Evaluation of low-dose dual energy computed tomography for in vivo assessment of renal/ureteric calculus composition.
OBJECTIVE
This study aimed to assess the accuracy of low-dose dual-energy computed tomography (DECT) in predicting the composition of urinary calculi.


METHODS
A total of 52 patients with urinary calculi were scanned with a 128-slice dual-source DECT scanner by use of a low-dose protocol. Dual-energy (DE) ratio, weighted average Hounsfield unit (HU) of calculi, radiation dose, and image noise levels were recorded. Two radiologists independently rated study quality. Stone composition was assessed after extraction by Fourier transform infrared spectroscopy (FTIRS). Analysis of variance was used to determine if the differences in HU values and DE ratios between the various calculus groups were significant. Threshold cutoff values to classify the calculi into separate groups were identified by receiver operating characteristic curve analysis.


RESULTS
A total of 137 calculi were detected. FTIRS analysis differentiated the calculi into five groups: uric acid (n=17), struvite (n=3), calcium oxalate monohydrate and dihydrate (COM-COD, n=84), calcium oxalate monohydrate (COM, n=28), and carbonate apatite (n=5). The HU value could differentiate only uric acid calculi from calcified calculi (p<0.001). The DE ratio could confidently differentiate uric acid, struvite, calcium oxalate, and carbonate apatite calculi (p<0.001) with cutoff values of 1.12, 1.34, and 1.66, respectively, giving >80% sensitivity and specificity to differentiate them. The DE ratio could not differentiate COM from COM-COD calculi. No study was rated poor in quality by either of the observers. The mean radiation dose was 1.8 mSv.


CONCLUSIONS
Low-dose DECT accurately predicts urinary calculus composition in vivo while simultaneously reducing radiation exposure without compromising study quality.
Department of Radiodiagnosis, Postgraduate Institute of Medical Education and Research (PGIMER), Chandigarh, India.
Harshavardhan
H
Mahalingam
Department of Radiodiagnosis, Postgraduate Institute of Medical Education and Research (PGIMER), Chandigarh, India.
Anupam
A
Lal
Department of Urology, Postgraduate Institute of Medical Education and Research (PGIMER), Chandigarh, India.
Arup K
AK
Mandal
Department of Urology, Postgraduate Institute of Medical Education and Research (PGIMER), Chandigarh, India.
Shrawan Kumar
SK
Singh
Department of Biophysics, Postgraduate Institute of Medical Education and Research (PGIMER), Chandigarh, India.
Shalmoli
S
Bhattacharyya
Department of Radiodiagnosis, Postgraduate Institute of Medical Education and Research (PGIMER), Chandigarh, India.
Niranjan
N
Khandelwal
D000328:Adult; D001031:Apatites / Q000032:analysis; D002129:Calcium Oxalate / Q000032:analysis; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D007669:Kidney Calculi / Q000737:chemistry / Q000000981:diagnostic imaging* / Q000473:pathology; D017616:Magnesium Compounds / Q000032:analysis; D008297:Male; D008875:Middle Aged; D010710:Phosphates / Q000032:analysis; D011446:Prospective Studies; D011829:Radiation Dosage; D000069877:Struvite; D014057:Tomography, X-Ray Computed / Q000379:methods; D014514:Ureteral Calculi / Q000737:chemistry / Q000000981:diagnostic imaging* / Q000473:pathology; D014527:Uric Acid / Q000032:analysis; D055105:Waist Circumference; D055815:Young Adult
D001031:Apatites; D017616:Magnesium Compounds; D010710:Phosphates; C016189:whewellite; D002129:Calcium Oxalate; D014527:Uric Acid; C030782:carboapatite; C016188:weddellite; D000069877:Struvite
Radiation dosage; Urolithiasis; X-ray computed tomography