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. Author manuscript; available in PMC: 2021 Dec 1.
Published in final edited form as: Curr Opin Otolaryngol Head Neck Surg. 2020 Dec;28(6):371–375. doi: 10.1097/MOO.0000000000000665

Radiation Exposure in Modified Barium Swallow Studies

Heather Shaw Bonilha 1, Bonnie Martin-Harris 2, Ashli K O’Rourke 3, Sameer V Tipnis 4
PMCID: PMC7788513  NIHMSID: NIHMS1651396  PMID: 33027137

Abstract

Purpose of review:

The Modified Barium Swallow Study (MBSS) is an x-ray examination of swallowing used to detect the presence and type impairment, aspiration risk, and to develop intervention plans. In this review, we will cover the use of ionizing radiation in MBSSs and review recent literature concerning radiation exposure and cancer risks to patients undergoing MBSSs. Lastly, we will discuss the clinical implications of these findings.

Recent findings:

Recent literature confirms that the MBSS is a low dose exam and that reducing pulse rate negatively impacts diagnostic accuracy. Importantly, cancer risks to adults undergoing MBSSs were also reported to be low.

Summary:

An adult undergoing MBSS using a standardized, valid protocol, like the Modified Barium Swallow Impairment Profile (MBSImP), has low radiation exposure and very low associated cancer risks. MBSSs should be used when relevant to adult patient care without undue concern regarding radiation exposure. Children also have low radiation exposure from MBSSs; however, cancer risks from that exposure remain unknown. Best practices in radiation safety must always be followed. Reducing pulse rates in the adult or pediatric population to reduce radiation exposure is not a valid strategy due to the resulting reduction in diagnostic accuracy.

Keywords: deglutition, modified barium swallow study, radiation, fluoroscopy

Modified Barium Swallow Study (MBSS)

The Modified Barium Swallow Study (MBSS) is an x-ray examination that allows clinicians to visualize a patient swallowing in real time. This exam is used to identify the nature of the swallowing impairment as well as to direct the treatment approach. However, as with any x-ray exam there is radiation exposure and related risks.

Ionizing Radiation in MBSSs

Clinicians must be concerned with radiation safety for all medical uses of ionizing radiation. Although radiation exposure and related risks for adult MBSSs are low [1], it is still necessary to comply with the basic tenets of radiation safety. The As Low As Reasonably Achievable (ALARA) principle should guide procedures during MBSSs [2]. This includes only performing exams that will impact patient care; performing exams using a validated method shown to capture clinically relevant data efficiently [3], and; practicing patient and clinician safety procedures [4,5].

Radiation Exposure and Related Cancer Risks

There are two risks associated with radiation exposure: deterministic and stochastic risks [6]. Deterministic risks, such as skin burns, occur at levels of radiation exposure much higher than those used during MBSSs, and, as such, are not a concern related to the MBSS. However, there is no lower threshold for stochastic risks, indicating that all medical uses of ionizing radiation, no matter how small the radiation exposure, must have appropriate protocols and procedures to minimize risk under the ALARA principle. Stochastic risks from MBSSs are mainly the risk of cancer.

Data on radiation exposure and cancer risks of MBSS should be made available to clinicians and patients to allow them to weigh the benefit of the exam compared to the risks. Without this knowledge, some clinicians may assume cancer risks are low compared to the benefit of the diagnostic information acquired. This may result in an excessive number of repeated and/or long-duration exams. Other clinicians may assume cancer risks are high compared to the benefit of the diagnostic information acquired and rarely use MBSSs – even for initial diagnosis. Without the MBSS, patients and clinicians cannot benefit from the highly valuable clinical information afforded by the exam. And still, other clinicians are making compromises in exam quality based on assumptions that there are cancer risks but that even some low-level diagnostic information outweighs the risk. These clinicians are modifying the exam in ways to reduce the radiation exposure and associated cancer risks even though it may impact diagnostic accuracy to an unknown degree. Specifically, clinicians are stopping exams at an arbitrary time point (e.g. 1 minute) and conducting the exam with pulse rates of 15 pulses per second (pps) or lower, even though reductions in pulse rate have been shown to have a significant negative impact on diagnostic accuracy and treatment recommendations [7]. Other unvalidated clinical practices used to reduce radiation exposure from MBSSs include using intermittent sampling to visualize predefined events (5 swallows at 1.5 minutes after feeding/eating has begun) or assessing only one task during the exam (not assessing multiple bolus volumes, bolus consistencies, or interventions).

