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Stabilization of red blood cell aggregation evaluation using short-axis
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BRIEF NOTEJapanese Journal of Applied Physics 60, SDDE08 (2021)
https://doi.org/10.35848/1347-4065/abf3d5

Stabilization of red blood cell aggregation evaluation using short-axis view of veinof ultrasoundAkiyo Fukase1, Kyohei Higashiyama1, Shohei Mori2, Mototaka Arakawa1,2*, Satoshi Yashiro3, Yasushi Ishigaki3, andHiroshi Kanai1,2
1Graduate School of Biomedical Engineering, Tohoku University, Sendai, Miyagi 980‑8579, Japan
Graduate School of Engineering, Tohoku University, Sendai, Miyagi 980‑8579, Japan3
Department of Internal Medicine, Iwate Medical University, Shiwa, Iwate 028-3695, Japan2*

E-mail: arakawa@ecei.tohoku.ac.jp

Received December 2, 2020; revised February 16, 2021; accepted March 31, 2021; published online April 15, 2021
Red blood cell (RBC) aggregation is the reversible adhesion of RBCs among themselves. We previously reported a positive correlation between
blood glucose level and the degree of RBC aggregation (the brightness of the B-mode image). In the present study, we investigated thecontribution to the brightness according to the deviation from the central axis in measurements along with the long-axis view of the vein. The results
show that the brightness changed significantly for a slight change in the lateral position in the short-axis image. We found that the stability of themeasurements was not guaranteed in the long-axis view and estimated the correct analysis window range for the short-axis view.
© 2021 The Japan Society of Applied Physics

Red blood cells (RBCs) adhere reversibly to each other inblood vessels with a low shear rate or stasis. The phenomenon is called RBC aggregation, and its progression can be
conﬁrmed by an increase in the brightness of the B-mode
image,1) which is a warning for thrombus formation in theheart chambers.2–4) The degree of RBC aggregation depends
on various factors that determine blood properties, such as
blood viscosity and hematocrit.5–7) There are many studies
using techniques such as in vitro experimentation8–15) andnon-invasive methods for evaluating blood properties.16–22)
However, it is difﬁcult to quantify, and the blood components
have not been evaluated using ultrasound so far. The
realization of non-invasive and quantitative evaluation ofblood properties will be useful for monitoring blood properties in patients in cases where blood sampling is difﬁcult23)
and for checking blood glucose levels for daily treatment indiabetics.24,25) Our previous studies have shown a positive
correlation between the degree of RBC aggregation (thebrightness of the B-mode image) and the blood glucoselevel,26) but the precision of blood glucose level determination using ultrasound was low. One of the causes wasconsidered to be the lack of ability to ﬁx position in theelevation direction of the measurement target during thelong-axis measurement.
We performed measurements along with the short-axis view
instead of the long-axis view of the vein.27) The brightness
distribution in the lateral direction of the short-axis image andthe stability of the repeated measurements were evaluated. In
the present study, the brightness distribution in the beam
direction of the short-axis image of the vein was also evaluatedand an analysis method that can perform a stable evaluation of
the degree of RBC aggregation was established.
The brightness of the intravascular B-mode image wasused as a parameter for evaluating the degree of RBC
aggregation. Considering the large propagation attenuationof ultrasound in the living body and ease of avascularization,
the dorsal vein of a person’s hand was selected as themeasurement target. Measurements were performed under
the conditions of natural blood ﬂow and avascularization inwhich RBC aggregation was likely to occur. Under thenatural ﬂow condition, the natural state of blood can beobserved. However, the obtained values greatly ﬂuctuateeven with the data measured at 1 s intervals due to the bloodﬂow. On the other hand, under avascularization, it is possible
to measure the brightness value of the vessel lumen in a morestable state with no blood ﬂow (0 mm s−1) although it is notpossible to observe blood in its natural state.
An ultrasound diagnostic apparatus (UD-8000; TomeyCorp., Nagoya, Japan) was used with a mechanical linear
ultrasound probe (IP210; Tomey Corp., Nagoya, Japan)
operating at the center frequency of 40 MHz and having a
focal length of 9 mm.
To investigate the lateral brightness distribution in thevessel lumen at rest, data for one frame was acquired. To
investigate the brightness distribution in the direction of theultrasound beam, data were acquired by changing the focal
position of the probe from the near wall to the far wall of thevein at intervals of 0.1 mm. The brightness distributions in
the vein were investigated under the conditions of rest andavascularization. At rest, RF echoes were obtained with acuff wrapped around the forearm without tightening andapplying pressure (0 mmHg). After that, RF echoes wereobtained 50 s after the start of avascularization, with a cuff
pressure of 120 mmHg on the forearm, to obtain the data
during avascularization. The subject was relaxed and ﬁxed in
an untightened mold that ﬁtted the entire arm. The reproducibility of the data was also examined by taking measurements in the short-axis view using the following protocol.
Ultrasound data for a frame were acquired 11 times at 3 sintervals. For each frame, the acquired RF signals wereenveloped and averaged within the area near the center of thevessel.
Figure 1(A) shows the B-mode images of the dorsal vein,and Fig. 1(B) shows the average brightness along the depth
direction in the area indicated by the red and green frames inFig. 1(A). The brightness was 20 dB around the center in thearea indicated by the red frame and it became darker when
the brightness reduced to 8 dB near the vessel wall. The
intima-media complex (IMC) is visible only when theultrasound beam is incident normal to the vessel wall.
From the brightness distribution in the lateral position, it
can be seen that a brightness gradient exists even in the range
where the IMC can be identiﬁed (the region between the twoyellow lines).

