Valentino Bettinardi

Different neural systems for the recognition of animals and man-made tools

Using positron emission tomography, we mapped brain activity in normal volunteers during the recognition of visual stimuli representing living (animals) and nonliving (artefacts) entities. The subjects had to decide whether pairs of visual stimuli were different representations of the same object, or different objects. Animal recognition was associated with activations in the inferior temporo-occipital areas, bilaterally, whereas artefact recognition engaged a predominantly left hemispheric network, involving the left dorsolateral frontal cortex. These findings, which concur with clinical observations in neurological patients, provide in vivo evidence for a fractionation of the neural substrates of semantic knowledge in man.

Physical performance of the new hybrid PET∕CT Discovery-690.

PURPOSE The aim of this work was the assessment of the physical performance of the new hybrid PET∕CT system: Discovery-690. METHODS The Discovery-690 combines a lutetium-yttrium-orthosilicate (LYSO) block detector designed PET tomograph with a 64-slice CT scanner. The system is further characterized by a dedicated powerful computing platform implementing fully 3D-PET iterative reconstruction algorithms. These algorithms can account for time of flight (TOF) information and∕or a 3D model of the PET point spread function (PSF). PET physical performance was measured following NEMA NU-2-2007 procedures. Furthermore, specific tests were used: (i) to measure the energy and timing resolution of the PET system and (ii) to evaluate image quality, by using phantoms representing different clinical conditions (e.g., brain and whole body). Data processing and reconstructions were performed as required by standard procedures. Further reconstructions were carried out to evaluate the performance of the new reconstruction algorithms. In particular, four algorithms were considered for the reconstruction of the PET data: (i) HD = standard configuration, without TOF and PSF, (ii) TOF = HD + TOF, (iii) PSF = HD + PSF, and (iv) TOFPSF = HD + TOF + PSF. RESULTS The transverse (axial) spatial resolution values were 4.70 (4.74) mm and 5.06 (5.55) mm at 1 cm and 10 cm off axis, respectively. Sensitivity (average between 0 and 10 cm) was 7.5 cps∕kBq. The noise equivalent count rate (NECR) peak was 139.1 kcps at 29.0 kBq∕ml. The scatter fraction at the NECR peak was 37%. The correction accuracy for the dead time losses and random event counts had a maximum absolute error below the NECR peak of 2.09%. The average energy and timing resolution were 12.4% and 544.3 ps, respectively. PET image quality was evaluated with the NEMA IEC Body phantom by using four reconstruction algorithms (HD, TOF, PSF, and TOFPSF), as previously described. The hot contrast (after 3 iterations and for a lesion∕background activity ratio of 4:1) for the spheres of 10, 13, 17, and 22 mm was (HD) 29.8, 45.4, 55.4, and 68.1%; (TOF) 39.9, 53.5, 62.7, and 72.2%; (PSF) 28.3, 47.3, 60.4, and 71.8%; (TOFPSF) 43.8, 62.9, 70.6, and 76.4%. The cold contrast for the spheres of 28 and 37 mm was (HD) 62.4 and 65.2%; (TOF) 77.1 and 81.4%; (PSF) 62.0 and 65.2%; (TOFPSF) 77.3 and 81.6%. Similar hot and cold contrast trends were found during the analyses of other phantoms representing different clinical conditions (brain and whole body). Nevertheless, the authors observed a predominant role of either TOF or PSF, depending on the specific characteristics and dimensions of the phantoms. CONCLUSIONS Discovery-690 shows very good PET physical performance for all the standard NEMA NU-2-2007 measurements. Furthermore, the new reconstruction algorithms available for PET data (TOF and PSF) allow further improvements of the D-690 image quality performance both qualitatively and quantitatively.

Value of integrated PET/CT for lesion localisation in cancer patients: a comparative study