How radiation exposure and cancer risks are calculated

Radiation exposure and related cancer risks are specific to the examination and patient population. Thus, we cannot apply data or equations for other types of examinations (even other GI exams) to understand exposure and risks in MBSSs. Radiation exposure is calculated using data from the fluoroscopy unit (specifically, the quantity and quality of the x-ray beam used during the exam) combined with data on the organs imaged during the exam and patient size. Cancer risk calculations use the organ-specific radiation exposure data combined with sex and age data to determine specific risks for a given exam. Using methods common to the calculation of radiation exposure and cancer risks in other medical uses of ionizing radiation, it is possible to determine radiation exposure and related cancer risks specifically for MBSSs.

Literature review over the past 18 months (January 1, 2019 – June 31, 2020)

A literature search in PubMed, Scopus, and CINAHL using the terms (“modified barium swallow” OR fluoros* OR videofluoro*) AND (deglutition OR swallow*) AND (radiation) revealed 20 related articles in the past 18 months. There were four themes related to the topic of radiation exposure and cancer risks in MBSSs. Eight articles related directly to radiation exposure, eight articles provided an overview of the clinical use of fluoroscopy to evaluate swallowing function, three studied pulse rate, and two focused on techniques: one presented an alternative to the MBSS and another a timing protocol for specifically for infants.

Radiation Exposure

Of the eight recent articles published about radiation exposure in MBSS, 4 provided radiation dose data [8-11]. Three articles were editorials (two literature reviews [12,13] and a tutorial on imaging techniques and radiation physics) [14] and one article focused on the relationship between radiation exposure and fluoroscopy time [15].

The literature to date has verified that the MBSSs is a low dose examination with very low cancer risks in adults. One study provided data for adults, where the median dose area product (DAP) was 33.3 mGy-cm2 and the set national diagnostic reference level for Australia was 60.6 mGy-cm2 (the 3rd quartile) [8]. Doses to pediatric patients were provided in two studies with DAPs of 0.24 and 0.29 mGy-cm2 [9,10]. Cancer risk associated with the dose for adults was reported in one article as very low, the level of radiation exposure from adults undergoing MBSS has a related cancer incidence risk ranging from 0.0032% for a 20-year-old female to 0.00049% for a 60-year-old male [11].

Thus, the recent literature on the topic confirms that MBSSs in adults provide low radiation exposure associated with low cancer risks. While there is an indication that radiation exposure is also low in MBSSs in children, there is not yet information on radiation exposure when following a validated, standardized MBSS protocol or the cancer risks related to MBSSs in children. Many studies that provide effective dose values use general reference standards for organ doses that are not specific to the MBSS. This may result in misleading information.

Bonilha et al. studied the relationship between radiation dose and fluoroscopy time [15]. The results indicate that across patients radiation dose and fluoroscopy time are poorly correlated. This is because other factors (patient size, exam factors such as x-ray beam quality, collimation, etc.) influence radiation dose and are not accounted for by time alone. Thus, when evaluating across patients radiation dose is a more accurate indicator of the exam. However, within a single patient’s exam, time and radiation dose are correlated, since the patient’s size and the exam factors are held constant.

Use of MBSS

Eight articles provided editorials and practice guidelines on the use of the MBSS in adults and children [16-23] including the American College of Radiology’s appropriateness criteria statement for MBSS in patients with dysphagia [21].

Pulse Rate

Three studies investigated the influence of pulse rate on either radiation dose or diagnostic accuracy [24-26].

Galgano et al. evaluated pre- and post-changes to their MBSS procedures in their retrospective analysis of 827 patients [24]. Specifically, the pre-change MBSSs did not follow a standardized, validated protocol, such as the MBSImP, and were conducted at an extremely low pulse rate (3.75pps) in normal dose mode, while the post-change MBSSs followed the MBSImP protocol, were conducted at higher pulse rates (15pps) in low dose mode. Study results indicated a reduction in radiation exposure and fluoroscopy time in the post-change MBSSs (with a higher pulse rate and using the MBSImP protocol).

