We have developed a penile nonimaging scintillation (PNIS) probe consi
sting of a plastic well-type scintillation crystal interfaced to a por
table computer and acquisition board. This report describes the design
of the PNIS probe, performance characteristics, mode of usage and ill
ustrative results which demonstrate its capabilities. Methods: With th
e PNIS probe, penile blood-pool studies were performed in nine patient
s utilizing 3.7 MBq (100 mu Ci) autologous Tc-99m-labeled red blood ce
lls (RBCs). Venous blood standards were assayed to enable conversion o
f the count rate to volummetric measurements. Washin of peripherally a
dministered Tc-99m-RBCs was mathematically analyzed to estimate penile
blood volume and cavernosal flow rate in the flaccid state. The rate
of change of penile blood volume after intracavernosal vasodilators wa
s used to generate measures of stimulated flow. Results: A major advan
tage of this device over the gamma-camera is a 3300-fold increase in c
ount rate sensitivity, which allows for markedly improved temporal res
olution while significantly reducing the radiopharmaceutical dosage. A
dditionally, the PNIS probe is portable, economical and is not depende
nt on operator-defined regions of interest. Count rate sensitivity is
relatively constant within the bore, with the exception of the proxima
l region adjacent to the opening, where geometric efficiency is reduce
d. Conclusion: The PNIS probe is an effective device for measuring pen
ile activity in radionuclide studies, allowing for acquisition of time
-activity curves of the penis during flaccid washin of peripherally la
beled red blood cells and after pharmacologic stimulation to induce er
ection.