a good understanding of the details of tongue movement is critical for the diagnosis and treatment of such conditions . during swallowing ,
many methods have been employed to track these movements , including videofluoroscopy [ 13 ] , electromyography [ 46 ] , electro - magnetic articulography , palatography , magnetic resonance imaging , scintigraphy , and tongue pressure measurements . among these methods
, videofluoroscopy is considered the criterion standard for deglutition and dysphagia evaluation [ 1215 ] .
this method records the movement of radiopaque barium through the upper digestive tract in real time using conventional x - rays .
however , because of the risks of radiation exposure , repeated fluoroscopic evaluations are often avoided .
real - time ultrasound is a non - ionizing imaging modality and has been used to observe deglutitive movements since the late 1970s [ 1620 ] .
qualitative differences have been observed between patients with dysphagia and normal subjects in b - mode images , and the capability of ultrasonography for detailed , repeatable , and dynamic soft tissue imaging makes it superior to videofluoroscopy for deglutitive tongue research .
moreover , ultrasonography has higher sensitivity for assessing the dynamic factors that represent the early signs of dysphagia , such as reduced or disorganized tongue movement and fragmented swallowing .
methodological innovations and technological advances have advanced ultrasonography from qualitative observations to quantitative assessments of the dynamic aspects of swallowing . by imaging lingual contour changes ,
temporal and spatial measurements can be made during swallowing in different imaging planes . to improve ultrasound imaging stability , peng et al .  
developed the cushion scanning technique , which replaced the traditional hand - held transducer - skin coupling method , to minimize probe movement and inadvertent submental compression .
b+m - mode ultrasonography was also used to assess lingual propulsion during oral bolus transport . with this technique ,
m - mode traces represent the sequential movements of the tongue dorsum during swallowing , from which quantitative measurements could be made .
although combined b+m mode ultrasonography has been widely used in assessing deglutitive tongue movements , no conclusive results have been obtained thus far [ 2628 ] .
for example , galen et al .   reported that none of the subjects examined by real - time b+m - mode ultrasonography showed a clearly reproducible trace .
for deglutitive ultrasound to reach clinical utility , it is necessary to determine a common feature in the m - mode traces as a reference , particularly to enable accurate inter - subject comparisons .
for example , in deglutitive videofluoroscopy , a common measurement for image - based displacement is the subject - specific distance from the anterior - inferior corner of one cervical vertebra to that of another .
divided the swallowing process into 5 phases ( phases i , iia , iib , iiia , and iiib ) based on specific inflection points identified on the m - mode traces , which is used to determine and interpret variations within each swallowing phase of the trace sequence .
it also has been shown that tongue movements during swallowing have age - related changes . in this study , we used b+m mode ultrasonography to observe the tongue movements during swallowing in normal adults of different age groups .
we recorded the swallow - related activity types of each phase to determine a common feature as measurement reference in the m - mode traces and to establish reference measurements for data normalization .
the exclusion criteria were : ( 1 ) congenital malformation of oral cavity , ( 2 ) history of oral or orthodontic surgery , and ( 3 ) disease processes that may cause deglutition disorders , such as dysphagia .
the participants were divided into 3 age groups  2039 years , 4059 years , and 6080 years  with 15 males and 15 females in each age group .
this observational study was approved by the ethics committee of chinese pla general hospital , and written informed consent was obtained from all subjects .
a philips iu22 ( philips medical systems , bothell , wa ) ultrasound machine equipped with a c5 - 2 convex transducer was used .
the transducer was placed submentally in the midsagittal plane , centered between the anterior border of the hyoid bone and the posterior border of the mandibular symphysis , with the central sound wave running perpendicular to the frankfort horizontal plane .
subjects were examined in the upright position with the head and transducer fixed by a special device to avoid relative movements between them ( figure 1 ) .
the m - mode scanning section was set at the mid - portion of the tongue at a distance of 34 cm from the symphysis .
with the subject s head kept in neutral position , the subject was asked to perform a saliva swallow 30 s after drinking 35 ml of mineral water .
three saliva swallows were recorded for each participant . the latex bag filled with water , the  cushion technique ,  as described by peng et al .
spss version 13.0 ( spss inc . ; chicago , il ) was used for statistical analysis .
an analysis of variance ( anova ) test was used for the comparison of variables in the m - mode images among the 3 age groups .
the exclusion criteria were : ( 1 ) congenital malformation of oral cavity , ( 2 ) history of oral or orthodontic surgery , and ( 3 ) disease processes that may cause deglutition disorders , such as dysphagia .
the participants were divided into 3 age groups  2039 years , 4059 years , and 6080 years  with 15 males and 15 females in each age group .
this observational study was approved by the ethics committee of chinese pla general hospital , and written informed consent was obtained from all subjects .
