Helical computed tomography accurately reports urinary stone composition using attenuation values: in vitro verification using high-resolution micro-computed tomography calibrated to fourier transform infrared microspectroscopy.
OBJECTIVE
To assess the ability of helical computed tomography (CT) to differentiate regions of known mineral composition in typical, heterogeneous urinary stones. Interest is substantial in the urologic community in using radiologic imaging to determine accurately the composition of urinary calculi. Recent advances in CT make this a viable prospect, but the heterogeneity of most stones is a complicating factor.


METHODS
The ability of micro-CT (a high-resolution laboratory instrument) to identify the mineral composition of stones was confirmed by calibrating micro-CT attenuation values to pure mineral regions of sliced stones using infrared microspectroscopy. Intact human urinary stones were then analyzed by micro-CT, and regions-of-interest of pure mineral were correlated with identical regions-of-interest from quad slice multi-detector row helical CT images. With helical CT, narrow slice widths were used to decrease volume-averaging errors, and bone windows were used so that internal stone structure was visible.


RESULTS
When stones were imaged using helical CT at narrow slice widths, mineral-specific regions-of-interest yielded nonoverlapping attenuation values for uric acid (566 to 632 Hounsfield units [HU]), struvite (862 to 944 HU), calcium oxalate (1416 to 1938 HU), and hydroxyapatite (2150 to 2461 HU).


CONCLUSIONS
High resolution helical CT yields unique attenuation values for common types of stone mineral, but proper windowing is required to localize regions of homogeneity. The results of this in vitro study suggest that high-resolution helical CT may be able to identify stone composition at patient diagnosis.
Zarse
Chad A
CA
Department of Anatomy and Cell Biology, Indiana University School of Medicine, Indianapolis, Indiana 46202-5120, USA.
McAteer
James A
JA
Tann
Mark
M
Sommer
Andre J
AJ
Kim
Samuel C
SC
Paterson
Ryan F
RF
Hatt
Erin K
EK
Lingeman
James E
JE
Evan
Andrew P
AP
Williams
James C
JC
D002129:Calcium Oxalate / Q000032:analysis*; D002138:Calibration; D017886:Durapatite / Q000032:analysis*; D005240:Feasibility Studies; D006801:Humans; D008096:Lithotripsy; D036542:Tomography, Spiral Computed / Q000379:methods*; D014527:Uric Acid / Q000032:analysis*; D014545:Urinary Calculi / Q000737:chemistry* / Q000000981:diagnostic imaging*
D002129:Calcium Oxalate; D014527:Uric Acid; D017886:Durapatite