Comparison of absorption measurements of DNA stain content by utilizing video and scanning image cytometers

After staining with the Feulgen reaction, the DNA stain contents of 155 mouse bone marrow cells and 22 adjacent chicken erythrocytes were measured by absorption image cytometry by utilizing two different systems--a scanning cytometer and a video cytometer. In the scanning cytometer (M85 microdensitometer, Vickers Instruments, Malden, MA), a spot of light was scanned across the cell. In the video cytometer (TAS Plus, E. Leitz, Rockleigh, NJ), the microscope field, which may contain several nuclei, was imaged onto a Plumbicon video camera. With each system, cells were scanned, digitized into their elementary pixels, and analyzed to determine their integrated absorbance. Comparison of the DNA stain contents of the same G0/G1 bone marrow cells and chicken erythrocytes, as measured by video and scanning cytometry, showed that both techniques gave comparable results; scanning cytometry is more precise. The coefficients of variation of the measurements for the G0/G1 bone marrow cells and for the chicken erythrocytes were 5.9% and 7.0%, respectively, when measured by video cytometry at the absorption peak (584 nm), compared to 4.1% and 3.5%, respectively, for the same cells when measured by scanning cytometry off the absorption peak (615 nm). The video-based measurements were relatively lower than the scanning measurements for darkly stained cells; this suggests that glare and other optical errors which increase with stain darkness caused greater systematic errors in the video cytometer than they did in the scanning cytometer.