a philips iu22 ( philips medical systems , bothell , wa ) ultrasound machine equipped with a c5 - 2 convex transducer was used .
the transducer was placed submentally in the midsagittal plane , centered between the anterior border of the hyoid bone and the posterior border of the mandibular symphysis , with the central sound wave running perpendicular to the frankfort horizontal plane .
subjects were examined in the upright position with the head and transducer fixed by a special device to avoid relative movements between them ( figure 1 ) .
the m - mode scanning section was set at the mid - portion of the tongue at a distance of 34 cm from the symphysis .
with the subject s head kept in neutral position , the subject was asked to perform a saliva swallow 30 s after drinking 35 ml of mineral water .
three saliva swallows were recorded for each participant . the latex bag filled with water , the  cushion technique ,  as described by peng et al . , was not used .
spss version 13.0 ( spss inc . ; chicago , il ) was used for statistical analysis .
an analysis of variance ( anova ) test was used for the comparison of variables in the m - mode images among the 3 age groups .
in the m - mode images , the tongue was characterized by a hyperechoic line that synchronized with the movements of tongue during swallowing ( figure 2 ) .
both intra - individual and inter - individual differences during the 3 saliva swallows of each subject were examined .
although the amplitude and duration of the m - mode traces differed , characteristic types could be identified during the following individual swallowing phases : type 1 . prior to swallow initiation , the tongue tip contacted the maxillary teeth or the incisive papilla , and the posterior portion of the tongue was raised cranially . during swallow initiation , the central part of the tongue moved with a caudal concavity that appeared as a downward slope in the m - mode tracing .
both the anterior and mid - portions of the tongue remained in contact with the hard palate .
the m - mode images demonstrated an easily identifiable hyperechoic horizontal line formed by the contraction of the tongue muscles ( figure 3 ) .
the mid - portion of the tongue moved upwards to contact the palate in this phase . an upward slope in m - mode traces
was found in every subject , and no variations were detected ( figure 4 ) .
the mid - portion of the tongue remained in contact with the palate , which was represented by a horizontal trace in m - mode images .
compressive peristaltic waves of the tongue surface producing an inverted  v  trace ( a downward slope followed by an upward slope ) in the m - mode images .
the mid - portion of the tongue moved downwards then upwards to return to the state of rest at the end of the oral swallowing process . in the m - mode images ,
a downward slope was recorded in phase iiia and was always followed by an upward trace in phase iiib , which appeared as a  u  or 
the mid - portion of the tongue returned to the rest state . in the m - mode images ,
phase iiia revealed a downward trace that was then followed by a horizontal line during phase iiib .
the tongue dorsum remained on the palate after swallowing . in the m - mode images ,
table 2 shows the ratio of each phase subtype during different swallowing phases . in phase
i , the frequency of type 1 was much higher than type 2 . in phase iib ,
type 2 was more frequent than type 1 , because the mid - portion of the tongue typically dipped instead of remaining in contact with the palate . in phase iii ,
all subjects displayed a continuous upward trace in m - mode images of phase iia during 3 saliva swallows .
for this reason , spatial and temporal measurements of phase iia were made from the m - mode images .
the swallow - related radial displacement of the mid - tongue surface during phase iia was measured , as well as the duration of tongue movement ( figure 7 ) .
figure 8 shows the average swallow - related radial displacement of the mid - tongue surface during phase iia .
the average displacement gradually decreased with age in both females and males , but these trends did not reach statistical significance among the 3 age groups ( p=0.116 and p=0.726 , respectively ) .
however , males demonstrated a significantly greater degree of displacement than females across all age groups ( p=0.002 , p<0.001 , and p<0.001 , respectively ) .
the average duration during phase iia gradually increased with age in both females and males , although these trends did not reach statistical significance among the 3 age groups ( p=0.284 and p=0.237 , respectively ) .
however , males had a significantly longer swallowing duration than females across all age groups ( p<0.001 , p<0.001 , and p<0.001 , respectively ) .
in the m - mode images , the tongue was characterized by a hyperechoic line that synchronized with the movements of tongue during swallowing ( figure 2 ) .
both intra - individual and inter - individual differences during the 3 saliva swallows of each subject were examined .
although the amplitude and duration of the m - mode traces differed , characteristic types could be identified during the following individual swallowing phases : type 1 . prior to swallow initiation , the tongue tip contacted the maxillary teeth or the incisive papilla , and the posterior portion of the tongue was raised cranially . during swallow initiation , the central part of the tongue moved with a caudal concavity that appeared as a downward slope in the m - mode tracing .
both the anterior and mid - portions of the tongue remained in contact with the hard palate .
the m - mode images demonstrated an easily identifiable hyperechoic horizontal line formed by the contraction of the tongue muscles ( figure 3 ) .