Mulheren, Azola & González-Fernández evaluated the differences in diagnostic accuracy between pulse rates of 30 and 15 in MBSSs of 20 acute stroke patients [25]. Results indicated differences between 30 and 15pps on several aspects of swallowing physiology, but differences were not found in all aspects of swallowing physiology nor in the Penetration/Aspiration Scale (PAS) score. The MBSImP components for which a difference was noted between 30 and 15pps included: oral residue, pharyngoesophageal segment opening, bolus transport, and initiation of the pharyngeal swallow. Given the components of swallowing physiology that were influenced in this preliminary study, the conclusion was that MBSSs should be conducted in continuous mode or at 30pps to optimize diagnostic accuracy.

Layly et al. described an experiment to evaluate the differences in PAS between pulse rates of 30 and 15 in swallow studies of children (4 months to 16 years) [26]. They report an ‘almost perfect’ agreement in PAS between the two pulse rates. However, 144 out of 190 (75.79%) of the swallows were normal on the PAS. Thus, there was no chance to detect a difference between 30 and 15pps in those swallows. Therefore, the statistics should have included only the 46 swallows where there was an abnormal PAS. There were 3 false positives and 3 false negatives thus in 13% (6/46) of the sample with an abnormal PAS, using 15pps impacted the judgments of PAS. Additionally, PAS is only one aspect of the MBSS; many other, shorter duration, aspects of swallowing physiology routinely evaluated during the MBSS to direct swallowing treatment were not considered. While PAS indicates the level and response of airway invasion, including aspiration, it is not a sensitive indicator of swallowing physiology. It is important to consider all the clinically-relevant information needed from a MBSS and to ensure that it is accessible at 15pps before recommending a clinical practice of using a low 15pps pulse rate. Lastly, since deleted frames were not replaced with copies of the frames during the editing to create the 15pps recordings, the recordings were shorter and thus the reviewers were not blinded to the pulse rate.

Alternative Techniques

One article described the development of an alternative to the MBSS, while the other article described the importance of capturing change over the duration of the exam in bottle-fed infants.

Arai et al. described an alternative to the MBSS with radiation reduction as the main rationale [27]. However, as detailed above, radiation exposure from MBSSs is very low and compliance with ALARA means that diagnostic accuracy should not be sacrificed. The technique used in this study employed a device to constrain movement during the swallow which would hinder the ability to test posture modifications such as chin tuck or head turn. Additionally, the results of the study are provided in a multi-color swallow chart disassociated with the anatomical image from the fluoroscopy. The study included two bolus types and did not provide information related to diagnostic accuracy, clinical utility, or radiation exposure. This was a proof-of-concept article and it will be interesting to see if it can be developed into a clinically useful tool.

McGrattan et al. described a protocol for capturing a bottle-fed infant’s swallowing function during a MBSS at specific times [28] and found that swallowing function varied during the feeding.

A Note about the use of MBSSs in Children

While the large studies are on-going, clinicians are without data to support the use or avoidance of MBSSs in children. It is common to extrapolate from the adult research; however, the adult radiation exposure and cancer risk data cannot be applied to infants or children for three main reasons: 1) children’s organs are more radiosensitive than adult organs; 2) children are smaller than adults; 3) the MBSS settings and examination protocol are different in children compared to adults.

The main organ irradiated during the MBSS is the thyroid gland. We know from BEIR VII that cancer risks related to radiation of the thyroid in a newborn male is 115 per 100,000 exposed to 100 mGy of x-rays while that of a newborn female is 634 per 100,000 exposed to 100 mGy of x-rays [29]. In comparison, the adult data show that thyroid exposure is much less likely to result in cancer (for a 50-year-old male and female the cancer risks are 1 and 4 per 100,000 exposed to 100 mGy of x-rays, respectively).

Children are smaller than adults which means that less energy is needed to create an x-ray image (the beam can more easily pass through a small child than a larger adult). Since modern fluoroscopy units are set to automatically adjust the kV and filtration to create an optimal image and not use excessive radiation, the x-ray quality (kV and filtration) is different in the MBSSs of children compared to adults. Thus, all calculations for adult studies would be inaccurate for those of children, especially very young children who are much smaller than adults.

