Low kilovoltage CT of the neck with 70 kVp: comparison with a standard protocol

Abstract

Background and purpose: CT protocols should aim for radiation doses being as low as reasonably achievable. The purpose of our study was to assess the image quality and radiation dose of neck CT at a tube potential of 70 kVp.

Materials and methods: Twenty patients (7 female, mean age 51.4 years, age range 19-81 years) underwent contrast-enhanced 64-section CT of the neck at 70 kVp (ATCM, effective tube current-time product 614 eff.mAs, range 467-713 eff.mAs). All 20 patients had a previous neck CT at 120 kVp on the same scanner. Two radiologists assessed image quality and artifacts in the upper, middle, and lower neck. Image noise and attenuation were measured, and the CNR was calculated. Effective radiation dose was calculated.

Results: Interobserver agreement regarding image quality of soft tissue for 70-kVp and 120-kVp scans was good to excellent. At 70 kVp, soft tissues were of diagnostic image quality in all scans, whereas the lower cervical spine was not of diagnostic quality in 3 and 4 scans per both readers. No difference was found among 70-kVp and 120-kVp scans for soft tissue image quality in the upper neck, while image quality was significantly better in the middle at 70 kVp (P < .05) and better in the lower third at 120 kVp (P < .05). CNR was significantly higher at 70 kVp in all levels for both readers (P < .001). Effective radiation dose at 70 kVp was significantly lower (0.88 ± 0.2 mSv) than at 120 kVp (1.33 ± 0.2 mSv, P < .001).

Conclusions: CT of the cervical soft tissues at 70 kVp is feasible, provides diagnostic image quality with improved CNR, and reduces radiation dose by approximately 34% compared with a standard protocol at 120 kVp. In contrast, low kVp CT of the lower cervical spine suffers from compromised image quality.

Figures

Fig 1.

37-year-old male patient with follow-up neck CT for lymphoma at 70 kVp (A, C, E) and corresponding previous CT at 120 kV (B, D, F) at 3 anatomical levels. Note the diagnostic image quality with a higher contrast-to-noise ratio of cervical soft tissues at 70 kVp at all levels.

Fig 2.

42-year-old male patient with follow-up neck CT for lymphoma at 70 kVp (A) and corresponding previous CT at 120 kVp (B). Sagittal reconstructions of the cervical spine demonstrate more image noise in the lower spine at 70 kVp in comparison to 120 kVp. Corresponding axial images through the lower neck (level of C7) at 70 kVp (C).

Fig 3.

Measurements of cervical vessel (A) and muscle (B) attenuation, image noise (C), and the calculated contrast-to-noise ratio (D). Mean from both readers was taken for analysis.