the mid - portion of the tongue moved upwards to contact the palate in this phase . an upward slope in m - mode traces
was found in every subject , and no variations were detected ( figure 4 ) .
the mid - portion of the tongue remained in contact with the palate , which was represented by a horizontal trace in m - mode images .
compressive peristaltic waves of the tongue surface producing an inverted  v  trace ( a downward slope followed by an upward slope ) in the m - mode images .
the mid - portion of the tongue moved downwards then upwards to return to the state of rest at the end of the oral swallowing process . in the m - mode images ,
a downward slope was recorded in phase iiia and was always followed by an upward trace in phase iiib , which appeared as a  u  or 
the mid - portion of the tongue returned to the rest state . in the m - mode images ,
phase iiia revealed a downward trace that was then followed by a horizontal line during phase iiib .
the tongue dorsum remained on the palate after swallowing . in the m - mode images ,
table 2 shows the ratio of each phase subtype during different swallowing phases . in phase
i , the frequency of type 1 was much higher than type 2 . in phase iib ,
type 2 was more frequent than type 1 , because the mid - portion of the tongue typically dipped instead of remaining in contact with the palate . in phase iii ,
all subjects displayed a continuous upward trace in m - mode images of phase iia during 3 saliva swallows .
for this reason , spatial and temporal measurements of phase iia were made from the m - mode images .
the swallow - related radial displacement of the mid - tongue surface during phase iia was measured , as well as the duration of tongue movement ( figure 7 ) .
type 1 . prior to swallow initiation , the tongue tip contacted the maxillary teeth or the incisive papilla , and the posterior portion of the tongue was raised cranially . during swallow initiation , the central part of the tongue moved with a caudal concavity that appeared as a downward slope in the m - mode tracing .
both the anterior and mid - portions of the tongue remained in contact with the hard palate .
the m - mode images demonstrated an easily identifiable hyperechoic horizontal line formed by the contraction of the tongue muscles ( figure 3 ) .
the mid - portion of the tongue moved upwards to contact the palate in this phase . an upward slope in m - mode traces
was found in every subject , and no variations were detected ( figure 4 ) .
the mid - portion of the tongue remained in contact with the palate , which was represented by a horizontal trace in m - mode images .
compressive peristaltic waves of the tongue surface producing an inverted  v  trace ( a downward slope followed by an upward slope ) in the m - mode images .
the mid - portion of the tongue moved downwards then upwards to return to the state of rest at the end of the oral swallowing process . in the m - mode images ,
a downward slope was recorded in phase iiia and was always followed by an upward trace in phase iiib , which appeared as a  u  or  v.  type 2 .
the mid - portion of the tongue returned to the rest state . in the m - mode images ,
phase iiia revealed a downward trace that was then followed by a horizontal line during phase iiib .
the tongue dorsum remained on the palate after swallowing . in the m - mode images , both phases iiia and iiib demonstrated a single horizontal trace ( figure 6 ) .
in phase i , the frequency of type 1 was much higher than type 2 . in phase iib ,
type 2 was more frequent than type 1 , because the mid - portion of the tongue typically dipped instead of remaining in contact with the palate . in phase iii ,
all subjects displayed a continuous upward trace in m - mode images of phase iia during 3 saliva swallows .
for this reason , spatial and temporal measurements of phase iia were made from the m - mode images .
the swallow - related radial displacement of the mid - tongue surface during phase iia was measured , as well as the duration of tongue movement ( figure 7 ) .
figure 8 shows the average swallow - related radial displacement of the mid - tongue surface during phase iia .
the average displacement gradually decreased with age in both females and males , but these trends did not reach statistical significance among the 3 age groups ( p=0.116 and p=0.726 , respectively ) .
however , males demonstrated a significantly greater degree of displacement than females across all age groups ( p=0.002 , p<0.001 , and p<0.001 , respectively ) .
the average duration during phase iia gradually increased with age in both females and males , although these trends did not reach statistical significance among the 3 age groups ( p=0.284 and p=0.237 , respectively ) .
however , males had a significantly longer swallowing duration than females across all age groups ( p<0.001 , p<0.001 , and p<0.001 , respectively ) .
the stages of swallowing are divided into oral , pharyngeal , and esophageal phases . because ultrasonography is not well suited to analyze the esophageal and pharyngeal phases , our study is limited to the oral phase only . because the floor of the mouth is an accessible and relatively small area ,
ultrasonography is able to provide valuable information about deglutitive tongue movements , and the b+m - mode imaging technique allows us to depict tongue muscle contractions and positional changes of the tongue surface as time - amplitude diagrams . in this study , the cushion scanning technique ( a latex bag filled with water placed under the chin )   was not used because this stabilizing design increases the distance between the transducer and the floor of mouth , and the dispersal of the ultrasound waves through the cushioning layer could decrease image resolution . instead
, our subjects were examined in the upright position with the head and transducer fixed by a special device , which ensured that the subject s head and transducer remained in a constant position .
