3. E.M. Coppenrath, R. Staudenmaier, C. Becker-Gaab, U. Szeimies, K. Hahn
Low Dose Computed Tomography (LDCT) as an Alternative to Conventional Radiography (CR) for Paranasal Sinuses Imaging
C.-P. Wallner
E.M. Coppenrath, R. Staudenmaier, C. Becker-Gaab, U. Szeimies, K. Hahn

4. Introduction
It has become increasingly common to obtain CT scans of the sinuses when screening for the presence of sinusitis as well as prior to fibreoptic endoscopic sinus surgery (FESS) 5;6
Consequently, the investigation imparts a radiation dose to the patient and in particular to the eye
Such a radiation dose is a possible source of morbidity although it is significantly below the critical dose for cataracts 6;9

5. Purpose
Due to ALARA doses should be „as low as reasonable achievable“ at the best diagnostic value
Since the dose from LDCT is still higher than with conventional paranasal sinus imaging, it is worthwhile evaluating and comparing the doses and the diagnostic efficacy of these main imaging procedures

6. Methods
A retrospectiv study was carried out on 50 consecutive patients suggestive of sinusitis
All patients were radiographically examined with plain sinus X-rays and LDCT within three days
All the LDCT examinations were carried out at 50 mA / 120 kV with 4 mm slices
CR was carried out at 80 kV in om / of projection

7. Methods Picker PQ 6000 CT coronal view om / of projection sequential
slices
4 mm slice thickness
50 mA
120 kV
Siemens Lysholm / Polydoros 80S / Megalix
om / of projection
80 kV

8. Methods
For dose measurment LDCT of the paranasal sinuses as well as CR was simulated using an Alderson-Rando phantom
LiF-TLDs were placed on each eyelid, in the lens position and on the thyroid gland
Examinations were blinded and hard copies were reviewed independently in random order by an experienced radiologist and otorhinolaryngeologist to compare the findings
The results were correlated with endoscopic and surgical findings

9. Alderson-Rando Phantom

10. Reducing mA
Imaging paranasal sinuses as high contrast regions reducing the mA is possible without loss of diagnostic quality 6
Although noise, measured by the standard deviation of the CT numbers, goes up in LDCT the increasing graininess of low mA sections does not induce errors of interpretation 4;8
Only in cases of extensive sinus disease, the thickness and integrity of the ethmoid septa is sometimes more difficult to evaluate on LDCT 4

11. massive polyposis

12. „mA-Independence“ in High Contrast Regions

13. „mA-Dependence“ in Low Contrast Regions

14. LDCT vs. CR
LDCT and CR demonstrated equal diagnostic value in 23 patients
In 27 patients the following additional entities could be proved with LDCT ( = n )
mucosal hyperplasia polyposis 8
fluid retention bone lesion 4
bullous concha infindibulum* ( *obstruction )

15. LDCT- vs. CR-Observations Correspondence
frontal and maxillary sinuses concordance 75% ( tendency to underread plain films )
ethmoid sinuses concordance 74% ( tendency to overread plain films )
lower nasal compartment concordance 61% ( tendency to overread plain films )
olfactory recess concordance 69%

18. Imaging-Quality CR LDCT ethmoid sinuses 2.6 1.6
frontal sinuses
ethmoid sinuses
maxillary sinuses
sphenoidal sinuses
olfactory recess
1 = good ; 2 = normal ; 3 = poor ; significantly better ( p < 0,05 ; paired sign test )

19. Diagnostic Efficacy / Costs
LDCT demonstrates any obstruction, the extent of disease and offers a detailed evaluation of the structures.
In all cases, the exact extent of the disease was correctly assessed on each LDCT examination with no false negative study (according to endoscopic or surgical findings)
Interobserver variability : %
Conventional Sinus Imaging ~ $ 30
Sinus CT ~ $ 200

20. LDCT- vs. CR-Doses
The lens dose in LDCT examination was about 30 times higher than in conventional imaging.
The corresponding LDCT surface dose was times higher
LDCT CR (CT)
overall cGy cGy
lense cGy cGy (87 cGy)
eyelid cGy 1.2 cGy
thyroid gland cGy cGy.

21. Conclusion
We show that mA values and consequently the radiation dose, can be considerably reduced without adversely affecting the diagnostic quality of the examination
We conclude that plain films are unreliable and no longer routinely indicated for the evaluation of nasal and paranasal sinus disease 3

22. Conclusion
When radiographic evaluation is indicated, a limited LDCT series of about 20 slices is the technique of choice
It provides superior information with a negligible higher radiation dose to patients at reasonable costs 2
LDCT is the gold standard for exact delineation of inflammatory sinus disease, especially before endoscopic surgery (4)

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