Evaluating doses of multi-slice CT in brain examinations using various methods

Figures & data

Figure 1. (a) CT of the Rando phantom in CT unit and details of TLD in (b) third section (c) seventh section and (d) the tenth section.

Figure 2. Scout view of two protocols obtained at Phillips Brillance 128-slice. (a) Axial scan: maxillae from external auditory meatus to parietal bone. (b) Helical scan: from mandible to parietal bone.

Table 1. Imaging parameters for two adopted protocols for brain CT routineexaminations.

Parameters	Axial scan	Helical scan
Potential (kV)	120	120
Tube current (mAs)	400	400
Rotation time (sec)	1.5	0.78
Collimation (mm)	10	40
Thickness (mm)	5	4.5
Detection configuration (mm)	16 × 0.625	16 × 0.625
Radiation angle	360	0
Scanned length (cm)	12.5	21.1
CTDIvol (mGy)	69.2	51.1
DLP (m Gy cm)	865	1078.2
Acquisition time (sec)	25.5	5.9

Table 2. Weighting factor (W_T) of organ or tissue recommended by ICRP 60 and 103 as well as number of TLD-100H imparted in Rando phantom.

Organ/Tissue	Measured Points	ICRP 60	WT	ICRP 103	WT	Number of TLD
Thyroid	Thyroid	0.05	0.05	0.04	0.04	6
Brain	Brain		0.007	0.01	0.01	39
Salivary	Salivary	0.007	0.007	0.01	0.01	9
Bone marrow		0.12		0.12
	C-spine		0.06		0.06	6
	Thighbone femur		0.06		0.06	3
Lung	Lung	0.12	0.12	0.12	0.12	3
Skin	Skin	0.01	0.01	0.01	0.01	15
Esophagus	Esophagus	0.05	0.05	0.04	0.04	3
Breast	Breast	0.05	0.05	0.12	0.12	0
Bone surface		0.01	0.01	0.01	0.01	3
Liver	Liver	0.05	0.05	0.04	0.04	3
Colon	Colon	0.12	0.12	0.12	0.12	3
Stomach	Stomach	0.12	0.12	0.12	0.12	3
Bladder	Bladder	0.05	0.05	0.04	0.04	3
Gonads	Gonads	0.20	0.20	0.08	0.08	3
Remainder		0.05		0.12
	Lens		0.007		0.024	6
	Heart		0.007		0.024	3
	Pancreas		0.007		0.024	3
	Kidney		0.007		0.024	3
	Small intestine		0.007		0.024	3
Total			1.000		1.000	120

Figure 3. Equivalent doses of organs or tissues (mSv) of the two protocols: The bar presents counting errors.

Table 3. listed organ or tissue doses (mSv) for 128-slice CT using axial and helical scan.

Organ/tissue	Axial scan	Helical scan
Brain	52.8 ± 6.3	28.5 ± 2.4
Lens	50.8 ± 7.1	30.8 ± 3.4
Nasal bone	39.8 ± 4.0	24.2 ± 4.6
Salivary gland	4.45 ± 0.97	45.6 ± 2.6
Bone marrow	5.90 ± 2.18	22.5 ± 1.80
Esophagus	0.47 ± 0.07	6.56 ± 1.67
Thyroid	0.64 ± 0.18	4.45 ± 0.58
Lung	0.09 ± 0.02	1.48 ± 0.31
Heart	0.03 ± 0.01	0.07 ± 0.02
Stomach	0.02 ± 0.01	0.02 ± 0.01
Pancreas	0.03 ± 0.01	0.04 ± 0.02
Liver	0.02 ± 0.01	0.03 ± 0.01
Colon	0.05 ± 0.03	0.04 ± 0.02
Kidney	0.03 ± 0.01	0.05 ± 0.03
Small intestine	0.02 ± 0.01	0.02 ± 0.01
Gonads	0.03 ± 0.02	0.03 ± 0.01

Figure 4. Calculation of E of the two protocols by different methods: TLD-100H approaches as recommend by ICRP 60 and 103;DLP method as recommend by AAPM 96. Error bar represented as counting errors.