Noninvasive differentiation of uric acid versus non-uric acid kidney stones using dual-energy CT.
OBJECTIVE
To determine the accuracy and sensitivity for dual-energy computed tomography (DECT) discrimination of uric acid (UA) stones from other (non-UA) renal stones in a commercially implemented product.


METHODS
Forty human renal stones comprising uric acid (n=16), hydroxyapatite (n=8), calcium oxalate (n=8), and cystine (n=8) were inserted in four porcine kidneys (10 each) and placed inside a 32-cm water tank anterior to a cadaver spine. Spiral dual-energy scans were obtained on a dual-source, 64-slice computed tomography (CT) system using a clinical protocol and automatic exposure control. Scanning was performed at two different collimations (0.6 mm and 1.2 mm) and within three phantom sizes (medium, large, and extra large) resulting in a total of six image datasets. These datasets were analyzed using the dual-energy software tool available on the CT system for both accuracy (number of stones correctly classified as either UA or non-UA) and sensitivity (for UA stones). Stone characterization was correlated with micro-CT.


RESULTS
For the medium and large phantom sizes, the DECT technique demonstrated 100% accuracy (40/40), regardless of collimation. For the extra large phantom size and the 0.6-mm collimation (resulting in the noisiest dataset), three (two cystine and one small UA) stones could not be classified (93% accuracy and 94% sensitivity). For the extra large phantom size and the 1.2-mm collimation, the dual-energy tool failed to identify two small UA stones (95% accuracy and 88% sensitivity).


CONCLUSIONS
In an anthropomorphic phantom model, dual-energy CT can accurately discriminate uric acid stones from other stone types.
Primak
Andrew N
AN
CT Clinical Innovation Center, Department of Radiology, Mayo Clinic College of Medicine, 200 First Street SW, Rochester, MN 55905, USA. primak.andrew@mayo.edu
Fletcher
Joel G
JG
Vrtiska
Terri J
TJ
Dzyubak
Oleksandr P
OP
Lieske
John C
JC
Jackson
Molly E
ME
Williams
James C
JC
McCollough
Cynthia H
CH
D015502:Absorptiometry, Photon / Q000379:methods; D000818:Animals; D002102:Cadaver; D002129:Calcium Oxalate / Q000032:analysis; D003553:Cystine / Q000032:analysis; D017886:Durapatite / Q000032:analysis; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D007669:Kidney Calculi / Q000737:chemistry* / Q000000981:diagnostic imaging; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D013552:Swine; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014527:Uric Acid / Q000032:analysis*
D002129:Calcium Oxalate; D014527:Uric Acid; D003553:Cystine; D017886:Durapatite