Extraction and characterization of routine PET count rates

Single-count rates, which are given at each 500 ms interval in the list-mode of both cameras, were extracted from (i) routine PET exams previously recorded on the Vereos or Ingenuity camera after the injection of 3 MBq.kg^-1 of a ¹⁸F-labeled tracer (¹⁸F-FDG, ¹⁸F-Choline, or ¹⁸F-DOPA) and (ii) a cardiac exam recorded with a Vereos camera after the injection of 7 MBq.kg^-1 of Rubidum-82 at stress. The number of selected patients as well as the number of collected samples of single rates are reported in Table ​Table22 and this, for each tracer type and for each camera. As seen in Table ​Table2,2, the main patient characteristics were comparable between patients imaged with the Vereos and those imaged with the Ingenuity camera.

General patient characteristics and main PET parameters recorded or computed in the different groups imaged in clinical routine with the Vereos (digital-PET) or Ingenuity (analog-PET) camera and after the injection of 3 MBq.kg^-1 of current ¹⁸F-labeled tracers, with an additional patient imaged after the injection of 7 MBq.kg^-1 of ⁸²Rb on the Vereos camera. Continuous variables are presented with median values [minimum – maximum values after exclusion of outliers]

76

[67-82]

70

[67-75]

71

[71-77]

72

[70-76]

68

[65-69]

78

[74-84]

63

[59-69]

80

[77-81]

69

[65-72]

14

[12-17]

67

[65-74]

24

[17-25]

Whole

body

Whole

body

Single count rate

(Mcps)

8.1

[5.8-10]

14.2

[7.4-21.7]

19.2

[17.7-20.1]

4.6

[2.3-6.0]

7.6

[3.7-12.6]

10.5

[7.9-13.3]

4.6

[0.5 29.5]

2.9

[1.7-3.9]

6.2

[2.5-10.4]

9.0

[8.1-9.5]

2.9

[1.3-3.9]

5.1

[2.3-8.7]

7.2

[5.3-9.2]

3.0

[0.3-20.8]

631

[621-643]

677

[628-732]

713

[702-719]

328

[325-332]

11.36

[11.28-11.43]

11.6

[11.34-11.82]

11.7

[11.68-11.77]

11.01

[10.98-11.05]

A corresponding activity concentration of the NEMA phantom was computed for these single-count rates collected in patients by using the aforementioned function f_S → A described above. The distributions of these count rates and of corresponding activity concentrations were analyzed according to tracer type and camera type and while considering all samples of 500 ms interval recorded in all bed positions and in all patients. As depicted in Fig. ​Fig.3a,3a, b, this distribution is represented through box plots along with the display of median values and interquartile ranges, as well as with the maximal and minimal values after excluding the outliers (i.e., values higher than 1.5-fold the upper limit of the 3rd quartile or lower than 1.5-fold the lower limit of the 1st quartile). These maximal and minimal values of the box plots were deemed to reflect the upper and lower limits for count rate, as well as for activity concentrations.

Box-plot representation of a distributions of single-count rates collected during routine PET exams as a function of tracer type (¹⁸F-FDG, ¹⁸F-Choline, ¹⁸F-Dopa, Rubidium-82) and camera type (blue for Vereos and red for Ingenuity), b corresponding activity concentrations from the NEMA scatter phantom (i.e., obtained through the relationship displayed in Fig. ​Fig.2a),2a), with c examples of time-evolutions of the count rates recorded during whole-body PET exams with ¹⁸F-FDG and with ¹⁸F-Choline, and during dynamic exams focused on the pelvis region for ¹⁸F-DOPA and on the cardiac region for Rubidium-82