Limits...
The Role of CT-Based Attenuation Correction and Collimator Blurring Correction in Striatal Spect Quantification.

Warwick JM, Rubow S, du Toit M, Beetge E, Carey P, Dupont P - Int J Mol Imaging (2011)

Bottom Line: Recovery values (phantom data) or average-specific uptake ratios (patient data) for the different reconstructions were compared at similar noise levels.Results.Conclusions.

View Article: PubMed Central - PubMed

Affiliation: Nuclear Medicine, Faculty of Health Sciences, Stellenbosch University and Tygerberg Hospital, Tygerberg, 7505, Cape Town, South Africa.

ABSTRACT
Purpose. Striatal single photon emission computed tomography (SPECT) imaging of the dopaminergic system is becoming increasingly used for clinical and research studies. The question about the value of nonuniform attenuation correction has become more relevant with the increasing availability of hybrid SPECT-CT scanners. In this study, the value of nonuniform attenuation correction and correction for collimator blurring were determined using both phantom data and patient data. Methods. SPECT imaging was performed using 7 anthropomorphic phantom measurements, and 14 patient studies using [I-123]-FP-CIT (DATSCAN). SPECT reconstruction was performed using uniform and nonuniform attenuation correction and collimator blurring corrections. Recovery values (phantom data) or average-specific uptake ratios (patient data) for the different reconstructions were compared at similar noise levels. Results. For the phantom data, improved recovery was found with nonuniform attenuation correction and collimator blurring corrections, with further improvement when performed together. However, for patient data the highest average specific uptake ratio was obtained using collimator blurring correction without nonuniform attenuation correction, probably due to subtle SPECT-CT misregistration. Conclusions. This study suggests that an optimal brain SPECT reconstruction (in terms of the lowest bias) in patients would include a correction for collimator blurring and uniform attenuation correction.

No MeSH data available.


Related in: MedlinePlus

Plot of average recovery (AR) for a single phantom study (using unsmoothed data) as a function of translational SPECT-CT mis-registration (perpendicular to the tomographic axis of rotation, 1 pixel = 2.95 mm) or rotational SPECT mis-registration (around the axis of the tomographic axis of rotation), (abbreviations: ct: nonuniform attenuation correction using a CT-based attenuation map; p0, pd: no, and depth dependent correction for collimator blurring, resp., based on the optimized method). The solid line gives the AR value calculated using uniform attenuation correction and depth dependent correction for collimator blurring.
© Copyright Policy - open-access
Related In: Results  -  Collection


getmorefigures.php?uid=PMC3094814&req=5

fig3: Plot of average recovery (AR) for a single phantom study (using unsmoothed data) as a function of translational SPECT-CT mis-registration (perpendicular to the tomographic axis of rotation, 1 pixel = 2.95 mm) or rotational SPECT mis-registration (around the axis of the tomographic axis of rotation), (abbreviations: ct: nonuniform attenuation correction using a CT-based attenuation map; p0, pd: no, and depth dependent correction for collimator blurring, resp., based on the optimized method). The solid line gives the AR value calculated using uniform attenuation correction and depth dependent correction for collimator blurring.

Mentions: Perhaps the most interesting findings of this study were the results obtained when nonuniform attenuation correction and collimator blurring corrections were used together. Intuitively, one would expect that this combination would result in a further increase in the average recovery and specific uptake ratio. This was indeed the case for the values obtained using the phantom data. The use of both correction methods resulted in an average recovery that was increased compared to the case when nonuniform attenuation correction alone was applied. This was also the case when a uniform attenuation correction was applied in combination with a collimator blurring correction. However, the findings for the patient data revealed a different result. For the patient studies, the highest average specific uptake ratio aSUR was achieved using collimator blurring corrections in combination with a uniform attenuation correction. The reason for this finding is not immediately clear; however the combination of patient data, nonuniform attenuation and collimator blurring corrections unexpectedly leads to a suboptimal result. It can be speculated that patient studies are likely to have small misregistrations between the SPECT and CT studies due to patient movement between the acquisitions, something that should not occur with a phantom study. These small mis-registrations may not have a major impact on reconstructions with nonuniform attenuation correction for the striatal regions but reconstructions with collimator blurring corrections may be more sensitive to them. Based on a visual assessment, there were no marked mis-registrations of the patient data used in this study, but it is possible, however, that there may be subtle differences, not seen with visual inspection. To further test this explanation, a single phantom study was taken and deliberate SPECT-CT translational and rotational mis-registrations were introduced. The mis-registered data were then reconstructed using uniform attenuation correction combined with a depth dependent collimator blurring correction, nonuniform attenuation correction alone, and nonuniform attenuation correction combined with a correction for collimator blurring. Rotational mis-registration up to 4 degrees was found to have little effect on striatal AR, but a translational mis-registration of 3–6 mm (1-2 pixels) gave a result similar to that obtained for the patient data above, that is, the highest recovery was obtained for reconstruction with a uniform attenuation correction and combined with a collimator blurring correction (Figure 3).


