The Design of Diagnostic Medical Facilities where ... - ResearchGate

R D(t)
= . t D(0) × t
Equation 5.8
T
= 1.443×
t
½
×
1−
exp
− 0.693t
T
½
where D(t) = Total dose (μSv) over a time t at 1 m from the patient
Ḋ(0) = Dose rate (μSv/h) at 1 m at the time of administration,
given by the product of the dose rate constant for the patient
(0.092 μSvm 2 /MBqh for 18 F) and the administered activity A 0
(MBq)
t = Time (min) of interest
T ½
= Half life (min) of the radionuclide
For 18 F, this corresponds to R t
factors of 0.91, 0.83, and 0.76 for t = 30, 60, and 90 min, respectively.
Decay before Imaging
Because of the decay since the administration of the radionuclide (uptake phase), the activity in the patient
at the commencement of imaging is decreased by
F = exp
u
-0.693t
T
½
u
Equation 5.9
where t u
is the uptake time (min) and T ½
is the half life (min)
Physiological decay
In most cases the patient will void prior to imaging, removing approximately 15% of the administered activity
and thereby decreasing the dose rate by 0.85.
Calculation of exposure at a boundary
Equation 5.7 may be used for the calculation of total exposure at a boundary, a distance d metres, from the
patient.
Uptake room
The total dose (μSv), at a distance d (m), from a patient during the uptake time, t u
(min), will be given by
R
D(t
u
) = D(0)
. × tu
×
d
tu
2
Equation 5.10
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The Design of Diagnostic Medical Facilities where Ionising Radiation is used