The advantages of an attenuated total internal reflection infrared microspectroscopic imaging approach for kidney biopsy analysis.

The benefits of an attenuated total reflection Fourier transform infrared (ATR-FTIR) imaging approach for kidney biopsy analysis are described. Biopsy sections collected from kidney-stone formers are analyzed at the initial stages of stone development to provide insights into stone growth and formation. The majority of tissue analysis currently conducted with IR microspectroscopy is performed with a transflection method. The research presented in this manuscript demonstrates that ATR overcomes many of the disadvantages of transflection or transmission measurements for tissue analysis including an elimination of spectral artifacts. When kidney biopsies with small mineral inclusions are analyzed with a transflection approach, specular reflection and the Christiansen effect (anomalous dispersion) can occur, leading to spectral artifacts. Another effect specific to the analysis of mineral inclusions present in kidney biopsies is known as the reststrahlen effect whereby the inclusions become strong reflectors near an absorption band. ATR eliminates these effects by immersing the sample in a high index medium. Additionally, the focused beam size for ATR is decreased by a factor of four when a germanium internal reflection element is used, 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 quantification.

Attenuated total internal reflection Fourier transform infrared spectroscopy: a quantitative approach for kidney stone analysis.

The impact of kidney stone disease is significant worldwide, yet methods for quantifying stone components remain limited. A new approach requiring minimal sample preparation for the quantitative analysis of kidney stone components has been investigated utilizing attenuated total internal reflection Fourier transform infrared spectroscopy (ATR-FT-IR). Calcium oxalate monohydrate (COM) and hydroxylapatite (HAP), two of the most common constituents of urinary stones, were used for quantitative analysis. Calibration curves were constructed using integrated band intensities of four infrared absorptions versus concentration (weight %). The correlation coefficients of the calibration curves range from 0.997 to 0.93. The limits of detection range from 0.07 +/- 0.02% COM/HAP where COM is the analyte and HAP is the matrix, to 0.26 +/- 0.07% HAP/COM where HAP is the analyte and COM is the matrix. This study shows that linear calibration curves can be generated for the quantitative analysis of stone mixtures provided the system is well understood especially with respect to particle size.