The MBSS is typically performed differently in children than adults. While older children may be able to undergo an adult MBSS protocol, such as the MBSImP, younger children, and especially bottle-fed infants, are not. Differences in patient positioning, fluoroscopy time, patient participation, etc. will impact radiation dose and related cancer risks. Additionally, the fluoroscopy unit settings such as magnification and collimation often set differently in young children than in adults, would alter dose and risk calculations.

It is important to understand radiation dose and related cancer risks in pediatric MBSSs. This information will guide clinical practice and parent decision-making. There is an ongoing study to determine the radiation exposure and related cancer risks for infants and children which provide such data [30].

Unlike radiation exposure data, the adult pulse rate data can be applied, to some degree, to pediatric MBSSs. Recent and prior research in adults generally indicates that a reduction in pulse rate causes a reduction in diagnostic accuracy [7,25]. Since a child’s swallow is quicker than that of an adult, we can infer that the number of images available to detect a swallowing impairment is reduced by more than half in children compared to adults (0.27s vs 0.91s) [31,32]. Thus, reducing pulse rate from 30 to 15pps in children would be equivalent to performing an adult MBSS at 7.5pps (causing inaccuracies in 49.4% of scores for initiation of pharyngeal swallow). Therefore, modifying pulse rate is not an appropriate method to use to reduce radiation exposure as it is a violation of the ALARA principle (due to the large number of inaccuracies).

Conclusions

The published data reflect that the adult MBSS is a low dose examination with very low cancer risks. The MBSS should be used in adult patients with a standardized, validated protocol whenever it will impact diagnosis or treatment decision-making without undue concern for patient risks related to radiation exposure. Alternative methods of evaluation should not be used instead of a MBSS in adult patients if the sole rationale for their use is to minimize radiation exposure. Diminishing the findings from an MBSS by truncating the exam or using reduced pulse rates also should not be undertaken with a goal of radiation dose reduction. As with any examination using ionizing radiation, the principle of ALARA and radiation safety procedures must be followed. Clear information regarding cancer risks for children undergoing MBSS is not yet available; however, this research is ongoing. Calculations from adult findings on pulse rate, applied to our knowledge of the speed of a child’s swallow, allow us to infer that pulse rate reduction (anything lower than continuous or 30pps) will result in inaccurate diagnostic information.

Key Points:

  1. The adult MBSS is a low dose examination with very low cancer risks.

  2. The MBSS should not be truncated or performed with pulse rates of 15pps, or less, to reduce radiation exposure to adults as these modifications have been shown to reduce diagnostic accuracy.

  3. The cancer risks to infants and children undergoing MBSSs are not yet known; however, there is ongoing research to provide this information.

  4. Evidence indicates that the use of pulse rates of 15pps, or less, is detrimental to the diagnostic accuracy of pediatric MBSSs.

Acknowledgements

This work was supported by the National Institute of Diabetes and Digestive and Kidney Diseases Grant R01DK098222 (H. S. B., B. M. H., S. T.) and the National Institute of Diabetes and Digestive and Kidney Diseases Grant R01DK122975 (H. S. B., B. M. H., S. T.).

Footnotes

Conflicts of Interest

None.

Contributor Information

Heather Shaw Bonilha, Department of Health Science and Research, Medical University of South Carolina, Charleston, SC; Department of Otolaryngology—Head and Neck Surgery, Medical University of South Carolina, Charleston, SC.

Bonnie Martin-Harris, Roxelyn and Richard Pepper Department of Communication Sciences and Disorders, Northwestern University, Evanston, IL.

Ashli K. O’Rourke, Department of Otolaryngology—Head and Neck Surgery, Medical University of South Carolina, Charleston, SC.

