CT-Based Attenuation Correction in I-123-Ioflupane SPECT

Purpose Attenuation correction (AC) based on low-dose computed tomography (CT) could be more accurate in brain single-photon emission computed tomography (SPECT) than the widely used Chang method, and, therefore, has the potential to improve both semi-quantitative analysis and visual image interpretation. The present study evaluated CT-based AC for dopamine transporter SPECT with I-123-ioflupane. Materials and methods Sixty-two consecutive patients in whom I-123-ioflupane SPECT including low-dose CT had been performed were recruited retrospectively at 3 centres. For each patient, 3 different SPECT images were reconstructed: without AC, with Chang AC and with CT-based AC. Distribution volume ratio (DVR) images were obtained by scaling voxel intensities using the whole brain without striata as reference. For assessing the impact of AC on semi-quantitative analysis, specific-to-background ratios (SBR) in caudate and putamen were obtained by fully automated SPM8-based region of interest (ROI) analysis and tested for their diagnostic power using receiver-operator- characteristic (ROC) analysis. For assessing the impact of AC on visual image reading, screenshots of stereotactically normalized DVR images presented in randomized order were interpreted independently by two raters at each centre. Results CT-based AC resulted in intermediate SBRs about half way between no AC and Chang. Maximum area under the ROC curve was achieved by the putamen SBR, with negligible impact of AC (0.924, 0.935 and 0.938 for no, CT-based and Chang AC). Diagnostic accuracy of visual interpretation also did not depend on AC. Conclusions The impact of CT-based versus Chang AC on the interpretation of I-123-ioflupane SPECT is negligible. Therefore, CT-based AC cannot be recommended for routine use in clinical patient care, not least because of the additional radiation exposure

CT-based attenuation correction in I-123-ioflupane SPECT.

PURPOSE: Attenuation correction (AC) based on low-dose computed tomography (CT) could be more accurate in brain single-photon emission computed tomography (SPECT) than the widely used Chang method, and, therefore, has the potential to improve both semi-quantitative analysis and visual image interpretation. The present study evaluated CT-based AC for dopamine transporter SPECT with I-123-ioflupane. MATERIALS AND METHODS: Sixty-two consecutive patients in whom I-123-ioflupane SPECT including low-dose CT had been performed were recruited retrospectively at 3 centres. For each patient, 3 different SPECT images were reconstructed: without AC, with Chang AC and with CT-based AC. Distribution volume ratio (DVR) images were obtained by scaling voxel intensities using the whole brain without striata as reference. For assessing the impact of AC on semi-quantitative analysis, specific-to-background ratios (SBR) in caudate and putamen were obtained by fully automated SPM8-based region of interest (ROI) analysis and tested for their diagnostic power using receiver-operator-characteristic (ROC) analysis. For assessing the impact of AC on visual image reading, screenshots of stereotactically normalized DVR images presented in randomized order were interpreted independently by two raters at each centre. RESULTS: CT-based AC resulted in intermediate SBRs about half way between no AC and Chang. Maximum area under the ROC curve was achieved by the putamen SBR, with negligible impact of AC (0.924, 0.935 and 0.938 for no, CT-based and Chang AC). Diagnostic accuracy of visual interpretation also did not depend on AC. CONCLUSIONS: The impact of CT-based versus Chang AC on the interpretation of I-123-ioflupane SPECT is negligible. Therefore, CT-based AC cannot be recommended for routine use in clinical patient care, not least because of the additional radiation exposure

Proposal for the standardisation of multi-centre trials in nuclear medicine imaging: prerequisites for a European 123I-FP-CIT SPECT database.

A framework has been designed to produce high-quality data for multi-centre SPECT studies. This framework has been successfully applied to a pan-European initiative to acquire a healthy control dopamine transporter image database

Results of the semi-quantitative analysis of the phantom studies.

<p>The specific-to-background ratio (SBR) was measured using the same whole striatum ROIs as in the patient studies (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0108328#pone-0108328-g001" target="_blank">Fig. 1</a>).</p>a<p>measured SBR: mean over left and right hemisphere.</p><p>Results of the semi-quantitative analysis of the phantom studies.</p

Bland-Altman plots comparing the SBR of the caudate (a) and the putamen (b) between CT-based and Chang AC (SBRs of both hemispheres were included independently, i.e. n = 124).

<p>Different scales were chosen for abscissae and ordinates in <b>a</b> and <b>b</b> for display purposes. The horizontal continuous line represents the mean difference, the dashed lines indicate the 95% confidence interval. The given p-value corresponds to the one-sample t-test for zero mean.</p

SPECT underestimates the true activity concentration in small structures such as the striatum and its substructures due to the limited spatial resolution in the reconstructed SPECT image (partial volume effect, PVE).

<p>In order to estimate the extent of underestimation in the present study, the reconstructed spatial resolution was estimated on the basis of a line source measurement using the same acquisition and reconstruction protocol as in the measurements of the striatal phantom and the patients included in the present study (no AC). Spatial resolution was found to be about 8 mm full-width-at-half-maximum (FWHM). Then a high-resolution CT of the striatal phantom was segmented manually (top row; from left to right: transversal, sagittal and coronal slice). Voxel values in the striatum were set to 6.5, voxel values in the background to 1.0 in order to simulate the actual SBR of about 5.5 in the phantom studies (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0108328#pone-0108328-t001" target="_blank">Table 1</a>). Then the segmented CT image was smoothed with a 3-dimensional Gaussian kernel with 8 mm FWHM to simulate the PVE in SPECT (bottom row). ROI analysis of the smoothed image resulted in a striatal SBR of 3.2 which underestimates the actual SBR of 5.5 by about 42%.</p

ROC curves for the differentiation between reduced and normal DAT availability by the SBR of the caudate (a) and the putamen (b) (minimum over both hemispheres).

<p>ROC curves for the differentiation between reduced and normal DAT availability by the SBR of the caudate (a) and the putamen (b) (minimum over both hemispheres).</p

Example page from the pdf document for visual scoring.

<p>The pdf document comprised one page for each I-123-ioflupane SPECT image showing a 12 mm thick slab (<b>a,</b><b>left</b>) and 4x4 slices of 4 mm thickness (<b>a,</b><b>right</b>). Example I-123-ioflupane SPECTs used as reference images for the visual scoring (<b>b</b>).</p

Proposal for the standardisation of multi-centre trials in nuclear medicine imaging: prerequisites for a European I-123-FP-CIT SPECT database

Purpose Multi-centre trials are an important part of proving the efficacy of procedures, drugs and interventions. Imaging components in such trials are becoming increasingly common; however, without sufficient control measures the usefulness of these data can be compromised. This paper describes a framework for performing high-quality multi-centre trials with single photon emission computed tomography (SPECT), using a pan-European initiative to acquire a normal control dopamine transporter brain scan database as an example.status: publishe