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Jpn. J. Appl. Phys. 60, SDDE08 (2021)

A. Fukase et al.

(a)

(b)

Fig. 1. (Color online) Brightness distribution in the lateral position in the dorsal vein at rest. (A) B-mode image; (B) brightness values for the lateral position.

Figures 2(A) and 2(B) show the results at rest. Similarly,Figs. 2(C) and 2(D) show those during avascularization.
Figures 2(A) and 2(C) show the brightness distributions in
the direction of the beam in the vein and Figs. 2(B) and 2(D)show the B-mode images at the time of data acquisition foreach depth, and the red dashed line is the focal point and theyellow frame is the analysis window. The left sides ofFigs. 2(B) and 2(D) correspond to the upper side (probe side).
Figures 2(A) and 2(C) show the brightness values, averaged
in the analysis windows (0.8 mm × 0.06 mm) shown in
Figs. 2(B) and 2(D), respectively, for the data acquired ateach position from the near wall to the far wall. The variation

(a)

(c)

(b)

(d)

Fig. 2. (Color online) Brightness distribution in the direction of the beam in the vein. (A), (B) at rest. (C), (D) at avascularization; (In (B) and (D), red dashedline: focal points, yellow frame: analysis window).

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A. Fukase et al.

Fig. 3. (Color online) Average brightness value for each frame.

in the averaged brightness values in the vein (at a depth of0.1–1.9 mm) at rest was 3.2 dB, and that in the vein (at adepth of 0.1–2.5 mm) during avascularization was 5.3 dB.
There was no sudden brightness change due to the change in
depth in the vein, both at rest and during avascularization.
However, a slightly higher brightness was observed at a
depth of 0.7 mm than at other depths at rest.
Figure 3 shows the average brightness around the center ofthe blood vessel for each frame. For each of the threemeasurements, the variation was within 2 dB. Moreover,
for all the measurements, the variation was within 2.5 dB.
In our previous experiments,26) scattering signals weremeasured along with the long-axis view, and the data in theIMC visible range were used to evaluate the degree of RBC
aggregation. Figure 1(B) suggests that the result greatlychanges due to a slight change in the position of the veineven if the data from the IMC visible slice is acquired.
Therefore, there were large ﬂuctuations in the brightness
value measured in the long-axis view.
From the results of the brightness distribution in the beam
direction (Fig. 2), it can be observed that the brightness
decreased linearly with depth, and the change in brightness
increased during avascularization. This is because theattenuation of ultrasound increased as RBC aggregation wasenhanced.28)
Considering the shear rate (velocity gradient) distribution in
the radial direction of the blood vessel at rest, the brightness
distribution was expected to be higher in the center of thevessel and lower near the vessel wall in both the lateral andbeam directions,29,30) but such a result was not obtained in thebeam direction. It is considered that the brightness distribution
due to the shear rate gradient could not be detected as it was
smaller than the temporal brightness ﬂuctuation due to theblood ﬂow in the vein. Moreover, in the blood vessel andbelow the blood vessel, as shown in Fig. 1(A), both the sides
have lower brightness than that at the center. Therefore, thebrightness distribution would be affected by the shape of theblood vessel. The effects of refraction and interference, due tothe phase shift in the focused ultrasonic waves, caused bydifferent sound velocities of blood and tissues increased atboth ends of the blood vessel.
The brightness was higher at the depth of 0.7 mm(p = 0.03) at rest. This may be because the increased RBC
aggregation occurred due to: (1) stagnation of the blood ﬂow
due to some physiological causes, such as straining or
breathing, and (2) the passage of blood, including

accidentally increased RBC aggregation, due to changes inblood ﬂow accompanied by the opening and closing ofvenous valves.
The ﬂuctuation range of the brightness in the beam
direction was almost the same as that for repeated measurements at the same position except for the effect of theattenuation. Therefore, when the degree of RBC aggregation
is evaluated from the brightness, it is considered that there isno problem if the analysis window is set at the focal position,even if the center of the blood vessel deviates from the focal
point by approximately 0.2 mm.
The brightness distribution in the lateral direction was highnear the center of the blood vessel and the gradient was steep,
whereas, the gradient in the beam direction was gradual. It isnecessary to examine whether this is due to the inﬂuence ofthe shape of the blood vessels. Therefore, it is necessary tostrictly set the analysis window range in units of several
beams (with a beam interval of 0.08 mm) in the lateral
direction. As shown in Fig. 3, the data with small ﬂuctuations
were obtained from the temporal measurements in the shortaxis view. A slight variation in the blood ﬂow might be themain cause of these small ﬂuctuations. The permissible
ﬂuctuation range will be determined in subsequent work byconsidering the ﬂuctuation range of RBC aggregation due tothe changes in blood glucose level.
Acknowledgments
KAKENHI 19KK0100.

This work was partially supported by JSPS

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