Laser blood test takes clinical data

28 Nov 2002

A five-minute test uses Raman spectroscopy to measure levels of nine crucial components in blood.

Medical diagnosis could be aided by a simple blood test based on Raman spectroscopy developed by Michael Feld and colleagues at Massachusetts Institute of Technology (MIT).

The test can identify the concentration of nine components in a blood sample. It is believed to be the first time that a single technique has quantitatively measured such a large number of compounds simultaneously in whole blood (Optics Letters 27 2004).

Feld's team carried out the test, which takes approximately five minutes to perform, on 31 patients in a Boston hospital.

Concentrations of glucose, urea, total protein, cholesterol, albumin, bilirubin, triglycerides, hematocrit and hemoglobin were measured in the test. Of these compounds, all but bilirubin and cholesterol could be detected with a precision good enough for clinical use.

The technique uses a Raman spectrometer based around an 830 nm diode laser source, but the MIT team found that the turbidity of blood caused scattering patterns that could not be collected efficiently using conventional optics.

After optimizing the collection optics using a design code from US company Zemax, they introduced a gold-coated, half-paraboloid mirror into the setup.

According to the researchers, this 15.9 mm focal-length mirror collects about 25 % of the total Raman-scattered light from the blood - making it around four times more efficient than conventional lenses used in a previous system.

In the test, 30 consecutive spectra of each sample were taken over five minutes, with conventional clinical methods used to calibrate the Raman test. A CCD detector captured scattered light in the range 650-1650 cm^-1, which contained the necessary spectral information to determine each concentration.

Feld and colleagues say that the work demonstrates that the technique is suitable for clinical use.

Author
Michael Hatcher is technology editor of Opto and Laser Europe magazine.