A fundamental study for quantitative measurement of ultrasound contrast concentration by low mechanical index contrast ultrasonography.
OBJECTIVE
In high mechanical index (MI) contrast ultrasonography it has been shown that the power of contrast signal intensity (CI) has a strong linear correlation with the concentration of the ultrasound contrast agent under conditions of constant applied acoustic pressure. However, it is unclear whether the linearity is preserved in low-MI contrast ultrasonography. Thus, we investigated the relationship between ultrasound contrast concentration and CI in vitro.


METHODS
Solutions of the ultrasound contrast agents Definity and Imagent were prepared at concentrations of 0.5, 2, 8, 32, and 128 μl/l. Placing a jelly block between the transducer and the solution, the solutions were transmitted using pulse subtraction imaging with an MI of 0.05, 0.1, and 0.5. CI was measured in dB in a region of interest 3 mm in height placed just below the border between the jelly and the solution. Data were plotted using double logarithm scales, where the concentration was expressed in dB as 10 × log (concentration).


RESULTS
CI in dB had a strong linear correlation with concentration in dB for both agents with any MI. Best fitted slopes were close to 1, indicating that the power of CI is proportional to the concentration.


CONCLUSIONS
In low-MI contrast ultrasonography, the power of CI is proportional to contrast concentration, and CI in dB is logarithmic to the concentration. Thus, the microbubble concentration can be quantitatively measured even in low-MI contrast ultrasonography.
Department of Cardiovascular Medicine, Hokkaido University Graduate School of Medicine, Kita-15, Nishi-7, Kita, Sapporo, 060-8638, Japan. syamada@med.hokudai.ac.jp.
Satoshi
S
Yamada
Department of Clinical Research, Hakodate National Hospital, Hakodate, Japan.
Kaoru
K
Komuro
School of Allied Health Sciences, Osaka University Faculty of Medicine, Osaka, Japan.
Mariko
M
Taniguchi
School of Allied Health Sciences, Osaka University Faculty of Medicine, Osaka, Japan.
Ayumi
A
Uranishi
Department of Cardiovascular Medicine, Hokkaido University Graduate School of Medicine, Kita-15, Nishi-7, Kita, Sapporo, 060-8638, Japan.
Hiroshi
H
Komatsu
School of Allied Health Sciences, Osaka University Faculty of Medicine, Osaka, Japan.
Toshihiko
T
Asanuma
School of Allied Health Sciences, Osaka University Faculty of Medicine, Osaka, Japan.
Fuminobu
F
Ishikura
Department of Cardiovascular Medicine, Hokkaido University Graduate School of Medicine, Kita-15, Nishi-7, Kita, Sapporo, 060-8638, Japan.
Hisao
H
Onozuka
Department of Health Sciences, Hokkaido University School of Medicine, Sapporo, Japan.
Taisei
T
Mikami
Department of Cardiovascular Medicine, Hokkaido University Graduate School of Medicine, Kita-15, Nishi-7, Kita, Sapporo, 060-8638, Japan.
Hiroyuki
H
Tsutsui
School of Allied Health Sciences, Osaka University Faculty of Medicine, Osaka, Japan.
Shintaro
S
Beppu
contrast agent; contrast ultrasonography; mechanical index; pulse subtraction imaging