Generation of realistic HMPAO SPECT images using a subresolution sandwich phantom
Introduction
Historically, most rCBF SPECT images have been assessed by visual interpretation of 2D images through the brain. Such interpretation is subjective and dependent on the operator's understanding of normality. Consequently the technique of anatomic standardisation and comparison of patients with controls and/or other patient groups is increasingly used in clinical practice and research (Huang et al., 2003, Imabayashi et al., 2004, Matsuda et al., 2007, Van Laere et al., 2002b).
Several software packages are available that allow automated whole-brain analysis of brain SPECT studies based on anatomic standardisation. The Statistical Parametric Mapping (SPM) software package (Frith et al., 1997) is well-known, freely available and strongly supported by many brain imaging researchers (Stamatakis et al., 2002, Van Laere et al., 2002b). Much of the work in this study used SPM5. The application of other voxel- and VOI/ROI-based analysis techniques to rCBF SPECT is also popular (Huang et al., 2002, Imabayashi et al., 2004, Volkow et al., 2002).
Only a few studies have been carried out on several topics of interest related to the use of normal database comparisons. Topics of interest include the optimisation of various processing steps (e.g. reconstruction, anatomic standardisation, normalisation and comparison) and the portability of normal databases between gamma camera systems (Barnden et al., 2004, Matsuda et al., 2004, Van Laere et al., 2001). The conventional method of addressing these issues is to create what Van Laere et al. (2002a) refers to as ‘signal known exactly (SKE) conditions’ i.e. where the cerebral activity distribution is known. As it is the comparison and portability of normal brain images under study, an ideal hardware phantom should, when scanned, produce as close to a normal distribution as possible.
Existing commercially-produced hardware phantoms for radionuclide brain studies, notably the Hoffman phantom (Hoffman et al., 1990), are difficult to accurately and reproducibly adapt for lesion and activation studies. More importantly, the 4:1 ratio between the grey and the white matter volumes in the Hoffman phantom are inappropriate for HMPAO SPECT studies of normal function, where the ratio is approximately 2:1 (Wirestam et al., 2000). The cerebellum is a popular area for count normalisation; the phantom only includes the top part of the cerebellum which means scaling to peak or average cerebellar uptake is not possible.
In this study we have constructed a hardware phantom based on a stacked ‘sandwich’ design, modified slightly from the phantom used by Van Laere et al. (2002a), which was in turn based on a design by Larsson et al. (2000). The principle is based on discrete sampling of radioactivity in 3D objects by means of subresolution-spaced equidistant 2D planes, on which a priori-defined radioactive distributions are printed using radioactive dye. Previous studies using this type of phantom have concentrated on validation of scatter and attenuation correction techniques (Larsson et al., 2000) and performance assessment of neuroactivation studies (Van Laere et al., 2002a). Both used sections of the digitised mathematical Hoffman phantom as a cerebral template and neither study simulated the skull.
The aim of this study was to use a realistic cerebral template with a simulated skull to generate realistic HMPAO SPECT images. Ideally, the phantom projection data should be processed in exactly the same way as clinical data; for the centres involved in this work, most clinical studies involve the investigation of dementia. Realistic HMPAO SPECT simulation would have applications in (particularly multicentre) quality assurance (Heikkinen et al., 1998), assessment of the portability of normal databases and the optimisation of processing techniques through the use of lesions simulated in a normal distribution (Grova et al., 2003, Stamatakis et al., 1999, Ward et al., 2005).
Section snippets
Sandwich rCBF phantom
The basic design for the phantom was taken from Van Laere et al. (2002a). The phantom consists of 53 4 mm PMMA (polymethylmetacrylate, density 1.10 g cm− 3) discs of 200 mm outer diameter, kept together by four PMMA screw rods for compression of the radioactive sheets as well as the reproducible placement of the preformatted printer sheets (see Fig. 1).
rCBF activity distribution software templates
The SPM canonical single subject T1 template was used to create a software phantom for the creation of the stacked printout slices. SPM99 was used to
Two- and three-dimensional reproducibility of activity measurements
The average uniformity of the measured planar activity was 2.1 ± 0.7% (see 2.6). After correction for radioactive decay, the activity reproducibility for the planar phantom slice measurements was 2.1%. The reproducibility of reconstructed SPECT activity, assessed for each of the 19 VOIs listed in Table 2, was 1.1 ± 0.8%.
Comparison with normal database I: difference measure
The normalised mean square error was calculated for each of the subresolution phantom scans and for each of the 34 control scans. The results are given in Table 4 and as Fig. 4. It
Discussion
Results for uniformity and reproducibility of single printed sheets and the assembled phantom are in agreement with those reported by Larsson et al. (2000) and Van Laere et al. (2002a). This is unsurprising as similar printers were used in the previous work. More modern inkjet printers should give at least as good results with faster printing speeds. Although a relatively high level of radioactivity was used in the phantom in this development study, lower levels (up to a factor of 10) could be
References (39)
- et al.
Cingulate cortex hypoperfusion predicts Alzheimer's disease in mild cognitive impairment
BMC Neurol.
(2002) - et al.
Voxel- and VOI-based analysis of SPECT CBF in relation to clinical and psychological heterogeneity of mild cognitive impairment
Neuroimage
(2003) - et al.
Reducing between scanner differences in multi-center PET studies
Neuroimage
(2009) - et al.
Validation of the cerebellum as a reference region for SPECT quantification in patients suffering from dementia of the Alzheimer type
Psychiatry Res.
(1999) - et al.
Statistical parametric mapping of (99m)Tc-HMPAO-SPECT images for the diagnosis of Alzheimer's disease: normalizing to cerebellar tracer uptake
Neuroimage
(2002) - et al.
Using a white matter reference to remove the dependency of global signal on experimental conditions in SPECT analyses
Neuroimage
(2006) - et al.
Validation of statistical parametric mapping (SPM) in assessing cerebral lesions: a simulation study
Neuroimage
(1999) - et al.
Automated anatomical labeling of activations in SPM using a macroscopic anatomical parcellation of the MNI MRI single-subject brain
Neuroimage
(2002) - et al.
Experimental performance assessment of SPM for SPECT neuroactivation studies using a subresolution sandwich phantom design
Neuroimage
(2002) - et al.
Changes in brain functional homogeneity in subjects with Alzheimer's disease
Psychiatry Res.
(2002)
Data based optimization of brain SPECT processing for voxel-based statistical analysis
Optimisation of brain SPET and portability of normal databases
Eur. J. Nucl. Med. Mol. Imaging
Region of interest analysis using an SPM toolbox
The precuneus: a review of its functional anatomy and behavioural correlates
Brain
Principles and methods
A methodology for generating normal and pathological brain perfusion SPECT images for evaluation of MRI/SPECT fusion methods: application in epilepsy
Phys. Med. Biol.
Quality of brain perfusion single-photon emission tomography images: multicentre evaluation using an anatomically accurate three-dimensional phantom
Eur. J. Nucl. Med.
3-D phantom to simulate cerebral blood flow and metabolic images for PET
IEEE Trans. Nucl. Sci.
Tables of X-ray Mass Attenuation Coefficients and Mass Energy-Absorption Coefficients 1 keV to 20 MeV for Elements Z = 1 to 92 and 48 Additional Substances of Dosimetric Interest
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