In nuclear medicine, the gamma-camera is one of the most used imaging devices for radionuclide imaging. Gamma-cameras are the key point of many devices used in nuclear medicine ranging from the scintigraphic system to SPECT (Single photon emission computed tomography) system. The main aim of a gamma-camera is to provide to the physician useful information in terms of spatial resolution and sensitivity of the organ under investigation. So, starting from previous studies where the AM (Additive manufacturing) technologies have been applied for the realization of collimators, we proceeded providing a novel concept of a parallel hole collimator with optimized hole shape and with a completely novel fabrication strategy printing the negative of the traditional collimator. With "negative geometry" we mean extruding the holes, usually empty, and filling then the space between these holes with a high dense metal powder (eg. Tungsten). Applying this concept, we found to be able to provide a fully customizable and low-cost product using traditional FDM (Fused deposition modeling) and SLS (Selective laser sintering) printing technologies. Two different geometries, for a total of six samples, have been 3D printed. These samples have been then filled by hand-filling process with tungsten powder and have been scanned, using CT scanner, in order to evaluate how the powder is dispersed between the septa. An imaging system used to acquire the printing process has been also mounted on-board of the FDM printer and it has been used to acquire a picture of each printed layer while being illuminated by three laser-line illuminators working in the 630 nm range (red illuminators). Laser illuminators have been placed to provide the best and constant illumination conditions on the imaged layer. Images have been post-processed and used to recreate a 3D model of the printed part to be then used in the simulation software GATE. A numerical analysis, based on GATE Monte Carlo toolkit, has been conducted to simulate the reference and the innovative concepts collimators. The simulations have been done using different radio-isotopes (Tc99, Lu177, In111 and Ga67) and materials (Tungsten, PLA and PA2200). Experimentally, the sample have been proved, mostly with the Tc99m source, to confirm the validity of the proposed idea. Results of the numerical analysis show a similar behavior for what concern the spatial resolution with the respective reference collimators, while for the sensitivity a reduction that range from 45% up to 80% of entries is reported. This is due mainly to the extruded pixel, made of PLA or PA2200, having higher density (~1.24 g/cc for PLA and ~0,95 g/cc for PA2200) with respect to air (~0,0012 g/cc). The 3D reconstructed model using the imaging system has been numerically evaluated as well. Demonstrating that the additive process errors, such as non-linearity and non-parallelism between the extruded holes, can have a worsening effect on the system performance. For future application further implementations are needed, especially for what concern the filling procedure that must be improved in order to reach an higher percentage of filled powder.
In medicina nucleare, la gamma-camera è uno dei dispositivi di imaging più utilizzati per l'imaging dei radionuclidi. Le gamma-camere sono il cuore di molti dispositivi utilizzati in medicina nucleare che vanno dal sistema scintigrafico al sistema SPECT (Tomografia computerizzata a emissione di singolo fotone). Lo scopo principale di una gamma-camera è fornire al medico informazioni utili in termini di risoluzione spaziale e sensibilità per l’organo sotto indagine. Quindi, partendo da studi precedenti in cui sono state applicate le tecnologie AM (Additive manufacturing) per la realizzazione di collimatori, si è proceduto fornendo un nuovo concetto di collimatore a fori paralleli con forma del foro ottimizzata e con una strategia di fabbricazione completamente innovativa stampando il negativo del collimatore tradizionale. Con "geometria negativa" si intende estrudere i fori, solitamente vuoti, e riempire poi lo spazio tra questi fori con una polvere metallica ad alta densità (es. tungsteno). Applicando questo concetto, abbiamo scoperto di essere in grado di fornire un prodotto completamente personalizzabile e a basso costo utilizzando le tradizionali tecnologie di stampa FDM (modellazione a deposizione fusa) e SLS (sinterizzazione laser selettiva). Sono state stampate in 3D due diverse geometrie, per un totale di sei campioni. Questi campioni sono stati poi riempiti a mano con polvere di tungsteno e sono stati scansionati, mediante scanner CT, al fine di valutare come la polvere fosse dispersa tra i setti. A bordo della stampante FDM è stato anche montato un sistema di imaging utilizzato per acquisire il processo di stampa ed è stato utilizzato per acquisire un'immagine di ogni singolo strato stampato illuminato da tre illuminatori a linea laser, che lavorano nella gamma di 630 nm (illuminatori rossi). Gli illuminatori laser sono stati posizionati per fornire le condizioni di illuminazione