Measured Head CT/CTA Skin Dose and Intensive Care Unit Patient Cumulative Exposure

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Fig 1.
A, Acrylic skull phantom with nanoDots at forehead and lateral locations. B, Patient CT image with nanoDot on forehead.
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Fig 2.
PSD distribution for all 52 patient examinations on both scanners. PSD was very comparable between scanners for the same patient examination. On average, the PSD for CTA examinations was more than twice that of routine head CT examinations. Note that 2 data points coincide for examination 7 (head CT) and examination 12 (head CTA).
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Fig 3.
A, PSD and CTDI_vol for all patients examined on scanner 1. B, PSD and CTDI_vol for all patients examined on scanner 2. CTDI_vol overestimated PSD for all patient examinations on each scanner for both CTA examinations and routine head CT examinations.
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Fig 4.
PSD versus patient size for all patient examinations on both scanners. Patient size is specified as the effective diameter, calculated from anteroposterior and lateral thickness measurements of patient's head. There was no significant correlation between PSD and patient head size for corresponding patient examinations on each scanner.

Table 1:

Patient demographics by scanner

Table 2:

CT/CTA technique

Scan/Phase	Tube Potential (kVp)	Tube Current (mA)^{^a}	mAs_eff^{^a}	Rot. Time (sec)	Beam Width (mm)	Pitch	Scan Length (mm)
Scanner 1
Head CT
Head	120	450	450	1	16 × 1.2		195
Head CTA
Head	120	450	450	1	16 × 1.2		156
Premonitoring^{^b}	120	182	60	0.33	1 × 10		10
Monitoring^{^b}	120	182	60	0.33	1 × 10		10
CTA head	120	342	174	0.33	20 × 0.6	0.65	180
Delayed head	120	585	450	0.5	20 × 0.6	0.65	171
Scanner 2
Head CT
Head	120	250	286	0.75	32 × 0.5	0.65	160
Helical	120	250	286	0.75	32 × 0.5	0.65	160
Head CTA
Helical	120	250	286	0.75	32 × 0.5	0.65	160
Premonitoring^{^b}	120	50	25	0.5	4 × 0.5		2
Monitoring^{^b}	120	50	25	0.5	4 × 0.5		0
Helical	120	250	196	0.5	64 × 0.5	0.64	160
Helical	120	250	196	0.5	64 × 0.5	0.64	160

Table 3:

PSD and CTDI_vol from head CT/CTA by scanner (mGy)

Table 5:

Illustrative ICU patient CT/CTA and cerebral angiography exposures^{^a}

	Patient 1	Patient 2	Patient 3	Patient 4
No. of CTA	12	8	8	8
PSD (mGy)	1187	791	791	791
No. of head CT	2	7	4	18
PSD (mGy)	78	274	157	706
No. of cerebral angiograms	11	9	2	14
Cumulative skin dose (mGy)^{^b}	2667	1574	908	3261
Total skin dose, all exams (mGy)	3932	2639	1856	4758
Time interval for all exams (days)	30	18	16	31