Now, advancement in MSCT technique permits CT examinations to be fast and easily implementation, and this leads to a potential increasing of radiation dose for patients. particularly, risk of cancer death and the radiation exposure from hepatic CT examinations have increased significantly due to dynamic-enhanced of multiple-phase computed tomography examination was performed constantly. Management patient dose is subsequently a main interest in MSCT abdominal examinations.
We find in this study that, the relation between CNR and CT dose index volume (CTDIvol) was a directly relation, which was compatible with Waaijer et al. [21, 22], they found that SNR2 was proportional to effective tube current and CT dose index volume. Though the average CNR was reduced whenever CT examination was executed at 80 KVP tube voltages with the same tube current adjusting, CNR ameliorated basically when selfsame CTDIvol was utilized.
Also we find in this study that CNR range was from 0.02 to 0.63 when used 80 KVP. Furthermore, the relative radiation dose obtained at 80 KVP and 380mAs was 37% of the relative radiation dose obtained at 120 KVP and 300 mAs. Thus, we assume that low KVP scanning as low as 80 KVP is available for a pediatric Abdominal computed tomography scanning without diagnostic accuracy loss when mAs is maximum than 300 mAs allowing radiation dose reduction by 29% to 37%. This results have agreement with American ACR abdominal CT (CNR for a pediatric was more than 0.5) [16].
One of the greatest substantial factors for abdominal computed tomography is LCD, specially when we are searching for little lesions of organs of Abdomen like, pancreas, liver, kidneys or spleen.
LCD also is related for contrast improved series, not only related for not improved series, because contrast between abnormal and normal tissue could only increasing lightly by the iodine [23].
The low contrast detectability subjective scores obtained with 80 KVP and 150, 200, 250, 300 and 380 mAs were not varying significantly from scores obtained with 120 KVP. Moreover, the low contrast detectability average score obtained with 80 KVP and 380 mAs was similar to the low contrast detectability average score obtained with 120 KVP and 300 mAs. From our results, reducing KVP from 120 to 80 KVP also may result in up to 37% dose reduction without degeneration low contrast resolution. Funama et al. [21] reported that a 35% reducing of radiation dose might be obtained with examination was assessed at 90 KVP instead of at 120 KVP without degeneration of low contrast detectability. Our results have agreement with Funama also suppose that the capability of using lower tube voltage in abdominal computed tomography thereby achieving decreasing of radiation dose while image quality is maintaining acceptable.
Verdun et al. [24] shown that there is a strong correlation significantly between the average measurements of CNR and the low contrast detectability subjective scores (r = 0.95, p < 0.05).
Increasing in image noise and decreasing in SNR which resulted from the decreasing of photon flux were considered the basic obstacle of low tube voltage technology.
In our study, we found that there is significant difference between 120 and 80 KVP regarding image noise (SD). Also, there is positive significant correlation between (1/noise) and mAs at 120 KVP (r = 0.967, p = < 0.001) and at 80 KVP (r = 0.927, p = 0.003), such as Waaijer et al. [13, 22] we showed that the tube current has correlative relationship inversely with image noise. In other expression, when the lower tube voltage strategy or lower tube current is performed, the increased noise will be obtained.
However, image noise, has a good effect on abdominal images quality as the region of abdomen is lower contrast inherently.
So, low tube voltage computed tomography scanning required settings of higher tube current to recompense for the photon slower number.
As well, new technologies must be evolved to obtained image noise reduction. Over last years, Sundry articles showed that filter back projection (noise decreasing filters) (FBP) [25,26,27,28], also reconstruction methods, like adaptation statistical iterative reconstruction technique (ASIRT) [29,30,31] can virtually help to decrease the Computed Tomography images noise with reducing radiation dose without degradation of image quality.
Study limitations
First, this results must be further confirmed for clinical using as that CT examination at low KVP (80 KVP) was only implemented in ACR phantom, but this solid phantom was not consider body composition variability, nevertheless, Marin et al. [32] reported that a technology of low tube voltage with 80 KVP might be performed to ameliorate the conspicuity of liver tumors of malignant hyper vascular while significantly reduction of radiation dose of patient.
Second, the incident X-ray beam attenuation in computed tomography depends on the body portion size that wants to be evaluated but our studies do not take into consideration body sizes differences; that is, most great exposure is wanted for fat patients to achieve the same image quality to that for thinner humans [33]. However, preceding studies with a phantom propose that the technique of low KVP is efficient for dose reducing of abdominal computed tomography for comparatively patients having body weight below 80 kg (light weight patient) [34].
Another part is that more humans existing with implants of high-attenuation, that can significantly reduce image quality by applying low KVP protocols continuously.
Third, the contentious usage of maximum high tube current shortens the life of the tube so it has a bad effect on the machine. In our present work we use high mAs until 380 mAs but we did not get to the maximum tube current.
Lastly, we only utilize the computed tomography dose index volume (CTDIvol) acquired from the picture archiving and communication system (PACS) via manufacturer to assess the radiation dose.
As a final of limitations we recommended to do this study with a protocol 80 KVP on patient for more assessment.