The aim of this study was to retrospectively compare the value of integrated PET/CT and separate PET plus morphological imaging studies for lesion localisation in cancer patients. Two different series of consecutive patients who had previously been treated for neoplastic disease were considered. One series consisted of 105 patients who had undergone [18F]fluorodeoxyglucose (FDG) PET/CT (n=70) or [11C]choline PET/CT (n=35) studies (PET/CT group). The other series comprised 105 patients who had undergone FDG PET scan (n=70) or [11C]choline PET scan (n=35) alone; in this series, PET findings were correlated with the results of morphological imaging (MI) studies, i.e. CT (n=92) or MR imaging (n=13) (PET+MI group). Regions of abnormal tracer uptake at PET scanning were classified as ambiguous or unambiguous depending on their precise anatomical localisation. A total of 207 and 196 lesions were found in the PET/CT and PET+MI groups, respectively. The difference in terms of number of lesions per patient detected with the two imaging protocols was not statistically significant (P=0.718). When analysis of lesion localisation was performed, there were 7/207 (3.4%) and 30/196 (15.3%) ambiguous lesions in the PET/CT and PET+MI groups, respectively. The number of ambiguous lesions was significantly higher in the PET+MI group than in the PET/CT group (χ2=15.768, P<0.0001). Comparison of the effect of use of the different tracers on reporting of PET/CT versus PET+MI revealed that the improvement in the final report in [11C]choline PET/CT studies was similar to that observed in [18F]FDG studies. In cancer patients, PET/CT shows higher diagnostic accuracy for lesion localisation than PET plus morphological imaging studies performed independently. This result does not seem to be affected by the type of tracer used.

Image-based point spread function implementation in a fully 3D OSEM reconstruction algorithm for PET

The interest in positron emission tomography (PET) and particularly in hybrid integrated PET/CT systems has significantly increased in the last few years due to the improved quality of the obtained images. Nevertheless, one of the most important limits of the PET imaging technique is still its poor spatial resolution due to several physical factors originating both at the emission (e.g. positron range, photon non-collinearity) and at detection levels (e.g. scatter inside the scintillating crystals, finite dimensions of the crystals and depth of interaction). To improve the spatial resolution of the images, a possible way consists of measuring the point spread function (PSF) of the system and then accounting for it inside the reconstruction algorithm. In this work, the system response of the GE Discovery STE operating in 3D mode has been characterized by acquiring (22)Na point sources in different positions of the scanner field of view. An image-based model of the PSF was then obtained by fitting asymmetric two-dimensional Gaussians on the (22)Na images reconstructed with small pixel sizes. The PSF was then incorporated, at the image level, in a three-dimensional ordered subset maximum likelihood expectation maximization (OS-MLEM) reconstruction algorithm. A qualitative and quantitative validation of the algorithm accounting for the PSF has been performed on phantom and clinical data, showing improved spatial resolution, higher contrast and lower noise compared with the corresponding images obtained using the standard OS-MLEM algorithm.

Activation of precentral and mesial motor areas during the execution of elementary proximal and distal arm movements: a Pet study

Regional cerebral blood flow was measured using positron emission tomography (PET) in normal subjects while performing simple aimless proximal and distal arm movements. The aim of the experiment was to compare the somatotopic organization of precentral and mesial (the so called supplementary motor area, SMA) motor cortices and to evaluate whether in man, as in the monkey, the rostral and caudal sectors of SMA are functionally different. The results showed that proximal and distal arm movements are to a large extent segregated in the precentral motor cortex, but not in the SMA. They also showed that the SMA is made of at least two functional sectors. Only the caudal one is activated during simple aimless movements.

Integrated PET/CT as a first-line re-staging modality in patients with suspected recurrence of ovarian cancer

PurposeThe aims of this study were to compare CT with PET/CT results in patients with suspected ovarian cancer recurrence and to assess the impact of the PET/CT findings on their clinical management.MethodsThirty-two consecutive patients with suspected ovarian cancer recurrence were retrospectively included in the study. Abdominal contrast-enhanced CT and PET/CT with [18F]FDG, in addition to conventional follow-up, were performed in all 32 patients. After the comparison between CT and PET/CT results, based on clinical reports, changes in the clinical management of patients (intermodality changes) due to PET/CT information were analysed.ResultsTwenty of the 32 patients were positive at CT (62.5%) versus 29 (90.6%) at PET/CT. Intermodality changes in management, i.e. use of a different treatment modality, after PET/CT examination were indicated in 14/32 (44%) patients. In particular, before PET/CT study, the planned management was as follows: wait-and-see in 7/32 (22%), further instrumental examinations in 4/32 (12%), chemotherapy in 10/32 (31%), diagnostic surgical treatment in 6/32 (19%) and surgical treatment in the remaining 5/32 (16%). After PET/CT study, wait-and-see was indicated in 1/32 (3%), further instrumental examinations in 7/32 (22%), chemotherapy in 16/32 (50%), diagnostic surgical treatment in 2/32 (6%) and surgical treatment in the remaining 6/32 (19%).ConclusionIntegrated PET/CT could detect tumour relapse in a higher percentage of patients than could CT. A change in the clinical management was observed in 44% of cases when PET/CT information was added to conventional follow-up findings.

