Page 65 - ARNM-2-2

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

The purpose of our study was to evaluate the overall
effect of varying tube currents at constant tube voltage and
varying tube voltage at constant tube current on the amount
of noise produced in each protocol. We wanted to find
out whether it is possible to vary the tube voltage when
maintaining the same image quality without a substantial
change in noise level. 4

All noise measurements are presented in Table 1, the
pairing of 70 kV with 10 mAs as shown in part (A) shows
a noise level that is noticeably lower than the level resulted
by the pairing of 70 kV with 10 mAs as shown in part (B),
despite the equivalent radiation dose.
Figure 5. Noise measurements demonstrating an inverse relationship
between tube current (kV) and noise at a constant radiation dose The results of this present study are consistent with
previous studies that demonstrated that the use of high
kVp should be accompanied with low mAs values as the
level of noise is associated with higher tube voltage and
that the noise decreases with an increase in tube voltage at
constant mAs. 10,17,23,26,28 These findings are instrumental for
the optimization process.
Certain parts of the findings from this study are peculiar
to the Planmeca ProMax 3D Mid CBCT unit (Planmeca,
Helsinki, Finland); therefore, this subset of findings is not
generalizable to other CBCT systems. Thus, the optimized
tube voltage applied for each CBCT model is expected to
be unique, depending on factors such as total filtration
and other sources of noise other than scatter and quantum
noise.
Figure 6. Noise measurements demonstrating an inverse relationship
between tube voltage (kV) and noise according to a power function In general, research on existing CBCT devices is limited
by the available options of exposure parameters such as
(combinations of) exposure settings for this particular CBCT kVp, many of which have a fixed kVp and allow only a few
system (Planmeca ProMax 3D Mid CBCT unit, Planmeca, preset tube current options. Hence, applying varying tube
Helsinki, Finland), but the principle can be extended to any voltage under a fixed tube current is not feasible for such
However, the optimization method applied in
models.
15,29
CBCT device, ideally during commissioning study of the this study and the overall results are generally applicable.
device.
The results of computed tomography (CT) studies by Optimization for a particular CBCT scanner should
Akinlade et al., which showed that the highest selectable begin with identifying the optimal tube voltage value. The
tube current for a specific scanner is optimal in terms values correspond to the typical clinical tube potential
of balancing image quality, radiation dose, and hence settings at which the clearest and least noisy image is
30
the noise, were verified in the first part of this analysis. produced, subsequently a gradual increase in the mAs to a
26
However, in the second part of this study, we found that value that is minimally suitable for a given diagnostic task.
the noise had increased by 0.09% in comparison with However, we were able to show that higher tube voltage
the same standard exposure protocol used in the first settings (80, 75, and 70 kV) resulted in significantly lower
part. This performance level was found to be within the noise levels and ultimately led to a subjectively higher
30
acceptable limit of ≤ ±10%, as stated by the Malaysian image quality.
Ministry of Health. However, to our knowledge, there is The application of a combination of many energy-
27
no clear guideline on the percent difference between the dependent X-ray interactions has led to increasing nuances
first protocol (constant tube voltage with varying tube and complexity in noise production and hence image
current) and the second protocol (constant tube current quality as a result of the changes to tube voltage. A lower
and varying tube voltage). tube voltage value increases not only the noise level but

Volume 2 Issue 2 (2024) 5 doi: 10.36922/arnm.2972