Sameer V. Tipnis, Department of Radiology and Radiological Science, Medical University of South Carolina, Charleston, SC

References:

  • 1.Bonilha HS, Wilmskoetter J, Martin-Harris B, Tipnis SV, Huda W. Effective dose per unit kerma area product conversion factors in adults undergoing Modified Barium Swallow Studies. Radiation Protection Dosimetry 2017; 176(3):269–277. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 2.ALARA - U.S. Nuclear Regulatory Commission. Title 10, Section 20.1003, of the Code of Federal Regulations (10 CFR 20.1003) https://www.nrc.gov/reading-rm/basic-ref/glossary/alara.html
  • 3.Bonilha HS, Humphries K, Blair J, Hill E, McGrattan K, Carnes B, Huda W, Martin-Harris B. Radiation exposure time during MBSS: Influence of swallowing impairment severity, medical diagnosis, clinician experience, and standardized protocol use. Dysphagia 2013; 28(1):77–85. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 4.Kelchner L Radiation Safety During the Videofluoroscopic Swallow Study. Perspectives on Swallowing and Swallowing Disorders 2004. [Google Scholar]
  • 5.Hayes A et al. Radiation safety for the speech-language pathologist. Dysphagia 2009; 24:274–279. [DOI] [PubMed] [Google Scholar]
  • 6.Bushberg JT, Seibert JA, Leidholdt EM Jr., Boone JM. The Essential Physics of Medical Imaging, Third Edition (Third, North American: edition). Lippincott, Williams & Wilkins; 2012. [Google Scholar]
  • 7.Bonilha HS, Blair J, Carnes B, Huda W, McGrattan K, Humphries K, Michaels Y, Martin-Harris B. Preliminary investigation of the effect of pulse rate on judgments of swallowing impairment and treatment recommendations. Dysphagia 2013; 28(4):528–538. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 8. *.Wachabauer D, Röthlin F, Moshammer HM, Homolka P. Diagnostic Reference Levels for conventional radiography and fluoroscopy in Austria: Results and updated National Diagnostic Reference Levels derived from a nationwide survey. Eur J Radiol 2019; 113:135–139.This article provides national diagnostic reference levels for MBSSs in Austria.
  • 9.Ko EJ, Sung IY, Choi KH, Kwon YG, Yoon J, Kim T. Radiation exposure during videofluoroscopic swallowing studies in young children. Int J Pediatr Otorhinolaryngol 2019; 121:1–5. [DOI] [PubMed] [Google Scholar]
  • 10.Im HW, Kim SY, Oh BM, Han TR, Seo HG. Radiation dose during videofluoroscopic swallowing studies and associated factors in pediatric patients. Dysphagia 2020; 35(1):84–89. [DOI] [PubMed] [Google Scholar]
  • 11. **.Bonilha HS, Huda W, Wilmskoetter J, Martin-Harris B, Tipnis SV. Radiation Risks to Adult Patients Undergoing Modified Barium Swallow Studies. Dysphagia 2019; 34(6):922–929.This article provides the cancer risks for adults undergoing MBSSs.
  • 12.Earl VJ, Badawy MK. Radiation exposure to staff and patient during videofluoroscopic swallowing studies and recommended protection strategies. Dysphagia 2019; 34(3):290–297. [DOI] [PubMed] [Google Scholar]
  • 13.Hong JY, Hwang NK, Lee G, Park JS, Jung YJ. Radiation safety in videofluoroscopic swallowing study: systematic review [published online ahead of print, 2020 April 11]. Dysphagia 2020; 10.1007/s00455-020-10112-3. [DOI] [Google Scholar]
  • 14.Ekberg O. (2004) Imaging Techniques and Some Principles of Interpretation (Including Radiation Physics) In: Ekberg O. (eds) Radiology of the Pharynx and the Esophagus. Medical Radiology (Diagnostic Imaging). Springer, Berlin, Heidelberg: 10.1007/978-3-642-18838-1_3 [DOI] [Google Scholar]
  • 15. *.Bonilha HS, Wilmskoetter J, Tipnis S, Horn J, Martin-Harris B, Huda W. Relationships Between Radiation Exposure Dose, Time, and Projection in Videofluoroscopic Swallowing Studies. Am J Speech Lang Pathol 2019; 28(3):1053–1059.Results indicate that radiation dose and not fluoroscopy time should be used when comparing radiation exposure across patients.
