UROLOGY: ATR-FTIR gets to the core of kidney-stone development

Learning the cause of initial kidney-stone formation–a poorly understood process–requires the study of small mineral inclusions in tissue biopsies,1 says Heather J. Gulley-Stahl, a graduate student under the direction of Dr. Andre Sommer at Miami University (Oxford, OH), who presented her work during Pittcon 2009.

Traditionally, this type of analysis has relied on histological preparations and examination with an optical microscope–an approach imposing numerous time and process limitations. According to Gulley-Stahl, infrared methods can yield similar information–and also provide the molecular information required for proper disease detection.


A white-light microscope image shows 30 to 40 µm calcium oxalate mineral inclusions (left). The same tissue looks blurry when imaged using R/A, because of limited spatial resolution (center). But an ATR image of the same location enables effortless viewing of mineral inclusions, thanks to increased spatial resolution (right).
Click here to enlarge image

Collaborating with Dr. Andrew Evan, director of the International Kidney Stone Institute at Indiana University Medical School, Gulley-Stahl collected biopsy sections from idiopathic calcium stone formers and analyzed them at the initial stages of stone development.2 “Currently, the majority of tissue analysis with IR microscopy is conducted with a reflection/absorption method, which is hampered by specular reflection artifacts and a spatial resolution of 4λ at best,” she reports. She adds that discontinuities within tissue samples–such as blood vessels and mineral inclusions–can present high contrast edges, which promotes scattering, diffraction, reflection and dispersion and produces numerous problems.3

Her research demonstrates that attenuated total reflectance (ATR) overcomes many of the disadvantages of transmission or reflection/absorption measurements for tissue analysis, including elimination of specular artifacts. For instance, analyzing kidney biopsies with a reflection/absorption approach can produce the Restrahlen effect when small mineral inclusions surrounded by tissue become perfect reflectors near an absorption band. “ATR eliminates the Restrahlen effect,” Gulley-Stahl says, “by immersing the sample in a high-index medium.” Also, she says, the spatial resolution for ATR is increased to approximately 1λ, allowing the acquisition of spectra from small mineral inclusions several micrometers in diameter. If quantitative analysis of small mineral inclusions is ultimately desired, ATR provides the photometrically accurate spectra necessary for quantitation.

“Ultimately, we would like to be able to quantitatively analyze small mineral inclusions that have a mixed composition at the very initial stages of stone formation,” says Gulley-Stahl. “This information could potentially allow a better understanding of initial stone formation and provide clues to aid in determining a cure for kidney stone disease.”–Barbara G. Goode

REFERENCES

  1. R. L. Ryall, Urol. Res. 36, 77 (2008).
  2. A. P. Evan et al., Anat. Rec. 290, 1315 (2007).
  3. M. Romeo and M. Diem, Vibrational Spectroscopy 38, 129 (2005).

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