41 research outputs found
Entwicklung und Charakterisierung des MADPET4: Ein hochauflösend Kleintier-Positronen-Emissions-Tomographie-Insert für einen 7 T Magnetresonanztomographie-Scanner
No full textIn this work, the advantages of using individually read-out dual-layer crystals with high-gain SiPMs were studied in a small animal PET insert for a 7T MRI system. The PET insert offered high spatial resolution, high count rate capability, and high contrast recovery, with no compromise in PET ring thickness and sensitivity. MR-compatibility was studied for different imaging cases with three RF coil configurations and the insert was successfully tested in two simultaneous in-vivo mouse scans.In dieser Arbeit wurden die Vorteile der Anwendung individuell ausgelesener Doppelschichtkristalle und hochverstärkender SiPMs in einem Kleintier-PET-Insert für ein 7T-MRT-System untersucht. Das PET-Insert bietet hohe Auflösung, hohe Zählrate und hohe Kontrastwiederherstellung, ohne Einschränkungen bei PET-Ringdicke und -Empfindlichkeit. MR-Kompatibilität wurde für verschiedene Bildgebungsfälle mit drei HF-Spulenkonfigurationen untersucht und erfolgreich in zwei in-vivo Maus-Scans getestet
Sensitivity encoded silicon photomultiplier-a new sensor for high-resolution PET-MRI
No full textDetectors for simultaneous positron emission tomography and magnetic resonance imaging in particular with sub-mm spatial resolution are commonly composed of scintillator crystal arrays, readout via arrays of solid state sensors, such as avalanche photo diodes (APDs) or silicon photomultipliers (SiPMs). Usually a light guide between the crystals and the sensor is used to enable the identification of crystals which are smaller than the sensor elements. However, this complicates crystal identification at the gaps and edges of the sensor arrays. A solution is to use as many sensors as crystals with a direct coupling, which unfortunately increases the complexity and power consumption of the readout electronics. Since 1997, position-sensitive APDs have been successfully used to identify sub-mm crystals. Unfortunately, these devices show a limitation in their time resolution and a degradation of spatial resolution when placed in higher magnetic fields. To overcome these limitations, this paper presents a new sensor concept that extends conventional SiPMs by adding position information via the spatial encoding of the channel sensitivity. The concept allows a direct coupling of high-resolution crystal arrays to the sensor with a reduced amount of readout channels. The theory of sensitivity encoding is detailed and linked to compressed sensing to compute unique sparse solutions. Two devices have been designed using one- and two-dimensional linear sensitivity encoding with eight and four readout channels, respectively. Flood histograms of both devices show the capability to precisely identify all 4 × 4 LYSO crystals with dimensions of 0.93 × 0.93 × 10 mm3. For these crystals, the energy and time resolution (MV ± SD) of the devices with one (two)-dimensional encoding have been measured to be 12.3 (1 ± 0.047)% (13.7 (1 ± 0.047)%) around 511 keV with a paired coincidence time resolution (full width at half maximum) of 462 (1 ± 0.054) ps (452 (1 ± 0.078) ps)
Characterization of Sensitivity Encoded Silicon Photomultiplier (SeSP) with 1-Dimensional and 2-Dimensional Encoding for High Resolution PET/MR
No full textA 2D Sensitivity Encoded Silicon Photomultiplier (SeSP) for simultaneous high resolution PET/MR scanners
No full textIn this paper we present first results of a new detector concept called Sensitivity encoded Silicon Photomultiplier (SeSP) that has been invented in 2011. It combines the advantages of sensitivity encoding
and SiPM technology without changing the manufacturing process of the devices. We show the capability to accurately identify all 4×4
crystals of a regular array with 2×4 (1D-SeSP) and 2×2 (2D-SeSP) readout channels. Even for these initial realizations, good energy resolution (<13% (1D) and <15.5% (2D)), timing resolution (average CRT of 468ps @ FWHM, 2D-SeSP), and stable operation are achieved
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Dose Reduction in Pediatric Oncology Patients with Delayed Total-Body [18F]FDG PET/CT.