migliori e costanti sullo strato sottoposto ad imaging. Le immagini sono state post-elaborate e utilizzate per ricreare un modello 3D della parte stampata da utilizzare poi nel software di simulazione GATE. È stata condotta un'analisi numerica, basata sul toolkit GATE Monte Carlo, per simulare i collimatori di riferimento e concetti innovativi. Le simulazioni sono state effettuate utilizzando diversi radioisotopi (Tc99, Lu177, In111 e Ga67) e materiali (Tungsteno, PLA e PA2200). Sperimentalmente, il campione è stato testato principalmente con la sorgente Tc99m, per confermare la validità dell'idea proposta. I risultati dell'analisi numerica mostrano un comportamento simile per quanto riguarda la risoluzione spaziale con i rispettivi collimatori di riferimento, mentre per la sensibilità si riporta una riduzione che va dal 45% fino all'80% delle entries. Ciò è dovuto principalmente al pixel estruso, realizzato in PLA o PA2200, avente densità maggiore (~1,24 g/cc per PLA e ~0,95 g/cc per PA2200) rispetto all'aria (~0,0012 g/cc) . Anche il modello ricostruito in 3D utilizzando il sistema di imaging è stato valutato numericamente. Dimostrando che gli errori del processo additivo, come non linearità e non parallelismo tra i fori estrusi, possono avere un effetto peggiorativo sulle prestazioni del sistema. Per applicazioni future sono necessarie ulteriori implementazioni, specialmente per quanto riguarda la procedura di riempimento che deve essere migliorata per raggiungere una maggiore percentuale di polvere depositata.
Innovative 3D-printed gamma-camera collimators for medical imaging / Verdenelli, Lorenzo. - (2022 Mar 21).
Innovative 3D-printed gamma-camera collimators for medical imaging
VERDENELLI, LORENZO
2022-03-21
Abstract
In nuclear medicine, the gamma-camera is one of the most used imaging devices for radionuclide imaging. Gamma-cameras are the key point of many devices used in nuclear medicine ranging from the scintigraphic system to SPECT (Single photon emission computed tomography) system. The main aim of a gamma-camera is to provide to the physician useful information in terms of spatial resolution and sensitivity of the organ under investigation. So, starting from previous studies where the AM (Additive manufacturing) technologies have been applied for the realization of collimators, we proceeded providing a novel concept of a parallel hole collimator with optimized hole shape and with a completely novel fabrication strategy printing the negative of the traditional collimator. With "negative geometry" we mean extruding the holes, usually empty, and filling then the space between these holes with a high dense metal powder (eg. Tungsten). Applying this concept, we found to be able to provide a fully customizable and low-cost product using traditional FDM (Fused deposition modeling) and SLS (Selective laser sintering) printing technologies. Two different geometries, for a total of six samples, have been 3D printed. These samples have been then filled by hand-filling process with tungsten powder and have been scanned, using CT scanner, in order to evaluate how the powder is dispersed between the septa. An imaging system used to acquire the printing process has been also mounted on-board of the FDM printer and it has been used to acquire a picture of each printed layer while being illuminated by three laser-line illuminators working in the 630 nm range (red illuminators). Laser illuminators have been placed to provide the best and constant illumination conditions on the imaged layer. Images have been post-processed and used to recreate a 3D model of the printed part to be then used in the simulation software GATE. A numerical analysis, based on GATE Monte Carlo toolkit, has been conducted to simulate the reference and the innovative concepts collimators. The simulations have been done using different radio-isotopes (Tc99, Lu177, In111 and Ga67) and materials (Tungsten, PLA and PA2200). Experimentally, the sample have been proved, mostly with the Tc99m source, to confirm the validity of the proposed idea. Results of the numerical analysis show a similar behavior for what concern the spatial resolution with the respective reference collimators, while for the sensitivity a reduction that range from 45% up to 80% of entries is reported. This is due mainly to the extruded pixel, made of PLA or PA2200, having higher density (~1.24 g/cc for PLA and ~0,95 g/cc for PA2200) with respect to air (~0,0012 g/cc). The 3D reconstructed model using the imaging system has been numerically evaluated as well. Demonstrating that the additive process errors, such as non-linearity and non-parallelism between the extruded holes, can have a worsening effect on the system performance. For future application further implementations are needed, especially for what concern the filling procedure that must be improved in order to reach an higher percentage of filled powder.File | Dimensione | Formato | |
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Open Access dal 22/09/2023
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