Acquisition of Videofluoroscopic Swallowing Studies
In a videofluoroscopy exam, the aim is to capture the highest image quality possible while being responsible about limiting unnecessary radiation exposure, however there are many factors that can influence this. Since 2007, questions regarding optimal image acquisition rate have been the focus of research conducted Professor Martin-Harris, Professor Bonilha, Professor Martino, and Professor Steele. In order to understand how technical considerations can influence the quality of data and information acquired during the videofluoroscopic swallowing assessment, it is important to understand the components involved in the generating, viewing, recording, and reviewing processes. A range of factors come into play at every stage of the exam. In fact, even when people think they are acquiring 30 frames per second, the truth is often something else altogether.
Continuous Versus Pulsed Fluoroscopy
A very important issue to understand is the difference between continuous and pulsed radiation. Historically, traditional fluoroscopy was typically continuous; meaning that when the beam was on, it produced a steady stream of radiation. New generation fluoroscopy offers an alternative, where the radiation beam can be delivered via small packets called pulses. The number of pulses that are delivered per second can be specified, and deciding on what pulse rate to use requires consideration.
Pulse Rate Versus Frame Rate
An important terminological issue to parse out is the difference between pulse rate and frame rate.
Historically, the term frame rate was used generically to describe the number of images that were generated per second in a videofluoroscopy. In the case of continuous fluoroscopy, there is no meaningful distinction between the image output rate of the fluoroscope and the rate of image display on the monitor or on the recording system. However, with pulsed radiation, the distinction becomes meaningful. When using the term pulse rate, we are referring to the output of the fluoroscope, specifically the number of bursts of radiation that are emitted per second.
When we use the term frame rate, we will be speaking more specifically about the recording end of the system, and referring to the number of images that are recorded/stored/archived per second on that system. The fact that these two things can be different introduces options that can lead to possible confusion and impact the amount of information that is available to the clinician when reviewing videofluoroscopy.
Recorded Images per Second
Historically, continuous fluoroscopy would create a continuous stream of information that was captured on the recording end as 30 images per second. With the development of pulsed fluoroscopy, the same effect (i.e., a recording containing 30 images per second) can be achieved using a pulse rate of 30 pulses per second, and a capture rate of 30 frames per second, provided that the capture system is properly synchronized with the fluoroscope. A lower pulse rate of 15 per second involves less radiation exposure than a pulse rate of 30 pulses per second, assuming a similar dose per pulse. However, if this pulsed output is recorded at a frequency of 30 frames per second, the resulting output will consist of 15 pairs of images.
There are several ways to record videofluoroscopy exams such as PACS, DVD recorders, and computers running proprietary capture software. It is also important to consider the chain of processing that the information passes through. The more links in the chain, the more susceptible the data is to being compromised, and the more settings to confirm to ensure that the quality of the final images is adequate for review. Mismatches in the rate of information being generated and being captured can result in interpolated or duplicate images in the final recorded product.
References on this topic
- Anderson, C. M. & Leidholdt, E. M. (2013). An
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- Bonilha, H. S., Blair, J., Carnes, B., Huda, W., Humphries, K., McGrattan, K., Martin-Harris, B. (2013). Preliminary investigation of the effect of pulse rate on judgments of swallowing impairment and treatment recommendations. Dysphagia, 28(4), 528-538.
- Bonilha, H. S., Humphries, K., Blair, J., Hill, E. G., McGrattan, K., Carnes, B., . . .Martin-Harris, B. (2013). Radiation exposure time during MBSS: Influence of swallowing impairment severity, medical diagnosis, clinician experience, and standardized protocol use. Dysphagia, 28(1), 77-85.
- Bronzino, J.D., ed. (2006). “Medical Devices and Systems”. The Biomedical Engineering Handbook, 4th Edition. CRC Press. Boca Raton, FL.
- Bushberg, J. T., Seibert, J.A., Leidholdt, E. M. Jr. & Boone, J. M. (2012). The Essential Physics of Medical Imaging. 3rd Edition. Lippincott Williams & Wilkin. Philadelphia, PA.
- Cohen, M. (2009). Can we use pulsed fluoroscopy to decrease the radiation dose during video fluoroscopy feeding studies in children? Clinical Radiology, 64, 70-73.
- Gingold, E. (2014). Modern Fluoroscopy Imaging Systems. Retrieved from https://www.imagewisely.org/imaging-modalities/fluoroscopy/articles/gingold-modern-systems
- Jaffer, N., Au, F. W., Ng, E. & Steele, C. M. (2015). Fluoroscopic evaluation of oropharyngeal dysphagia. AJR American Journal of Roentgenology, 204, 49-58.
- Martino, R., Shaw, S., Greco, E., Maki, E., Jabbour, N., Gomes, A.,… Ringash, J. (2015). Comparing physiological swallow measures captured on videofluoroscopy at different frame rates: A reliability analysis. Oral presentation. 22nd Dysphagia Research Society meeting. Chicago, IL.
- Nickoloff, E.L. (2011). AAPM/RSNA Physics Tutorial for Residents: Physics of Flat-Panel Fluoroscopy Systems – Survey of Modern Fluoroscopy Imaging: Flat-Panel Detectors versus Image Intensifiers and More. RSNA Radiographics, March-April, 31(2), 591-603. Retrieved from https://pubs.rsna.org/doi/10.1148/rg.312105185
- Peladeau-Pigeon, M. & Steele, C. M. (2013). Technical aspects of a videofluoroscopic swallowing study. Canadian Journal of Speech-Language Pathology and Audiology, 37(3), 216-226. Retrieved from http://www.cjslpa.ca/detail.php?ID=1130&lang=en
- Peladeau-Pigeon, M. & Steele, C. M. (2015). Understanding Image Resolution and Quality in Videofluoroscopy. Perspectives on Swallowing and Swallowing Disorders, 24(3), 115-124. Retrieved from https://sig13perspectives.pubs.asha.org/article.aspx?articleid=2395707
- Schueler, B. (2000). The AAPM/RSNA physics tutorial for residents: General overview of fluoroscopic imaging. Radiographics, 20(4), 1115-1126.