Is choline PET useful for identifying intraprostatic tumour lesions? A literature review.

More than 80% of patients with intermediate-risk or high-risk localized prostate cancer are cured with radiation doses of 74-78 Gy, but high doses increase the risk for late bowel and bladder toxicity among long-term survivors. Dose painting, defined as dose escalation to areas in the prostate containing the tumour, rather than to the whole gland, minimizes dose to normal tissues and hence toxicity. It requires accurate identification of the location and size of these lesions, for which functional MRI is the current gold standard. Many studies have assessed the use of choline PET in staging newly diagnosed patients. This review will discuss important imaging variables affecting the accuracy of choline PET scans, how choline PET contributes to tumour identification and is used in radiotherapy planning and how PET can improve the patient pathway involving prostate radiotherapy. In summary, the available literature shows that the accuracy of choline PET improves with higher tracer doses and delayed imaging (although the optimal uptake time is unclear), and tumour identification by MRI is improved by the addition of PET imaging. We propose future research with prolonged choline uptake time and multiphase imaging, which may further improve accuracy.

Experimental results from a prototype slit-slat collimator with mixed multiplexed and non-multiplexed data.

We have previously shown with simulations that a gain in signal-to-noise ratio (SNR) can be obtained by using mixed multiplexed (MX) and non-MX data in a slit-slat SPECT system as compared to using non-MX data only. We have now developed a prototype slit-slat collimator for a conventional gamma camera in order to validate these simulation results. The prototype collimator consists of seven slits and multiple parallel slats. Image reconstruction is performed using a modified OSEM algorithm, which takes into account geometric sensitivity variations and attenuation, but not scatter or resolution effects. Here, we first describe the calibration of the system and then we present the experimental validation with phantom experiments. SPECT acquisitions using different geometric and anthropomorphic phantoms were performed with and without multiplexing. The results show that reconstruction of the MX projections with the non-MX-projections eliminates artefacts caused by multiplexing. SNR gains obtained using the mixed MX and non-MX configurations were in the range of 26% to 51% for different phantoms. The results were in agreement with our previously published simulation work, proving that combining MX and non-MX data can result in artefact-free reconstructed images with improved SNR.

The potential for mixed multiplexed and non-multiplexed data to improve the reconstruction quality of a multi-slit-slat collimator SPECT system.

Multiplexing is a way of increasing the sensitivity in a multi-slit-slat SPECT system by allowing the overlap of projections from neighboring apertures. The fundamental objective of multiplexing is to increase the signal-to-noise ratio for a given system resolution. Multiplexing may therefore lead to an improved tradeoff between resolution and sensitivity. Overlapped projections, however, introduce ambiguities in the data which can lead to non-uniqueness of solution for the inverse problem, deterioration in the quality of reconstruction and ultimately loss of resolution. Therefore, it is not straightforward to evaluate the advantage of the extra sensitivity gained by multiplexing, without first devising a method to overcome the image artifacts caused due to this overlapping of projection data. In this paper we investigate the effect of multiplexing on the reconstructed image quality and we determine whether reconstruction of multiplexed data could be improved by the addition of non-multiplexed data. For this purpose we have done simulations based on three digital phantoms. We compared the reconstructed images both qualitatively and quantitatively for different degrees of multiplexing and different fractions of non-multiplexed data. Our results indicate that the recovery coefficient (and therefore spatial resolution) can be maintained with a high degree of multiplexing leading to a significant increase in the SNR (up to 25%) due to a reduced noise level. This gain in the SNR corresponds to a 75% increase in counts or sensitivity which can be utilized to reduce acquisition time, patient dose or/and improve image quality.