No full textOur aim was to define a lower limit of reduced injected activity in delayed [18F]FDG total-body (TB) PET/CT in pediatric oncology patients. Methods: In this single-center prospective study, children were scanned for 20 min with TB PET/CT, 120 min after intravenous administration of a 4.07 ± 0.49 MBq/kg dose of [18F]FDG. Five randomly subsampled low-count reconstructions were generated using ¼, ⅛, [Formula: see text], and [Formula: see text] of the counts in the full-dose list-mode reference standard acquisition (20 min), to simulate dose reduction. For the 2 lowest-count reconstructions, smoothing was applied. Background uptake was measured with volumes of interest placed on the ascending aorta, right liver lobe, and third lumbar vertebra body (L3). Tumor lesions were segmented using a 40% isocontour volume-of-interest approach. Signal-to-noise ratio, tumor-to-background ratio, and contrast-to-noise ratio were calculated. Three physicians identified malignant lesions independently and assessed the image quality using a 5-point Likert scale. Results: In total, 113 malignant lesions were identified in 18 patients, who met the inclusion criteria. Of these lesions, 87.6% were quantifiable. Liver SUVmean did not change significantly, whereas a lower signal-to-noise ratio was observed in all low-count reconstructions compared with the reference standard (P < 0.0001) because of higher noise rates. Tumor uptake (SUVmax), tumor-to-background ratio, and total lesion count were significantly lower in the reconstructions with [Formula: see text] and [Formula: see text] of the counts of the reference standard (P < 0.001). Contrast-to-noise ratio and clinical image quality were significantly lower in all low-count reconstructions than with the reference standard. Conclusion: Dose reduction for delayed [18F]FDG TB PET/CT imaging in children is possible without loss of image quality or lesion conspicuity. However, our results indicate that to maintain comparable tumor uptake and lesion conspicuity, PET centers should not reduce the injected [18F]FDG activity below 0.5 MBq/kg when using TB PET/CT in pediatric imaging at 120 min after injection
Lutetium background radiation in total-body PET-A simulation study on opportunities and challenges in PET attenuation correction.
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PET performance evaluation of MADPET4: a small animal PET insert for a 7 T MRI scanner.
No full textMADPET4 is the first small animal PET insert with two layers of individually read out crystals in combination with silicon photomultiplier technology. It has a novel detector arrangement, in which all crystals face the center of field of view transaxially. In this work, the PET performance of MADPET4 was evaluated and compared to other preclinical PET scanners using the NEMA NU 4 measurements, followed by imaging a mouse-size hot-rod resolution phantom and two in vivo simultaneous PET/MRI scans in a 7 T MRI scanner. The insert had a peak sensitivity of 0.49%, using an energy threshold of 350 keV. A uniform transaxial resolution was obtained up to 15 mm radial offset from the axial center, using filtered back-projection with single-slice rebinning. The measured average radial and tangential resolutions (FWHM) were 1.38 mm and 1.39 mm, respectively. The 1.2 mm rods were separable in the hot-rod phantom using an iterative image reconstruction algorithm. The scatter fraction was 7.3% and peak noise equivalent count rate was 15.5 kcps at 65.1 MBq of activity. The FDG uptake in a mouse heart and brain were visible in the two in vivo simultaneous PET/MRI scans without applying image corrections. In conclusion, the insert demonstrated a good overall performance and can be used for small animal multi-modal research applications
Improving depth-of-interaction resolution in pixellated PET detectors using neural networks
No full textParallax error is a common issue in high-resolution preclinical positron emission tomography (PET) scanners as well as in clinical scanners that have a long axial field of view (FOV), which increases estimation uncertainty of the annihilation position and therefore degrades the spatial resolution. A way to address this issue is depth-of-interaction (DOI) estimation. In this work we propose two machine learning-based algorithms, a dense and a convolutional neural network (NN), as well as a multiple linear regression (MLR)-based method to estimate DOI in depolished PET detector arrays with single-sided readout. The algorithms were tested on an 8× 8 array of 1.53× 1.53× 15 mm3 crystals and a 4× 4 array of 3.1× 3.1× 15 mm3 crystals, both made of Ce:LYSO scintillators and coupled to a 4× 4 array of 3× 3 mm3 silicon photomultipliers (SiPMs). Using the conventional linear DOI estimation method resulted in an average DOI resolution of 3.76 mm and 3.51 mm FWHM for the 8× 8 and the 4× 4 arrays, respectively. Application of MLR outperformed the conventional method with average DOI resolutions of 3.25 mm and 3.33 mm FWHM, respectively. Using the machine learning approaches further improved the DOI resolution, to an average DOI resolution of 2.99 mm and 3.14 mm FWHM, respectively, and additionally improved the uniformity of the DOI resolution in both arrays. Lastly, preliminary results obtained by using only a section of the crystal array for training showed that the NN-based methods could be used to reduce the number of calibration steps required for each detector array
MR-compatibility assessment of MADPET4: a study of interferences between an SiPM-based PET insert and a 7 T MRI system
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