furthermore , because the volume , taste [ 3436 ] , consistency , and position   of the bolus being swallowed affect tongue movements , the subjects were instructed to perform saliva swallows and drink 35 ml of water between the swallowing to create the most reproducible swallows . in the m - mode images , it is practically impossible to find 2 subjects with identical swallow - related traces , as there are variations in tongue innervation , size , and anatomy of the oral cavity .
the subjects in our study differed in both age and sex , and we observed both inter - individual and intra - individual differences during the 3 saliva swallows for each subject .
although characteristic variants were observed in most of the individual m - mode swallowing phases , phase iia was depicted as a steep upward trace in all subjects .
saliva in phase i , the tongue moves upward to contact the palate in phase iia .
since no variants were found in this phase , we considered spatial and temporal measurements of phase iia as the optimal common measurement reference .
most early studies have compared the parameters of the m - mode traces between normal subjects and patients with dysphagia .
catriona et al . found that tongue movements during swallowing have age - related changes . in our study , the swallow - related radial displacement and duration of phase iia in the m - mode images were measured and compared across the 3 age groups .
it was suggested that the amplitude of phase iia decreased gradually with age , while its duration increased gradually with age .
these trends were not statistically significant across age groups . because the effect of age on tongue movement is small , this method of assessing swallowing function
, statistically significant sex - related differences were observed in both the amplitude and duration of tongue movement during phase iia in all 3 age groups .
male subjects demonstrated longer tongue movement distance than females , which could potentially be due to overall larger tongue size and stronger muscular contractions .
males also showed a longer motion duration than females , which could be related to heightened sensitivity of the sensory receptors of the male respiratory tract .
deglutitive tongue movements are frequently examined using videofluoroscopy in ent and speech therapy . according to watkin
however , when deglutitive tongue movements were investigated by b+m - mode ultrasonography in the past , researchers encountered inherent ultrasonographic limitations , such as artifacts , noise , refractions , and extraneous reflections .
furthermore , as the m - mode traces themselves varied significantly , it has been difficult to determine common features or establish measurement references , which has hindered the application of b+m - mode ultrasonography .
our findings suggest that the spatial and temporal measurements of phase iia within the m - mode traces can be used as the common measurement reference .
this investigation is limited to swallowing in the oral phase , since b+m ultrasound is not particularly well suited to analyzing the pharyngeal and esophageal phase .
videofluoroscopy or cine - mri would be much more appropriate for such an analysis . despite its limitations ,
in the m - mode traces of tongue movement during swallowing , a linear upward slope was detected in phase iia , which could be readily quantitatively measured using real - time b+m - mode ultrasonography .
the swallow - related radial displacement of the tongue and the duration of phase iia can thus be used for comparison among various swallowing types and treatments to evaluate outcomes .
this method can serve as a practical , noninvasive tool for preliminary evaluation of tongue deglutitive movements .
 backgroundthe purpose of this study was to evaluate tongue movements during swallowing in healthy adults using the b+m - mode ultrasonography , and to determine a common feature in the m - mode traces for quantitative measurement and individual comparison of tongue movements.material/methodsninety healthy subjects were divided into 3 groups according to age ( 2039 , 4059 , and 6080 years ) . 
 the tongue movements during 3 saliva swallows were examined using real - time b+m - mode ultrasonography . 
 the m - mode traces of tongue movements were recorded and evaluated.resultsboth intra - individual and inter - individual differences were detected in the m - mode traces during the 3 saliva swallows . 
 characteristic types were seen during the individual swallowing phases of m - mode traces : 2 activity types in phase i , 2 types in phase iib , and 3 types in phase iii . 
 however , no variations were seen during phase iia , in which all subjects displayed a continuous upsloping trace . 
 the average range of swallow - related tongue radial displacement during phase iia decreased gradually with age , while the average duration of tongue movement during phase iia increased gradually with age . 
 these 2 trends were not statistically significant across age groups . 
 however , differences between sexes were found in both the range of tongue radial displacement and the duration of deglutitive lingual actions during phase iia in all 3 age groups ( p<0.05).conclusionsb+m - mode ultrasonography may offer a quick and safe alternative for the preliminary evaluation of deglutitive tongue movements . 
Background
Material and Methods
Patients
Ultrasonography procedure
Statistical analysis
Results
B+M-mode images of tongue movements
(1) Phase I
(2) Phase II a
(3) Phase II b
(4) Phase III
Range of tongue swallow-related radial displacement during phase IIa
Duration of tongue movement during phase IIa
Discussion
Conclusions