In modern computed tomography (CT) scanners, automatic tube current modulation (ATCM) adapts exposure parameters to patient size based on two-dimensional (frontal and/or lateral) pre-scan images, known as localizers, in order to achieve consistent image quality across the diversity of patient body sizes. However, clinical radiation dose and image quality data exhibit variability even across comparable body habitus, and with the same CT scanner. A potential cause of this variability could be associated with patient positioning, since localizers may be affected by both patient vertical off-centering and the position of patient extremities. A clinical study to determine the sources of this variability is unfeasible because it would involve repeatedly imaging the same patient. Therefore, a virtual imaging trial (VIT) was designed to evaluate how clinical data inconsistencies are related to TCM’s capability to adapt to different patient body habitus and positioning with respect to the isocenter. Three virtual patients (XCAT) representing different body habitus (BMIs: 24.4, 28.5, 32.2 kg/m2) were imaged with a Siemens SOMATOM Definition Flash CT scanner simulator (DukeSim), using a clinical chest-abdomen protocol. Each patient was scanned under six different conditions: with arms above the head at the isocenter (standard position) and at various vertical offsets (-80, -40, -20; +40 mm); and with arms alongside the trunk at the isocenter. CTDIvol, organ dose (esophagus, lungs, liver, stomach, spleen, intestine, pancreas, kidneys, gallbladder), global noise index (GNI) in soft tissues and specific organs (lungs and liver), and water equivalent diameter (WED) were calculated and compared as percentage differences relative to the corresponding standard position values. For vertical shifts, the percentage difference for the three patients reached values up to 2.3 ± 0.8% for CTDIvol, 13.1 ± 0.5% for soft tissue GNI, 21.8 ± 0.5% for lungs GNI, 13 ± 1% for liver GNI, and -0.1566 ± 0.0006% for WED. Percentage differences for organ doses for vertical shifting achieved values up to -24.5 ± 0.8% for esophagus, -20.2 ± 0.7% for lungs, -12 ± 1% for liver, -9.8 ± 0.9% for stomach, -25 ± 1% for spleen, 14.1 ± 0.7% for intestine, -10.1 ± 0.8% for pancreas, -24.2 ± 0.8% for kidneys, and 22 ± 1% for gallbladder. Concerning the arms-side configuration, the calculated percentage differences respectively showed to be up to 66 ± 2% for CTDIvol, -9.6 ± 0.4% for soft tissue GNI, 5.3 ± 0.5% for lungs GNI, -13 ± 1% for liver GNI, and 6.1313 ± 0.0007% for WED. Percentage differences for organ doses for arms-side positioning achieved values up to 38 ± 1% for esophagus, 38 ± 1% for lungs, 83 ± 2% for liver, 82 ± 2% for stomach, 76 ± 2% for spleen, 109 ± 1% for intestine, 92 ± 1% for pancreas, 98 ± 2% for kidneys, and 105 ± 2% for gallbladder. Arms positioning proved to be the major factor contributing to clinical radiation dose and image quality inconsistencies. When assessing CT procedures performance and optimization, diagnostic imaging professionals should consider that the observed variability is not only correlated with the device technology, but can also be induced by the position of the patient as well.
Nella moderna tomografia computerizzata (TC), le tecniche automatiche di modulazione della corrente (ATCM) adattano i parametri di esposizione alle dimensioni del paziente, basandosi su una o più immagini bidimensionali dello stesso acquisite (in direzione frontale e/o laterale) prima della scansione. Queste sono comunemente chiamate localizer e il loro scopo è quello di ottenere una qualità d’immagine consistente attraverso le varie dimensioni dei pazienti. Tuttavia, dati clinici di dose e qualità d’immagine mostrano variabilità anche attraverso dimensioni del paziente confrontabili, persino a parità di scanner TC. Tale variabilità potrebbe essere associata al posizionamento del paziente, visto che i localizer possono essere influenzati sia dal decentramento verticale del paziente sia dalla posizione delle estremità del paziente. Uno studio clinico per determinare le sorgenti di questa variabilità è impraticabile, in quanto comporterebbe scansioni ripetute dello stesso paziente. Di conseguenza, è stato costruito un virtual imaging trial (VIT) per valutare quanto le inconsistenze nei dati clinici siano connesse con la capacità di adattamento delle tecniche ATCM a diverse dimensioni e posizionamenti del paziente rispetto all’isocentro dello scanner. Tre pazienti virtuali (XCAT) con differenti indici di massa corporea (BMI: 24.4, 28.5, 32.2 kg/m2) sono stati sottoposti a imaging con un simulatore di uno scanner TC Siemens SOMATOM Definition Flash (DukeSim), utilizzando un protocollo clinico torace-addome. Ciascun paziente è stato acquisito in sei diverse condizioni: con le braccia posizionate sopra la testa all’isocentro (posizione standard) e a diversi spostamenti verticali (-80, -40, -20; +40 mm); e con braccia lungo il tronco all’isocentro. CTDIvol, dose all’organo (esofago, polmoni, fegato, stomaco, milza, intestino, pancreas, reni, cistifellea), global noise index (GNI) in tessuti molli e in organi specifici (polmoni e fegato), e water equivalent diameter (WED) sono stati calcolati e confrontati in termini di differenze percentuali