Hemoglobin Absorption Spectral Imaging (H.A.S.I.): a novel optical staining technique for microlaryngoscopy

Optical image enhancement techniques are widely used in endoscopy to improve the visualization of blood vessels for diagnostic and therapeutic purposes. These techniques are monitor-based and therefore not available for direct microscopy. In this study, a novel optical microscope filter, Hemoglobin absorption spectral imaging (H.A.S.I.) was tested for use in microlaryngoscopy.

A novel dichroic filter was designed to improve contrast in small blood vessels by highlighting transmission in the spectrum range of hemoglobin absorption maxima. A surgical microscope equipped with the novel H.A.S.I. filter was installed in one operating room in our institution. 68 consecutive patients referred to our ENT department for endoscopy were examined using white light and the novel H.A.S.I. filter during microlaryngoscopy. Surgeons described the blood vessels of the vocal cords using a classification chart and assessed for suspected malignancy using both white light and H.A.S.I.

77 consecutive microlaryngoscopies were performed on 68 patients. 142 vocal cords were visualized in microlaryngoscopy and the blood vessels classified according to the chart. With white light, 152 blood vessel characteristics were documented and 157 with H.A.S.I. Notably, pathologies like benign horizontal blood vessel changes, leukoplakia, and vertical blood vessel changes like dots and loops were seen more frequently with H.A.S.I. Finally, seven lesions were treated by transoral laser microsurgery (TLM) with H.A.S.I. to test the practicability of the method for microlaryngoscopic laser surgery.

This is the first study describing H.A.S.I. as an optical staining method for microlaryngoscopy. In our experience, the method was practical and improved the evaluation of vocal cord blood vessels. In some cases, the use of H.A.S.I. led to a change in diagnosis and treatment. Also, H.A.S.I. was found to be helpful in microlaryngeal laser surgery for demarcating resection margins. This is, to our knowledge, the first optical staining method integrated into a surgical microscope and can be conveniently used during microlaryngeal laser surgery and does not require further equipment.