ReviewQuantitative Brain PET: Comparison of 2D and 3D Acquisitions on the GE Advance Scanner
Introduction
Dramatic increases in the sensitivity of positron emission tomography (PET) scanners have been achieved by the implementation of 3D data acquisition. On the hardware side, most new PET scanners now have a retractable lead/tungsten septa that can be moved in or out of the field-of-view (FOV).1, 2, 3, 4 On the software side, improved scatter corrections schemes like the dual energy window and model-based techniques have been introduced to reduce the increased scatter component in the 3D PET signal.5, 6, 7, 8
Our objective was to evaluate the quantitative recovery of clinical parameters of interest using the 3D capability of the GE Advance PET scanner to perform the following radiotracer studies in patients: (1) [18F]fluorodeoxyglucose (FDG) studies to estimate regional glucose metabolic rate (rCMRGlc) in normal subjects and patients with neurological disease; and (2) [18F]fluorodopa (FDOPA) studies to asses the integrity of the presynaptic dopaminergic system by estimating striatal radiotracer uptake in parkinsonism and related conditions. The 2D and 3D performance characteristics of the GE Advance scanner have been previously published.9, 10 Using the CTI/Siemens (Knoxville, TN) ECAT-831 Neuro PET scanner in 3D mode, Cherry et al. have demonstrated the improved detection of cerebral blood flow changes.3 Rakshi et al. have published the improvements afforded by 3D implementation for [18F]fluorodopa studies using the ECAT 953B (CTI/Siemens) scanner.11 Quantitative as well as qualitative evaluation of the GE Advance scanner in 3D mode for FDG studies have been recently presented in brief forms.12, 13, 14 We now present the comparative results of 2D and 3D data acquisition modes for our [18F]FDG and [18F]FDOPA studies performed on the GE Advance scanner using the commercially supplied scatter correction.5 Scatter correction in 3D is a very active area of research and new algorithms are being developed and refined. Besides scatter effects, differences arise in 3D and 2D modes due to axial slice width, randoms, dead time, and out-of-field activity. The focus of this paper is to evaluate whether an overall quantitative improvement in brain PET images can be obtained in 3D mode on the GE Advance PET scanner.
Section snippets
Scanner Performance
GE Advance scanner was used for these studies (General Electric, Milwaukee, WI). The characteristics of this tomograph relevant to 2D and 3D are presented in Table 1. Axial field-of-view (FOV): 15.2 cm; Number of detector (bismuth germanate, BGO) rings: 18; Coincidence window width: 12.5 nsec. The scanner includes shielding (32-mm lead) on both front and back of the detector units to prevent detection of events from outside the scan planes. Slice thickness = 4.2 mm; pixel size = 2.3 mm; a 6 mm
Results
3D and 2D images for FDOPA are illustrated in Figure 1. A significant improvement in image quality for the 3D acquisition is evident (3D and 2D data were acquired for equal scan duration).
Fdg
We could not discern any spatial dependency in the rCMRGlc errors. However, the maximum errors were associated with ROIs having the smallest areas like pons and caudate nuclei. These larger errors could arise from the difference in 2D and 3D axial resolution and partial volume effects on small structures (<4 cm3). For most of the gray matter regions, the difference between 2D and 3D rCMRGlc ranged between −5 to +5%. The excellent correlation between 2D and 3D data sets suggests that for FDG/PET
Conclusions
The advantage of 3D PET scanning is governed by the type of study and the clinical or research question that is being posed. For neurotransmitter studies like FDOPA where the injected activity is small and constrained by the radiation dosimetry, 3D can substantially improve the scan data. In case of autoradiographic FDG studies, the injected dose is usually not a limiting criterion except if multiple studies on the same subject are planned. Nonetheless, the total study duration can be shortened
Acknowledgements
Dr. Ken Kazumata is the recipient of Veola S. Kerr Fellowship from the Parkinson’s Disease Foundation.
Dr. David Eidelberg is a Cotzias Fellow of the American Parkinson’s Disease Association.
This work was supported by NIH R01-01001 and by the National Parkinson Foundation.
References (28)
- et al.
The ECAT EXACT HRperformance of a new high resolution positron scanner
J. Comput. Assist. Tomogr.
(1994) - et al.
Physical performance of a positron tomograph for brain imaging with retractable septa
Phys. Med. Biol.
(1992) - et al.
Improved detection of focal cerebral blood flow changes using three-dimensional positron emission tomography
J. Cereb. Blood Flow Metabol.
(1993) - et al.
Optimization of PET instrumentation for brain activation studies
I.E.E.E. Trans. Nucl. Sci.
(1993) Scatter correction method for 3D PET using 2D fitted gaussian functions
J. Nucl. Med.
(1995)- et al.
A convolution-subtraction scatter correction method for 3D PET
Phys. Med. Biol.
(1994) - et al.
Correction for scatter using a dual energy window technique with a tomograph operating without septa
I.E.E.E. Med. Imag. Conf. Rec.
(1991) - et al.
Model-based scatter correction for fully 3D PET
Phys. Med. Biol.
(1996) - et al.
Performance characteristics of a whole-body PET scanner
J. Nucl. Med.
(1994) - et al.
Investigation of the performance of the General Electric Advance positron emission tomograph in 3D mode
I.E.E.E. Trans. Nucl. Sci.
(1996)