Ultralow-dose CT with tin filtration for detection of solid and sub solid pulmonary nodules: a phantom study.
OBJECTIVE
To investigate the diagnostic performance of advanced modelled iterative reconstruction (ADMIRE) to filtered back projection (FBP) when using an ultralow-dose protocol for the detection of solid and subsolid pulmonary nodules.


METHODS
Single-energy CT was performed at 100 kVp with tin filtration in an anthropomorphic chest phantom with solid and subsolid pulmonary nodules (2-10 mm, attenuation, 20 to -800 HU at 120 kVp). The mean volume CT dose index (CTDIvol) of the standard chest protocol was 2.2 mGy. Subsequent scans were obtained at 1/8 (0.28 mGy), 1/20 (0.10 mGy) and 1/70 (0.03 mGy) dose levels by lowering tube voltage and tube current. Images were reconstructed with FBP and ADMIRE. One reader measured image noise; two readers determined image quality and assessed nodule localization.


RESULTS
Image noise was significantly reduced using ADMIRE compared with FBP (ADMIRE at a strength level of 5 : 70.4% for 1/20; 71.6% for 1/8; p < 0.001). Interobserver agreement for image quality was excellent (k = 0.88). Image quality was considered diagnostic for all images at 1/20 dose using ADMIRE. Sensitivity of nodule detection was 97.1% (100% for solid, 93.8% for subsolid nodules) at 1/20 dose and 100% for both nodule entities at 1/8 dose using ADMIRE 5. Images obtained with 1/70 dose had moderate sensitivity (overall 85.7%; solid 95%; subsolid 73.3%).


CONCLUSIONS
Our study suggests that with a combination of tin filtration and ADMIRE, the CTDIvol of chest CT can be lowered considerably, while sensitivity for nodule detection remains high. For solid nodules, CTDIvol was 0.10 mGy, while subsolid nodules required a slightly higher CTDIvol of 0.28 mGy.


CONCLUSIONS
Detection of subsolid nodules is feasible with ultralow-dose protocols.
University Hospital Zurich, Department of Diagnostic and Interventional Radiology/University of Zurich, Zurich, Switzerland.
Katharina
K
Martini
University Hospital Zurich, Department of Diagnostic and Interventional Radiology/University of Zurich, Zurich, Switzerland.
Kai
K
Higashigaito
University Hospital Zurich, Department of Diagnostic and Interventional Radiology/University of Zurich, Zurich, Switzerland.
Borna K
BK
Barth
University Hospital Zurich, Department of Diagnostic and Interventional Radiology/University of Zurich, Zurich, Switzerland.
Stephan
S
Baumueller
University Hospital Zurich, Department of Diagnostic and Interventional Radiology/University of Zurich, Zurich, Switzerland.
Hatem
H
Alkadhi
University Hospital Zurich, Department of Diagnostic and Interventional Radiology/University of Zurich, Zurich, Switzerland.
Thomas
T
Frauenfelder
D000465:Algorithms; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D055613:Multiple Pulmonary Nodules / Q000000981:diagnostic imaging*; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014001:Tin; D014057:Tomography, X-Ray Computed
D014001:Tin