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.
CT Clinical Innovation Center, Department of Radiology, Mayo Clinic College of Medicine, 200 First Street SW, Rochester, MN 55905, USA. primak.andrew@mayo.edu
Andrew N
AN
Primak
Joel G
JG
Fletcher
Terri J
TJ
Vrtiska
Oleksandr P
OP
Dzyubak
John C
JC
Lieske
Molly E
ME
Jackson
James C
JC
Williams
Cynthia H
CH
McCollough
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