Experimental Assessment of the Gain Achieved by the Utilization of Time-of-Flight Information in a Positron Emission Tomograph (Super PETT I)

Abstract

The gain achieved in image quality by utilizing, in the image forming process, the time-of-flight information (TOF) of positron annihilation photons between their inception and detection was measured experimentally by means of a positron emission tomograph (PET)-Super PETT I. The measurements were carried out by imaging a 35 cm cylindrical uniform phantom containing different positron activity concentrations. The gain achieved through the incorporation of TOF information, defined as the ratio of variances in images reconstructed with and without TOF information, was found to be approximately 3 at the lowest activity concentration and 5-8 in the activity concentration range typically encountered in clinical studies especially in fast or dynamic studies. This increase in gain with activity was interpreted as resulting from the reduction of random coincidences when TOF information is used. Further image improvement is yielded by incorporating TOF information into the PET attenuation correction provided by the measurement of transmission of annihilation photons in the object imaged.

ASNC imaging guidelines/SNMMI procedure standard for positron emission tomography (PET) nuclear cardiology procedures

“…However, it has been shown that adding TOF capability can improve the statistical quality of the data (i.e., the noise). [12][13][14] For example, recent reports indicate that TOF imaging can improve noise and image quality in 13 N-ammonia perfusion imaging, 15 and therefore potentially improve image quality or even perhaps, in the future, reduce the dose needed to achieve a given image quality. In addition, as mentioned above, performing high-count rate cardiac studies with 3D scanners presents difficulties.…”

Instrumentation for Time-of-Flight Positron Emission Tomography

“…At that time, the three main groups involved in the development of ToF scanners were at CEA-LETI in France [26,27], University of Washington St. Louis in Missouri, USA [28,29], and the University of Texas, USA [30]. Other groups involved in ToF-PET research were the National Institute of Radiological Science in Chiba, Japan [31,32], and Washington University in Seattle, WA, USA [33].…”

Advantages of improved timing accuracy in PET cameras using LSO scintillator

“…However, the 1.1 cm axial extent of the phantom causes this measurement to significantly underestimate the contributions from random and scattered events that would be present in a whole-body FDG study. This paper also quotes data with activity concentrations of 0.7 µCi/cc, for which a variance reduction factor of 6.2 is measured [26]. This data better approximates a whole-body FDG study.…”

“…A number of the TOF PET cameras that were built in the 1980's measured the TOF variance reduction [22,[26][27][28]. Interpreting these data is difficult, as substantial noise reduction factors often come from three different places: 1) reduced random event rates because the hardware coincidence window is reduced, 2) reduced noise in the true events due to the TOF reconstruction algorithm, and 3) reduced noise in the random events due to the TOF reconstruction algorithm [22].…”

“…For the clinical PET imaging situations most common today, the measurements given in [26] best describe the expected TOF gains. That paper quotes, for a camera with 500 ps resolution, a factor of 3.4 variance reduction for a 35 cm diameter cylinder, 1.1 cm thick phantom with 0.12 µCi/cc activity concentration, which is extremely similar to the source diameter and activity density for a whole-body FDG oncology study (10 mCi evenly distributed in a 70 kg patient corresponds to 0.14 µCi/cc).…”