The Role of CT-Based Attenuation Correction and Collimator Blurring Correction in Striatal Spect Quantification.

Warwick JM, Rubow S, du Toit M, Beetge E, Carey P, Dupont P - Int J Mol Imaging (2011)

Plot of average recovery (AR) for a single phantom study (using unsmoothed data) as a function of translational SPECT-CT mis-registration (perpendicular to the tomographic axis of rotation, 1 pixel = 2.95 mm) or rotational SPECT mis-registration (around the axis of the tomographic axis of rotation), (abbreviations: ct: nonuniform attenuation correction using a CT-based attenuation map; p0, pd: no, and depth dependent correction for collimator blurring, resp., based on the optimized method). The solid line gives the AR value calculated using uniform attenuation correction and depth dependent correction for collimator blurring.
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3094814&req=5

fig3: Plot of average recovery (AR) for a single phantom study (using unsmoothed data) as a function of translational SPECT-CT mis-registration (perpendicular to the tomographic axis of rotation, 1 pixel = 2.95 mm) or rotational SPECT mis-registration (around the axis of the tomographic axis of rotation), (abbreviations: ct: nonuniform attenuation correction using a CT-based attenuation map; p0, pd: no, and depth dependent correction for collimator blurring, resp., based on the optimized method). The solid line gives the AR value calculated using uniform attenuation correction and depth dependent correction for collimator blurring.
Mentions: Perhaps the most interesting findings of this study were the results obtained when nonuniform attenuation correction and collimator blurring corrections were used together. Intuitively, one would expect that this combination would result in a further increase in the average recovery and specific uptake ratio. This was indeed the case for the values obtained using the phantom data. The use of both correction methods resulted in an average recovery that was increased compared to the case when nonuniform attenuation correction alone was applied. This was also the case when a uniform attenuation correction was applied in combination with a collimator blurring correction. However, the findings for the patient data revealed a different result. For the patient studies, the highest average specific uptake ratio aSUR was achieved using collimator blurring corrections in combination with a uniform attenuation correction. The reason for this finding is not immediately clear; however the combination of patient data, nonuniform attenuation and collimator blurring corrections unexpectedly leads to a suboptimal result. It can be speculated that patient studies are likely to have small misregistrations between the SPECT and CT studies due to patient movement between the acquisitions, something that should not occur with a phantom study. These small mis-registrations may not have a major impact on reconstructions with nonuniform attenuation correction for the striatal regions but reconstructions with collimator blurring corrections may be more sensitive to them. Based on a visual assessment, there were no marked mis-registrations of the patient data used in this study, but it is possible, however, that there may be subtle differences, not seen with visual inspection. To further test this explanation, a single phantom study was taken and deliberate SPECT-CT translational and rotational mis-registrations were introduced. The mis-registered data were then reconstructed using uniform attenuation correction combined with a depth dependent collimator blurring correction, nonuniform attenuation correction alone, and nonuniform attenuation correction combined with a correction for collimator blurring. Rotational mis-registration up to 4 degrees was found to have little effect on striatal AR, but a translational mis-registration of 3–6 mm (1-2 pixels) gave a result similar to that obtained for the patient data above, that is, the highest recovery was obtained for reconstruction with a uniform attenuation correction and combined with a collimator blurring correction (Figure 3).

Bottom Line: Recovery values (phantom data) or average-specific uptake ratios (patient data) for the different reconstructions were compared at similar noise levels.Results.Conclusions.

View Article: PubMed Central - PubMed

Affiliation: Nuclear Medicine, Faculty of Health Sciences, Stellenbosch University and Tygerberg Hospital, Tygerberg, 7505, Cape Town, South Africa.

ABSTRACT
Purpose. Striatal single photon emission computed tomography (SPECT) imaging of the dopaminergic system is becoming increasingly used for clinical and research studies. The question about the value of nonuniform attenuation correction has become more relevant with the increasing availability of hybrid SPECT-CT scanners. In this study, the value of nonuniform attenuation correction and correction for collimator blurring were determined using both phantom data and patient data. Methods. SPECT imaging was performed using 7 anthropomorphic phantom measurements, and 14 patient studies using [I-123]-FP-CIT (DATSCAN). SPECT reconstruction was performed using uniform and nonuniform attenuation correction and collimator blurring corrections. Recovery values (phantom data) or average-specific uptake ratios (patient data) for the different reconstructions were compared at similar noise levels. Results. For the phantom data, improved recovery was found with nonuniform attenuation correction and collimator blurring corrections, with further improvement when performed together. However, for patient data the highest average specific uptake ratio was obtained using collimator blurring correction without nonuniform attenuation correction, probably due to subtle SPECT-CT misregistration. Conclusions. This study suggests that an optimal brain SPECT reconstruction (in terms of the lowest bias) in patients would include a correction for collimator blurring and uniform attenuation correction.

No MeSH data available.


Related in: MedlinePlus