66

Japanese Journal of Comprehensive Rehabilitation Science (2017)

Brief Report

Scanning electron microscopy observations of rice cooked with nonionic water-soluble iodine for videofluoroscopic swallowing study
Masaru Konishi, DDS, PhD,1 Keiji Tanimoto, DDS, PhD2
Department of Oral and Maxillofacial Radiology, Hiroshima University Hospital, Hiroshima, Japan
Department of Oral and Maxillofacial Radiology, Graduate School of Biomedical and Health Sciences, Hiroshima
University, Hiroshima, Japan12

ABSTRACT
Konishi M, Tanimoto K. Scanning electron microscopy
observations of rice cooked with non-ionic watersoluble iodine for videofluoroscopic swallowing
study. Jpn J Compr Rehabil Sci 2017; 8: 66-70.
Objective: The aim of this study was to investigate thedistribution of contrast medium on and inside rice forvideofluoroscopic swallowing study (VFSS) as observedby scanning electron microscopy (SEM) and radiography.
We also examined the influence on texture of mixing thecontrast medium.
Methods: Cooked rice for VFSS was prepared using
non-ionic water-soluble iodine liquid (Visipaque® 270)and barium sulfate, and SEM and radiography wereperformed. Enhancement of the X-ray image wasevaluated using the gray-scale. The textures of hardness,adhesiveness, and cohesiveness were measured using atexture analyzer. The Kruskal-Wallis test and SteelDwass test were used to compare the measured values.
Results: On SEM, barium sulfate was only attached tothe surface of the rice but Visipaque® 270 was observed
inside the rice. The X-ray image of the rice cookedwith barium sulfate was mottled; however, Visipaque®
270 demonstrated uniform enhancement. The grayscale values of the X-ray images were statisticallydifferent (p < 0.001), whereas the textures showed nostatistical difference.
Conclusion: The rice cooked with Visipaque® 270
revealed good X-ray enhancement. This was because
the contrast medium was distributed not only on therice surface but also inside the rice.
Key words: videofluoroscopic swallowing study, cooked
Correspondence: Masaru Konishi, DDS, PhD
Department of Oral and Maxillofacial Radiology,
Hiroshima University Hospital, 1-2-3 Kasumi, Minami-ku,
Hiroshima 734-8553, Japan.
E-mail: mkonishi@hiroshima-u.ac.jp
Accepted March 23, 2017.
Conflicts of interest: The authors declare no conflict ofinterest associated with this manuscript.
©Kaifukuki Rehabilitation Ward Association 2017
doi.org/10.11336/jjcrs.8.66

rice, contrast medium
Introduction
For hospitalized patients with dysphagia, it is often
difficult to determine an appropriate dietary level, andthe food texture may not be suitable in terms of actual
swallowing function. Indeed, it is reported that 91% of
patients ingested a more restricted form of diet [1].
This may lead to a decrease in swallowing function
due to disuse atrophy of the swallowing organs.
Changing the form of food to an appropriate level is
one of the important factors for early discharge from
hospital and return to daily life. Cooked rice is a staple
food for Japanese people, and returning to meals
equivalent in texture to cooked rice is considered to be
an ideal goal for patients.
One of the causes of differences between swallowing
functions and appropriate food forms is that an
accurate evaluation of swallowing function is difficult.
Videofluoroscopic swallowing study (VFSS) isperformed as a guide when changing food forms.
Barium sulfate is the most commonly used contrast
medium for VFSS. When cooked rice is examined on
VFSS, the cooked rice is usually covered withpowdered or liquid barium sulfate. Because theappearance and texture of the rice are quite different
from those of the actual cooked rice, it is difficult toexamine the actual function of swallowing cookedrice.
The authors have been conducting research on
cooked rice with VFSS to examine a method of
accurately evaluating the swallowing of cooked rice.
We were able to prepare cooked rice suitable for VFSSin terms of appearance and texture by using a nonionic water-soluble iodine contrast medium [2, 3].
In the present study, we used scanning electron
microscopy (SEM) and radiography to investigate thedistribution of the contrast medium on and inside therice. We also examined the influence on texture ofmixing the contrast medium.

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Konishi M et al.: Rice cooked with non-ionic water-soluble iodine

