Editors' ChoiceBiomedical Imaging

Leave No Stone Unturned

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Science Translational Medicine  15 Jun 2011:
Vol. 3, Issue 87, pp. 87ec92
DOI: 10.1126/scitranslmed.3002754

Using hyperspectral imaging cameras, scientists can remotely study planet geochemistry. Closer to home, scientists can use multispectral imaging to sense chemicals inside the human body. A recent study by Qu et al. demonstrates how computed tomography (CT) can be used to noninvasively image kidney stones, which allows the clinician to determine chemical makeup and thus provide better treatment. For example, stones containing cystine or calcium oxalate are hard, and treating with shockwaves might not be effective; instead, these stones might require surgical removal. In contrast, uric acid stones may be broken up by simply shifting the pH of the urine via medication.

Qu and colleagues introduce a novel dual-energy CT (DE-CT) technique—with a twist—to perform such imaging in vivo. DE-CT uses x-rays of two different energy spectra, each of which is attenuated differently by the same stone. Using micro-CT analysis and Fourier transform infrared spectroscopy, the authors first separated 43 different human kidney stones into 10 different categories. The major division was between uric acid and non–uric acid stones, with non–uric acid stones further divided into four subcategories. The stones were then placed in pig kidneys ex vivo, immersed in a CT “phantom” (a structure simulating the human abdomen), and then scanned with DE-CT. The ratios of low-energy to high-energy x-ray attenuation measures were obtained to discern uric acid from non–uric acid stones. The authors also imaged the stones with a tin filter at the higher energy level. The presence of the filter decreased the overlap between the low- and high-energy spectra and increased the CT number ratios, which improved substantially the identification of non–uric acid stone types.

Although improved subclassification of kidney stones is now possible with DE-CT, it requires slightly more radiation than single-energy CT. When compared with surgical alternatives, this increased radiation dose with advanced chemical imaging techniques might be a much smaller price to pay for diagnosing and treating those painful kidney stones.

M. Qu et al., Dual-energy dual-source CT with additional spectral filtration can improve the differentiation of non–uric acid renal stones: An ex vivo phantom study. Am. J. Roentgenol. 196, 1279–1287 (2011). [Abstract]

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