  • 16.Batchelor G, McNaughten B, Bourke T, Dick J, Leonard C, Thompson A. How to use the videofluoroscopy swallow study in paediatric practice. Arch Dis Child Educ Pract Ed 2019; 104(6):313–320. [DOI] [PubMed] [Google Scholar]
  • 17.Benfield JK, Michou E, Everton LF, et al. The Landscape of Videofluoroscopy in the UK: A Web-Based Survey [published online ahead of print, 2020 May 16]. Dysphagia 2020; 10.1007/s00455-020-10130-1. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 18.Boaden E, Nightingale J, Bradbury C, Hives L, Georgiou R. Clinical practice guidelines for videofluoroscopic swallowing studies: A systematic review. Radiography (Lond) 2020; 26(2):154–162. [DOI] [PubMed] [Google Scholar]
  • 19.Bülow M The therapeutic swallowing study. Med Radiol 2019; 565–580. [Google Scholar]
  • 20.Fynes MM, Smith C, Brodsky MB. The modified barium swallow study: When, how, and why? Appl Radiol 2019; 48(5):3–8. [Google Scholar]
  • 21. *.Levy AD, Carucci LR, Bartel TB, et al. Expert Panel on Gastrointestinal Imaging: ACR Appropriateness Criteria® Dysphagia. J Am Coll Radiol 2019; 16(5S):S104–S115.This editorial details the guidelines from the American College of Radiology for using MBSSs to evaluate swallow function.
  • 22.Lo Re G, Vernuccio F, Di Vittorio ML, et al. Swallowing evaluation with videofluoroscopy in the paediatric population. Acta Otorhinolaryngol Ital 2019; 39(5):279–288. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 23.Regan J, Wiesinger T, Keane J, Walshe M. Oesophageal screening during videofluoroscopy: International practices and perspectives of speech-language pathologists [published online ahead of print, 2020 February 13]. Int J Speech Lang Pathol 2020; 1–10. [DOI] [PubMed] [Google Scholar]
  • 24. **.Galgano SJ, Gauntt D, Boyd MR, et al. Trade-off between pulse rate and radiation dose during modified barium swallow examination: what is the reality? Clin Radiol 2019; 74(9):736.e9–736.e12.Demonstrated the ability to increase pulse rate without increasing radiation exposure.
  • 25. **.Mulheren RW, Azola A, González-Fernández M. Do Ratings of Swallowing Function Differ by Videofluoroscopic Rate? An Exploratory Analysis in Patients After Acute Stroke. Arch Phys Med Rehabil 2019; 100(6):1085–1090.Results indicate that reducing pulse rate from 30 to 15pps reduces diagnostic accuracy in adult MBSSs.
  • 26.Layly J, Marmouset F, Chassagnon G, et al. Can We Reduce Frame Rate to 15 Images per Second in Pediatric Videofluoroscopic Swallow Studies?. Dysphagia 2020; 35(2):296–300. [DOI] [PubMed] [Google Scholar]
  • 27.Arai N, Hanayama K, Yamazaki T, Tomita T, Tsubahara A, Sugamoto K. A novel fluoroscopic method for multidimensional evaluation of swallowing function. Auris Nasus Larynx 2019; 46(1):83–88. [DOI] [PubMed] [Google Scholar]
  • 28.McGrattan KE, McGhee HC, McKelvey KL, et al. Capturing infant swallow impairment on videofluoroscopy: timing matters. Pediatr Radiol 2020; 50(2):199–206. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 29.National Research Council of the National Academies Health risks from exposure to low levels of ionizing radiation: BEIR VII Phase 2. Washington: The National Academies Press; 2006. p.245. [Google Scholar]
  • 30.Bonilha HS, Tipnis S, Martin-Harris B, Lefton-Grief M, Nietert P. R01DK122975 NIH/NIDDK: Excess Radiation Exposure in Infants and Children from Videofluoroscopic Swallow Studies. 2020https://projectreporter.nih.gov/project_info_description.cfm?aid=9858922&icde=50339485&ddparam=&ddvalue=&ddsub=&cr=1&csb=default&cs=ASC&pball=
  • 31.Gosa MM, Suiter DM, Kahane JC. Reliability for identification of a select set of temporal and physiologic features of infant swallows. Dysphagia 2015; 30:365–372. [DOI] [PubMed] [Google Scholar]
  • 32.Kendall KA, McKenzie S, Leonard RJ, Gonçalves MI, Walker A. Timing of events in normal swallowing: a videofluoroscopic study. Dysphagia 2000; 15:74–83. [DOI] [PubMed] [Google Scholar]

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