Methods
1. Materials and sample preparation procedure
We used two kinds of contrast media, non-ionicwater-soluble iodine liquid (Visipaque® 270; DaiichiSankyo, Osaka, Japan) and barium sulfate (UmbraMD®; Fushimi, Kagawa, Japan). With reference to aprevious report [4], to make a small amount of cookedrice for one examination, we put the following amountsof materials in a small metal cup and cooked thesamples in a rice cooker (RC-10 LM®; Toshiba, Tokyo,Japan) [2].
Sample 1 was prepared as a control. The amounts ofSample 1 and Sample 3 were set in the same way as
the authors’ past report [2]. For Sample 2, bariumsulfate was set to the same amount as rice, and waterwas set to the same amount as Sample 1.
Sample 1: rice (10 g) + water (20 ml)
Sample 2: r ice (10 g) + barium sulfate (10 g) +water (20 ml)
Sample 3: r ice (10 g) + Visipaque 270® (10 ml) +water (10 ml)
2. Measurements
2.1 Observation with SEM
First, the surface of the raw rice before cooking wasobserved using SEM. Next, to investigate thedistribution of the contrast media, the surface and crosssection of rice immediately after cooking were observed
by SEM with reference to the method of Kobayashi etal. [5]. Furthermore, to investigate the shape and size ofthe particles of the contrast media, we observed Umbra
MD® and Visipaque® 270, respectively, using SEM. The
measurement conditions were set to an acceleration
voltage of 1.0 to 2.0 kV and a magnification of 30 to5,000 times.
2.2 Observation of all samples with dental X-raysystem
In order to assess the X-ray enhancement of cookedrice with contrast medium, radiographs (Xspot®; Asahi,Kyoto, Japan; YCR imaging plate®; Yoshida, Tokyo,Japan) of Samples 1, 2, and 3 were taken (Fig. 1). The
exposure conditions were set to a tube voltage of 60 kV,
a tube current of 20 mA, an irradiation time of 0.16 s,
and a focal distance of 20 cm. To evaluate the degreeof X-ray enhancement, the images were input to aFigure 1. X-ray radiography (a) and sample image (b).
(b) Upper, Sample 1; middle, Sample 2; lower, Sample 3.
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personal computer and the gray-scale values of 10
grains of rice were measured using Photoshop 7.0(Adobe Systems Inc., CA, USA). The average valuesand coefficients of variance (the standard deviation
divided by the average value) were compared between
samples.
2.3 Evaluation of textures of all samples
Textures of the samples were measured for hardness,adhesiveness, and cohesiveness using EZTest®
(Shimadzu, Kyoto, Japan). Each sample was placed ina cylindrical container with a diameter of 45 mm and aheight of 15 mm and compressed twice at a speed of
10 mm/s and a clearance of 5 mm using a plunger witha diameter of 20 mm and a height of 5 mm. Eachsample was left at room temperature for 30 minutes
after cooking and then measured. Measurements ofeach sample were performed five times and the averagevalues of five measurements were compared.
3. Data analysis
For the gray-scale value and its coefficient ofvariance of X-ray enhancement, the Kruskal-Wallis
test was used among samples and the Steel-Dwass
method was used for multiple comparisons. The
textures of hardness, adhesiveness, and cohesivenesswere examined using the Kruskal-Wallis test andSteel-Dwass method between the samples. A p-valueof <0.05 was considered statistically significant. For
all statistical analyses, JMP® 12 (SAS Institute Inc.,
Cary, NC, USA) was used.
Results
1. Observations with SEM
Many small foramina and fissures were observed on
the surface of the raw rice before cooking. The widthsof the fissures and foramina ranged from 1 to 10 μm(Fig. 2 a, b). Many small foramina were present on thesurface of Sample 1 after cooking (Fig. 2 c). In Sample
2, the barium sulfate was only on the surface of therice and was not observed inside the rice (Fig. 2 d, e).
In the cross-sectional image of Sample 3, the fissuresand a number of precipitates of iodixanol, which is acontrast component of Visipaque® 270, were observed(Fig. 2 f, g). SEM images of the contrast media particles
are shown in Fig. 3. The sizes of the barium sulfate
particles were approximately 20-260 μm in diameter(Fig. 3 a, b), and the particles of iodixanol wereapproximately 2 μm in diameter (Fig. 3 c, d).
2. Observations with X-ray images
Radiography confirmed that both Samples 2 and 3
showed contrast compared to Sample 1 without acontrast medium; however, Sample 2 was enhancedwith a mottled appearance compared to Sample 3 (Fig.
4). The measurement results of the gray-scale values
were 108.4 ± 10.0 for Sample 1, 215.0 ± 41.6 for
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Konishi M et al.: Rice cooked with non-ionic water-soluble iodine

Figure 2. SEM images of raw rice and all samples.
(a), (b) SEM surface images of raw rice, (a) ×30, (b) ×1,000. (c) SEM cross-sectional image ofSample 1, ×500. (d), (e) SEM cross-sectional images of Sample 2, (d) ×30, (e) ×500. (f), (g)SEM cross-sectional images of Sample 3, (f) ×30, (g) ×500.
(a) Many fissures on the rice surface (×30). (b) Width of fissure and foramen: 1-10 μm (arrow).
(c) Many small foramina on the rice surface (arrow). (e) Barium sulfate only attached to thesurface of the rice (arrow). (g) Grains of iodixanol (arrow).
Sample 2, and 238.1 ± 25.6 for Sample 3. All values
were expressed as mean ± standard deviation. A
statistically significant difference (p < 0.001) was
observed between all samples. The coefficient ofvariance was 9.2% in Sample 1, 19.3% in Sample 2,and 10.8% in Sample 3. Sample 2 containing barium
sulfate showed the largest variation in gray-scalevalue. There was no statistically significant differencein variability between Samples 1 and 3; however, there
were statistically significant differences between
Samples 1 and 2 and Samples 2 and 3 (p < 0.001).
3. Measurements of rice textures
The rice texture measurement results are shown inTable 1. The values of hardness, adhesiveness, andcohesiveness were not significantly different among
the three samples.

