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PET

Introduction

PET-scanners have many variations in design and performance in comparison to gamma cameras. The systems range from a variety of detectors and  scanner configurations. For this reason, performance measurements and comparisons of different instruments is quite difficult. NEMA and IEC are continuously devising and updating standard tests for PET performance.  Basically these tests should be used by the manufacturers in their specifications of the instruments and also in the acceptance tests for a new scanner. The large variety of scanners will influence the content of a regular quality control programme which has to be designed for each single PET scanner  the department.  Usually the manufacturer will provide instructions on what tests to perform and will separate different aspects of a quality control programme into daily, weekly, and quarterly procedures. Daily tests monitor image quality for changes over time, weekly tests are more involved with detector outputs being corrected for, and quarterly calibrations are used to optimize system performance. Routine QC should track system stability and be able to detect changes in the scanners performance.

Important principles

A quality control programme for new equipment should start with an acceptance test to verify the specifications given by the vendor. The acceptance test should be performed according to accepted international standards and may require instruments and phantoms not available in the department. Because of the advanced nature of the PET-scanner, any of the acceptance test and regular checks should be performed by a specially trained medical physicist or by the manufacturer as part of a regular maintenance programme. Certain parameters should be tested daily, others on weekly, monthly and yearly basis. Recommendations given by international, national and professional organizations should be followed. Reference testing is particularly important in order to detect and correct long-term slow deterioration in quality.  Furthermore the complexity of the equipment and the nature of the routine clinical investigations demand frequent control to ensure the validity of results. For a PET-scanner this includes some operational checks, such as blank scan, normalization and calibration. Quality control of hybrid scanners (PET/CT) should also include a QC-programme for the CT. In addition, it is important to verify the accuracy of the registration techniques used by the hybrid PET/CT scanner.

Introduction to references

The IAEA has published a technical reference book that provides guidance about the specifications and prerequisites required for acceptance testing of PET and PET/CT scanners, including guidelines for routine quality control of the equipment. Following these guidelines would ensure operation of a scanner under optimal conditions. Other publications from IAEA (Safety Report Series No 58) discusses radiation protection matters related to PET/CT. International standards have been published by NEMA and IEC. Some information on QC of PET scanners can also be found on the IAEA Radiation Protection of the Patient web-site as well as in the presentations by Zanzonico.and O’Brien-Penney.