 Immediate pain decrease 3.9 ± 2.4 4.4 ± 2.6 .320 Procedure time (min) 45.4 ± 19.1 43.1 ± 17.8 .535 - Table 2:
Group comparisons between selected CT-acquisition parameters for patients receiving CT-guided spinal injections in 2009 and 2010a
Parameter Anatomy 2009 2010 T Test P Value Minimum guide-phase tube current (mA) All studies 75.0 ± 61.2 13.4 ± 7.3 <.001 Cervical only 104.0 ± 68.2 16.7 ± 11.2 <.001 Lumbar only 37.7 ± 29.0 11.7 ± 4.9 <.001 Total image seriesb All studies 12.3 ± 5.8 9.7 ± 5.4 .022 Cervical only 14.0 ± 6.1 10.9 ± 4.6 .178 Lumbar only 10.8 ± 3.3 9.3 ± 4.9 .269 Survey scan length (mm) All studies 100.4 ± 36.4 94.5 ± 38.9 .436 Cervical only 90.9 ± 56.6 56.6 ± 20.3 .088 Lumbar only 108.0 ± 103.0 103.0 ± 40.0 .816
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