Objective: At the high kVp values used in CT scanning, almost all inte
ractions in soft tissues occur by Compton scattering. By lowering the
kVp close to the k-edge of calcium, beam attenuation by calcium will b
e greater and will be reflected as an increase in density reading (DR)
. The presence of calcification in solitary pulmonary nodules (SPNs),
and thus an implied benign etiology, is currently being diagnosed on C
T by using reference phantoms. We explored the possibility of utilizin
g low kVp (i.e., 80 kVp) to detect the presence of such calcification
in SPNs, thus obviating the need for expensive and cumbersome referenc
e phantoms. Materials and Methods: We first tested this phenomenon of
photoelectric interaction by CT and its effect on DRs by scanning vari
ous dilutions of calcium bicarbonate solution at the standard 140 kVp
and at a lower, 80 kVp, setting. After confirming the hypothesis, we c
onducted a prospective clinical study of 27 consecutive SPNs and scann
ed them at 140 and 80 kVp to detect the presence of calcification by m
easuring their DRs at both kVp values. Results: All calcium solutions
showed an increase in DR on the 80 kVp scan. Of the 27 nodules, 11 (41
%) showed an increase in DR, suggesting the presence of calcification:
10 (91%) were benign, and 1 (9%) was malignant. Conclusion: Our study
demonstrates that dual kVp CT could be reliably used to identify calc
ifications in SPNs, very similar to the use of the reference phantoms
currently being applied for the purpose.