Page 64 - ARNM-2-2

Advances in Radiotherapy
& Nuclear Medicine Optimal tube voltage for dental CBCT

varying tube voltage ranging from 60 kV to 80 kV at an tube voltage (P = 0.7509). All noise measurements are
interval of 5 kV. For each scanning protocol, the noise presented in Figures 3-6.
produced from each CBCT scan was used to determine Considering the fact that the combination of constant
the technical image quality that the machine would tube voltage and varying tube current led to some levels of
generate during operation. For each mAs setting, the noise, which were lower compared with the combination
noise was determined and the relationship between mAs
and noise generated was obtained using a power function of constant tube current and varying tube voltage, the
(Equation I) for a constant tube voltage and a varying mAs, following protocols have been proposed as optimized:
while Equation II was applied for a constant mAs and a (1) to achieve lower noise with higher dose, apply these
varying tube voltage. These equations were derived from parameters 70 kV, 16 mA, and 10.51 s (168.16 mAs);
established experimental data using dental CBCT. 4,6,23-25 (2) to achieve higher noise with lower dose, apply these
parameters: 70 kV, 5 mA, and 10.51 s (52.55 mAs).
Noise = 808 × mAs −0.577 (I)
Optimizing the exposure parameters for CBCT
Noise = 808 × kV −0.632 (II) scanning of cephalometry was the aim of this study using
3. Results and discussion the level of noise generated. Two scanning protocols were
applied corresponding with two different levels of noise,
Table 1 shows the values of the set tube voltage and tube as determined through Equations I and II. The scanning
current, the mAs values measured by the electrometer, and method applied in the present study utilized the available
the noise calculated based on Equations I and II.

For the first scanning protocol, the constant 70 kV
protocol with varying tube current showed a significantly
lower noise level ranging from 41.99 to 82.16, compared
with the constant mAs and varying tube voltage with
the noise level ranging from 50.66 – 60.76, despite the
equivalent exposure time.
After assessment of noise using different tube current
settings, a tube current of 16 mA was found to be the
best value for this particular CBCT system. P < 0.05 was
considered statistically significant. Pairwise comparisons
revealed statistically significant differences between varied
tube voltages at constant mAs and varied mAs at constant

Table 1. Dosimetric parameters for the CBCT operator Figure 3. Noise measurements demonstrating an inverse relationship
settings, under a fixed source-to-detector distance of 120 cm between tube current-exposure time product (mAs) and noise at a
constant tube voltage (kV)
No. Set tube voltage Set tube current mAs Noise
(A) Fixed tube voltage and varying tube current
1 70 5 52.55 82.16
2 8 84.08 62.64
3 10 105.1 55.07
4 14 147.14 45.36
5 16 168.16 41.99
(B) Fixed tube current and varying tube voltage
6 60 10 105.1 60.76
7 65 57.76
8 70 55.12
9 75 52.77
10 80 50.66
Figure 4. Noise measurements demonstrating an inverse relationship
Abbreviations: mAs: tube current-exposure time product; between tube current-exposure time product (mAs) and noise according
CBCT: Cone-beam computed tomography. to a power function

Volume 2 Issue 2 (2024) 4 doi: 10.36922/arnm.2972