Medical video recording

Part IV: High-speed camera

Changes in the philosophy of recording slow-motion sequences

Author: MSc Anna Racino, Ph.D. Marcin Just, Ph.D. Michał Tyc (DiagNova Technologies)
Date: 2019.07.01

In the above-described high-speed cameras available before 2018, due to hardware limitations related to the protection of light transmitting elements and consisting in a short time of permissible operation of the lighting (usually a few seconds), it was not possible to insert the endoscope in a fully controlled manner so as to obtain the visibility of the vocal folds.In order to take full advantage of all the light, the image recording was started when the light was turned on and one long sequence lasting several seconds was recorded. The sequence was saved in the memory of the camera head and only after one examination with one recording was completed, the data was transferred to the computer in its entirety. Note that 4 seconds of recording at 2,000 fps equals 8,000 frames. With the preview at 16 fps, viewing the entire material takes almost 10 minutes of observation. With such a long period of time, it is easy to lose concentration and overlook important elements. Generating kymographic sections was a great help, but still the analysis of the record took several minutes, making the study difficult to perform in a clinical setting.

A different rule was adopted for the set Advanced Larynx Imager: ALI Cam HS1 + ALI Lum + DiagnoScope Specialist. Thanks to the laser illuminator, it was possible to control the light in such a way as to obtain a preview of the image from the camera at a significantly reduced light intensity. This made it possible to introduce a method of working rather characteristic for stroboscopy - the controlled insertion of the endoscope and obtaining the vocal folds image preview, and then recording individual short (~ 100 ms) sequences in the high-speed video mode at phonation moments. This made the examination even simpler than in the case of stroboscopy, because there is no need to wait for the synchronization of stroboscopy with the patient's voice - the slow-motion sequence can be recorded at any time, with 200 sequences recorded by default frames with the possibility of switching to the mode with sequences up to 2000 frames, when it is necessary to register the beginning or end of phonation, or transient phenomena. In the first case (200 frames), the amount of data is only several times higher than the amount of data from the strobe recording, and the entire analysis is essentially the same, taking into account the lack of the need for additional stabilization of the image from the high-speed camera, unlike the strobe image, and with the possibility of obtaining kymographic sections immediately.

    In the latest version, the DiagnoScope interface for high-speed camera (Fig. 22) is therefore equipped with 4 operating modes:
  1. HD recording,
  2. „high speed” recordings in a simplified 1/10 s mode, ensuring the greatest ease of processing and analysis, and operation slightly similar to stroboscopy,
  3. „high speed”recordings in one-second recording mode, providing more data and the ability to perform multi-period analyzes including jitter and shimmer,
  4. recordings in EVI mode using violet light.

Fig. 22. DiagnoScope data logging window with improved control and new operating modes

In all modes, the recordings are now made in a way that allows for the highest image quality and, additionally, its subsequent correction. Additionally, thanks to the autofocus and digital control of the camera lens parameters, a mechanism has been introduced that allows for much more accurate - than in the case of classic endoscopic equipment - determining the size of structures in the images (Fig. 23).

Fig. 23. New – thanks to digital control of the lens parameters, the process of determining the size of structures in the pictures has been significantly simplified and its accuracy has increased