relativamente ai valori corrispondenti alla posizione standard. Per quanto riguarda gli spostamenti verticali, la differenza percentuale per i tre pazienti ha raggiunto valori fino a 2.3 ± 0.8% per il CTDIvol, 13.1 ± 0.5% per GNI nei tessuti molli, 21.8 ± 0.5% per GNI nei polmoni, 13 ± 1% per GNI nel fegato, e -0.1566 ± 0.0006% per il WED. Le differenze percentuali per le dosi all’organo, nel caso di spostamenti verticali, hanno raggiunto valori fino a -24.5 ± 0.8% per l’esofago, -20.2 ± 0.7% per i polmoni, -12 ± 1% per il fegato, -9.8 ± 0.9% per lo stomaco, -25 ± 1% per la milza, 14.1 ± 0.7% per l’intestino, -10.1 ± 0.8% per il pancreas, -24.2 ± 0.8% per i reni, e 22 ± 1% per la cistifellea. Per quanto riguarda il posizionamento con le braccia lungo il tronco, le differenze percentuali ottenute sono risultate essere fino a 66 ± 2% per il CTDIvol, -9.6 ± 0.4% per GNI nei tessuti molli, 5.3 ± 0.5% per GNI nei polmoni, -13 ± 1% per GNI nel fegato, e 6.1313 ± 0.0007% per il WED. Le differenze percentuali per le dosi all’organo, nel caso del posizionamento delle braccia lungo il tronco, hanno raggiunto valori fino a 38 ± 1% per l’esofago, 38 ± 1% per i polmoni, 83 ± 2% per il fegato, 82 ± 2% per lo stomaco, 76 ± 2% per la milza, 109 ± 1% per l’intestino, 92 ± 1% per il pancreas, 98 ± 2% per i reni, e 105 ± 2% per la cistifellea. Il posizionamento delle braccia è risultato essere il fattore con un contributo dominante per quanto riguarda le inconsistenze nei dati clinici di dose e di qualità di immagine. In ambito di valutazione delle procedure e di ottimizzazione, occorre quindi considerare che la variabilità osservata non risulta essere unicamente correlata con la tecnologia dello scanner, ma può essere indotta anche dal posizionamento del paziente.
The Impact of Patient Positioning and Body Habitus on Clinical CT Radiation Dose and Image Quality Variability: a Virtual Imaging Trial Study
TALARICO, MARTINA
2022/2023
Abstract
In modern computed tomography (CT) scanners, automatic tube current modulation (ATCM) adapts exposure parameters to patient size based on two-dimensional (frontal and/or lateral) pre-scan images, known as localizers, in order to achieve consistent image quality across the diversity of patient body sizes. However, clinical radiation dose and image quality data exhibit variability even across comparable body habitus, and with the same CT scanner. A potential cause of this variability could be associated with patient positioning, since localizers may be affected by both patient vertical off-centering and the position of patient extremities. A clinical study to determine the sources of this variability is unfeasible because it would involve repeatedly imaging the same patient. Therefore, a virtual imaging trial (VIT) was designed to evaluate how clinical data inconsistencies are related to TCM’s capability to adapt to different patient body habitus and positioning with respect to the isocenter. Three virtual patients (XCAT) representing different body habitus (BMIs: 24.4, 28.5, 32.2 kg/m2) were imaged with a Siemens SOMATOM Definition Flash CT scanner simulator (DukeSim), using a clinical chest-abdomen protocol. Each patient was scanned under six different conditions: with arms above the head at the isocenter (standard position) and at various vertical offsets (-80, -40, -20; +40 mm); and with arms alongside the trunk at the isocenter. CTDIvol, organ dose (esophagus, lungs, liver, stomach, spleen, intestine, pancreas, kidneys, gallbladder), global noise index (GNI) in soft tissues and specific organs (lungs and liver), and water equivalent diameter (WED) were calculated and compared as percentage differences relative to the corresponding standard position values. For vertical shifts, the percentage difference for the three patients reached values up to 2.3 ± 0.8% for CTDIvol, 13.1 ± 0.5% for soft tissue GNI, 21.8 ± 0.5% for lungs GNI, 13 ± 1% for liver GNI, and -0.1566 ± 0.0006% for WED. Percentage differences for organ doses for vertical shifting achieved values up to -24.5 ± 0.8% for esophagus, -20.2 ± 0.7% for lungs, -12 ± 1% for liver, -9.8 ± 0.9% for stomach, -25 ± 1% for spleen, 14.1 ± 0.7% for intestine, -10.1 ± 0.8% for pancreas, -24.2 ± 0.8% for kidneys, and 22 ± 1% for gallbladder. Concerning the arms-side configuration, the calculated percentage differences respectively showed to be up to 66 ± 2% for CTDIvol, -9.6 ± 0.4% for soft tissue GNI, 5.3 ± 0.5% for lungs GNI, -13 ± 1% for liver GNI, and 6.1313 ± 0.0007% for WED. Percentage differences for organ doses for arms-side positioning achieved values up to 38 ± 1% for esophagus, 38 ± 1% for lungs, 83 ± 2% for liver, 82 ± 2% for stomach, 76 ± 2% for spleen, 109 ± 1% for intestine, 92 ± 1% for pancreas, 98 ± 2% for kidneys, and 105 ± 2% for gallbladder. Arms positioning proved to be the major factor contributing to clinical radiation dose and image quality inconsistencies. When assessing CT procedures performance and optimization, diagnostic imaging professionals should consider that the observed variability is not only correlated with the device technology, but can also be induced by the position of the patient as well.File | Dimensione | Formato | |
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https://hdl.handle.net/20.500.12608/81434