Detection and compensation of organ/lesion motion using 4D-PET/CT respiratory gated acquisition techniques

PURPOSE To describe the degradation effects produced by respiratory organ and lesion motion on PET/CT images and to define the role of respiratory gated (RG) 4D-PET/CT techniques to compensate for such effects. METHODS Based on the literature and on our own experience, technical recommendations and clinical indications for the use of RG 4D PET/CT have been outlined. RESULTS RG 4D-PET/CT techniques require a state of the art PET/CT scanner, a respiratory monitoring system and dedicated acquisition and processing protocols. Patient training is particularly important to obtain a regular breathing pattern. An adequate number of phases has to be selected to balance motion compensation and statistical noise. RG 4D PET/CT motion free images may be clinically useful for tumour tissue characterization, monitoring patient treatment and target definition in radiation therapy planning. CONCLUSIONS RG 4D PET/CT is a valuable tool to improve image quality and quantitative accuracy and to assess and measure organ and lesion motion for radiotherapy planning.

Scatter correction techniques in 3D PET: a Monte Carlo evaluation

In this work a Monte Carlo software package, PET-EGS, designed to simulate realistic PET clinical studies, was used to assess three different approaches to scatter correction in 3D PET: analytical (gaussian fitting technique), experimental (dual energy window technique), probabilistic (Monte Carlo technique). Phantom and clinical studies were performed by 3D PET and simulated by PET-EGS. Clinical studies were simulated assuming PET emission/transmission multivolume images as voxelized source objects describing the distribution of both the radioactivity and attenuation coefficients and accounting for out-of-field activity and media. The accuracy of PET-EGS in modeling the physical response of a 3D PET scanner was assessed by statistical comparison between measured and total (scatter+unscatter) simulated distributions (probability for the two distributions to be the same distribution: p>0.95). The accuracy of the scatter models, for each scatter correction technique, was evaluated on sinograms by statistical comparison between the estimated and the simulated scatter distributions (agreement <1 /spl sigma/). The accuracy of scatter correction was evaluated on sinograms by comparison between scatter corrected and simulated unscatter distributions (residual scatter fraction <13 %).

Head holder for PET, CT, and MR studies

A new head holder for the fixation and repositioning of the patient head in PET, CT, and MR scanners has been designed and tested. With this device, a bidimensional correlation between functional and anatomical brain images can also be obtained. Head fixation and repositioning are achieved using the patients dental morphology as an anatomical reference. With a dentistic material, a mold of the patients teeth is obtained in a few minutes. The molding substance rests on a plastic support, fixed to the head holder. Each time the patient undergoes a new study, his/her personal mold is used, ensuring accurate head repositioning. External markers fixed on the head holder (made visible in lateral PET and CT projection images, midsaggital MR images, and also on the axial images) make it possible to record and recognize the angular orientation and the position of the brain in the three-dimensional space, to correlate images of the same patient obtained with different neuroimaging modalities, and to accurately reposition patients for follow-up studies. The head holder was tested on several subjects. Fixation and repositioning accuracy of within 2.5 mm were achieved in the three-dimensional space. Orientation accuracy was 1 degree.

Differentiation of clinically non-functioning pituitary adenomas from meningiomas and craniopharyngiomas by positron emission tomography with [18F]fluoro-ethyl-spiperone

The differential diagnosis among various types of non-functioning sellar and parasellar tumours is sometimes difficult using currently available methods of morphological imaging. The aim of this study was to define whether assessment of the uptake of [18F]fluoro-ethyl-spiperone (FESP) with positron emission tomography (PET) could be helpful for the differential diagnosis of pituitary adenomas and other parasellar lesions, and for establishing the appropriate therapeutic approach. The population examined comprised 16 patients with the diagnosis of primary tumour of the sellar/parasellar region who were waiting to undergo surgical treatment. The results demonstrated that PET with [18F]FESP is a very specific method for differentiating adenomas from craniopharyngiomas and meningiomas. The visual interpretation of images allows such differentiation at approximately 70 min after tracer injection. Semiquantitative analysis of the dynamic PET data confirmed the results of visual interpretation, demonstrating that the uptake of [18F]FESP was consistently (i.e. throughout the series) at least two- to threefold higher in non-functioning adenomas than in other parasellar tumours as early as 70 min after tracer injection, and that it increased still further thereafter. It is concluded that PET with [18F]FESP might be of clinical value in those cases in which the differential diagnosis among various histological types of sellar tumour is uncertain with conventional methods.