H. du Raan

Production of radioactive quality assurance phantoms using a standard inkjet printer.

This note proposes the use of a standard inkjet printer to produce radioactive 99mTc phantoms that can be used for routine quality control of gamma cameras. The amount of activity that will be deposited on paper per unit area was predicted and compared to the measured activity. The uniformity of the printouts was compared to the uniformity obtained with a standard 57Co flood source. A scintillation detector connected to a multi-channel analyzer was used to evaluate the uniformity of the printout independently from the gamma camera. Joining two A4 size printed phantoms to create larger sources was evaluated. The spatial resolution obtained with printed sources was compared to that obtained using standard line source techniques. The results indicated that the uniformity of the printed phantoms compared well with those obtained with the 57Co flood source (integral uniformity 2.29% (printed source) and 2.10% (57Co flood source)). There was no difference in the resolution measurements obtained with the printed sources and those obtained with the standard methods. This study demonstrates that affordable phantoms can easily be created to evaluate system uniformity and resolution in any department where a standard PC and inkjet printer are available.

Implementation of a Tc-99m and Ce-139 scanning line source for attenuation correction in SPECT using a dual opposing detector scintillation camera

Image degradation during single photon emission computed tomography (SPECT) due to attenuation and Compton scatter of photons can cause clinical image artifacts and will also result in inaccurate quantitative data. Therefore attenuation correction methods recently received wide interest. Transmission imaging can be performed to obtain the attenuation coefficients of a nonhomogeneous attenuating medium accurately. The aim of this study was firstly to evaluate the imaging characteristics of the scanning line source assembly. The results obtained with Tc-99m and Ce-139 were compared. Secondly the calculated attenuation coefficients were compared with known values from literature, using Tc-99m and Ce-139 as transmission sources. Lastly the method of acquiring simultaneous transmission and emission data was investigated. This study shows that an attenuation coefficient map can be obtained using a scanning line source for transmission imaging with a dual opposing detector camera. The imaging characteristics of Tc-99m and Ce-139 as transmission sources are similar. The resolution obtained with the Ce-139 line source was poorer than that obtained with the Tc-99m line source. A linear relationship was found between CT numbers and attenuation coefficients for transmission images using both Tc-99m and Ce-139 line sources. The attenuation coefficient value for water was underestimated by 1% using the Tc-99m transmission source and underestimated by 10% using Ce-139 as transmission source. This underestimation of attenuation coefficient values was also obtained in the human study. A myocardial perfusion study processed without and with attenuation correction clearly demonstrated the effect of the attenuation correction in the inferior myocardial region. The potential of using a scanning line source as transmission source with a dual opposing detector camera has been demonstrated in this study. The transmission source, Ce-139 was successfully introduced in this investigation for simultaneous acquisition of transmission and emission data.

Evaluation of an uncollimated printed paper transmission source used under scatter limiting conditions

Transmission sources used for image attenuation correction, allowing image quantification, are collimated to reduce scatter. We propose the same effect can be achieved for an uncollimated source by increasing source to patient distance. The aim was to compare planar image performance characteristics and absorbed doses of uncollimated and collimated radioactive printed paper transmission sources. The scatter contribution to the uncollimated (⁹⁹m)Tc source data was evaluated for different combinations of detector phantom distance, detector source distance and phantom source distance. Measurements were performed by increasing the Lucite phantom thickness in 1cm steps to 20 cm. Spatial resolution, detection efficiency and entrance absorbed dose rate were measured for the uncollimated and collimated transmission source images. Results derived from the energy spectra, obtained with the uncollimated transmission source indicate that scatter contribution increases with decreasing detector source distance. The scatter component in the uncollimated transmission images (detector source distances ≥ 60 cm; phantom source distances ≥ 40 cm) was comparable to that obtained with collimated transmission images. Attenuation coefficients obtained compared well (0.168 cm⁻¹ vs. 0.171 cm⁻¹). The full widths at half maxima differed by less than 0.9 mm. The detection efficiency of the uncollimated source was 2.5 times higher than obtained with the collimated source. The entrance absorbed dose obtained from an uncollimated source was 3.75 times larger than that obtained from the collimated source. An uncollimated transmission source (detector source distance ≥ 60 cm) results in acceptable image characteristics and presents a low cost, low dose, high efficiency option for transmission imaging.

O.12 - Determination of the influence of respiratory motion on the SUV accuracy in pulmonary lesions

Introduction and Aim: Respiratory motion results in reduction of qualitative and quantitative accuracy in PET imaging of the heart, muscles of the diaphragm, liver, spleen, pancreas and imaging of the lung area. It causes blurring of the images and thus a loss of sensitivity in lesion detection. The aim was to determine the importance of respiratory motion on SUV accuracy in pulmonary lesions through simulation of respiratory motion. Materials and Methods: The XCAT Phantom was used to assess the influence of breathing on SUV quantification in a human-like simulation model. Six spherical lesions were introduced into the lungs of the model, three in the left lung and three in the right lung. Activity concentrations assigned to the lesions were varied to create a range of different lesions: background ratios, thus creating a range of contrasts. The simulations were repeated for various lesion sizes. GATE software was used to performMonte Carlo simulations during breathing. True-, scattered-, randomand total coincidences were extracted from the simulated data and reconstructed using OPL-EM and corrected for attenuation. Results: The % trues-to-total coincidences generally followed a downward trend with a decrease in contrast. Scattered coincidences had a more significant contribution at low contrast and when the lesion was closer to the diaphragm. This was greater in 3D simulations than in 2D simulations. Random coincidences were relatively greater in the apical region than in the other lung regions, particularly at low contrast large lesions. This increased for 3D compared to 2D acquisitions. The fraction of true coincidences-to-total coincidences increased when the lesions became smaller, but the relative amount of scattered events also increased. Conclusion: Breathing plays a significant role when determining the SUV of pulmonary lesions after accounting for the size, location, and the amount of activity within the simulated lesions compared to the background activity.

Evaluation of Two Scatter Corrections Techniques for an Uncollimated Transmission Flood Source

Scattered photons can be a problem in transmission computed tomography (TCT) when employing an uncollimated transmission source. As an uncollimated transmission source can generate many scatter events in the transmission data, accurate scatter correction is necessary during transmission imaging. The aim of this study was to evaluate two scatter correction techniques which can be used with an uncollimated flood source for transmission imaging.