Method for improving clinical data quality in positron emission tomography
A method for improving clinical data quality in Positron Emission Tomography (PET). The method provides for the processing of PET data to accurately and efficiently determine a data single-to-noise ratio (SNR) corresponding to each individual clinical patient scan, as a function of a singles rate in a PET scanner. The method relates an injected dose to the singles rate to determine SNR(D inj ),and provides an accurate estimate of a quantity proportional to SNR, similar in function to the SNR(D inj ). Knowledge of SNR(D inj ) permits determination of peak SNR, optimal dose, SNR deficit, dose deficit, and differential dose benefit. The patient dose is fractionated, with a small calibration dose given initially. After a short uptake, the patient is pre-scanned to determine T, S, and R. An optimal does is then determined and the remainder injected.
1. A method for improving clinical data quality in Positron Emission Tomography (PET), said method comprising the steps of:
(a) injecting a patient with a calibration dose of a radiopharmaceutical, said calibration dose being a fractionated portion of a patient dose of the radiopharmaceutical;
(b) pre-scanning the patient;
(c) determining a trues rate (T pat );
(d) determining a scattered events rate (S pat );
(e) determining a randoms rate (R pat );
(f) determining a singles rate s pat meas ;
(g) determining an optimal dose of the radiopharmaceutical using T pat , S pat , R pat and s pat meas ;
(h) determining a remainder dose as a difference between said optimal dose and said calibration dose; and
(i) injecting said patient with said remainder dose.
2. The method of claim 1 wherein said step of determining a trues rate is performed by:
T
pat
(
s
)
=
T
pat
(
s
pat
meas
)
T
phant
(
s
pat
meas
)
T
phant
(
s
)
;
wherein said step of determining a randoms rate is performed by:
R
pat
(
s
)
=
R
pat
(
s
pat
meas
)
T
phant
(
s
pat
meas
)
T
phant
(
s
)
;
and
wherein said scattered events rate is included in determining said trues rate such that:
(
T
+
S
)
pat
(
s
)
=
(
T
+
S
)
pat
(
s
pat
meas
)
(
T
+
S
)
phant
(
s
pat
meas
)
(
T
+
S
)
phant
(
s
)
;
wherein s is a total measured singles rate.
3. The method of claim 2 wherein T(s) and R(s) are measured for a given scanner at at least one value of s using a phantom.
4. The method of claim 2 wherein T(s) closely approximates (T+S)(s) in shape and wherein (T+S) defines a net trues rate, wherein (T+S) is measured directly, and wherein said trues rate is estimated by subtracting an estimate of a mean scatter distribution.
5. The method of claim 2 wherein said randoms rate is estimated using one of a group of methods including at least estimating said randoms rate directly from a delayeds sonogram, estimating said randoms rate as a fraction of a total delayeds rate assuming a uniform distribution and using an attenuation mask, and estimating said randoms rate form a spatial distribution of said singles rates.
6. The method of claim 2 further including the step of estimating a single-to-noise ration (SNR) as a function of said singles rate.
7. The method of claim 6 further including the step of relating said calibration dose to said singles rate by calibrating a phantom measurement of activity compared to said singles rate for a single patient acquisition to determine a dose response curve as:
A
pat
(
s
)
=
A
pat
(
s
pat
means
)
A
phant
(
s
pat
Meas
)
A
phant
(
s
)
,
where A represents one of a total activity and a mean activity concentration per mass or volume.
8. The method of claim 7 wherein A is a monotonic function of s, wherein said calibration dose is related to A by a decay factor and excretion fraction, said method further comprising the step of substituting said calibration does for A.
9. The method of claim 1 further comprising the step of developing a database relating patient characteristics including at least weight, body mass index, sex, disease, diabetes state, and anatomical position to optimal dose and peak SNR.
10. The method of claim 9 further including the step of statistically correlating said optimal dose for each scan completed into said database.
11. The method of claim 9 further including the steps of:
(a) comparing said patient characteristics for a new patient with said database; and
(b) estimating said optimal dose for said new patient.