Discussion
SEM confirmed that iodixanol particles, which are
the imaging components of Visipaque® 270, weredistributed inside the cooked rice but barium sulfate
particles were only attached to the surface of thecooked rice. According to the report of Iida et al. [6],when observing cooked rice for VFSS with micro-CT,
the barium sulfate only adhered to the surface of therice. In Visipaque®, contrast media penetration into therice was not observed although the boundary between
the contrast medium and the rice was unclear,suggesting that the particles of barium sulfate andVisipaque® were too large to penetrate into the surfaceof the rice. According to our results, the sizes of thebarium sulfate particles were approximately 20 to 260
μm in diameter. This concurs with the idea that theparticles were large and could not penetrate into theJpn J Compr Rehabil Sci Vol 8, 2017

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Figure 3. SEM images of Umbra MD® (a, b) and Visipaque® 270 (c, d).
(a) Umbra MD®×50, (b) Umbra MD® ×300, (c) Visipaque® 270 ×1,000, (d) Visipaque®
270 ×5,000.
(a), (b) Various sizes of a barium grain. (d) Size of an iodixanol grain: 2 μm (arrow).

Figure 4. X-ray images of all samples.
Upper, Sample 1; middle, Sample 2; lower, Sample 3.
rice. On the other hand, the Visipaque® particles wereobserved inside the cooked rice. This was due todifferences in magnification and resolution between
micro-CT and SEM, i.e., the Visipaque® particle size
was too small to detect by micro-CT. Many cracks
have been reported to exist on the surface of rice
before cooking [5] and cracks with a width ofapproximately 1.0 to 10.0 μm were observed on SEM
in the present study. It was found that the particle size

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of iodixanol was approximately 2 μm in diameter andso it could be considered that it was able to penetrate
into the rice from the cracks. Furthermore, since
iodixanol is soluble in water [7], it is conceivable that
iodixanol dissolved in water is absorbed inside the rice
during the cooking process and then precipitatedinside the rice as particles after water evaporation. The
radiographic images of Sample 3 revealed uniform
enhancement and the coefficient of variance of thegray-scale value was low. This is considered to be a
uniform and highly contrasting value because particlesof iodixanol (C35H44I6N6O15, molecular weight
1,550.19 [7]) were also distributed inside the rice. On
the other hand, Sample 2 exhibited non-uniform
enhancement and the coefficient of variance of thegray-scale value was also significantly larger than thatof the other samples. A large variation in concentrationmeans that portions with a large difference in X-ray
absorption are adjacent to each other. As describedabove, in an area where a black portion with highradiolucency and a white portion with radiopacity arein contact, the white portion in contact with the black
portion appears whiter in color and the black portionin contact with the white portion appears blacker(Mach effect) [8]. That is, if the contrast density varies
as in Sample 2, the black part in which the contrast
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Table 1. Textures of samples.
Hardness (×104 N/m2)

Adhesiveness (×103 J/m3)

Cohesiveness4.22 ± 1.97
5.12 ± 1.80
3.67 ± 1.34

6.61 ± 3.76
4.26 ± 2.66
7.26 ± 1.99

0.11 ± 0.06
0.16 ± 0.11
0.20 ± 0.11

Sample 1
Sample 2 (Ba)Sample 3 (I)Data presented as mean ± standard deviation.
There were no significant differences (Kruskal-Wallis test; hardness, p = 0.417; adhesiveness,p = 0.229; cohesiveness, p = 0.491).
medium does not adhere may look darker. Because theimage of the rice may not be accurately viewed at thetime of swallowing on VFSS, aspiration could bemissed.
Regarding the textures of hardness, adhesiveness,and cohesiveness, no statistical differences were foundamong all samples. According to the reference valuesof hardness and adhesiveness for patients withswallowing difficulty given by the Japanese Ministryof Health, Labour, and Welfare [9], all samples in thepresent study can be judged as being at the level ofordinary food rather than food that is difficult toswallow. Although no differences were found withrespect to the textures of hardness, adhesiveness, andcohesiveness in the present study, the evaluation andimprovement of texture and taste as sensed by patientsremain future challenges.
Conclusions
In this study, SEM observation confirmed that thecontrast medium was distributed not only on thesurface of the rice but also inside the cooked rice for
VFSS using Visipaque® 270. Furthermore, the contrast
medium demonstrated good enhancement of X-ray
images. Regarding food textures, there were nodifferences between the rice cooked with Visipaque®
270 and normal rice. Therefore, we plan to perform
VFSS using rice with Visipaque® 270 for clinicalefficacy and safety.

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