A rabbit phantom study to reduce neonatal radiation dose without compromising image quality.

[摘要] English: Neonates who are ill at birth often require a large number of radiographs during the period ofhospitalization. Radiography refers to the imaging of body parts using x-rays and plays animportant role in the diagnosis and follow-up of patients suffering from various medicalconditions.X-rays fall into the category of ionizing radiation which has the potential to cause cell damageand therefore are associated with a radiation risk. The radiation risk to these neonates is higherthan in adults. Therefore the dose should be kept as low as reasonable achievable (ALARA)while still rendering images that comply with the diagnostic task.Large variations have been found with respect to the beam parameters used to acquireneonatal anterior posterior (AP) chest x-ray images, emphasizing the need for optimization.Changing the beam parameters will not only influence the radiation dose, but also the imagequality. Although physical image quality metrics such as contrast, resolution and noise can beused to quantify image quality these metrics do not give an indication of the diagnostic imagerequirements. Subjective image evaluation using appropriate phantoms is therefore alsorequired. AimThe aim of this phantom study was to reduce neonatal radiation dose while maintainingdiagnostically adequate image quality for neonatal radiography.MethodsEntrance surface doses (ESD) and exit doses were determined for the beam parameters (55 kV,2 mAs no additional filtration) used to acquire neonatal AP chest x-rays at Universitas AcademicHospital (UAH). Beam parameter combinations, reducing the ESD by 50 % or more compared to the current practice, were then selected keeping the dose to the Computed Radiographyimaging plate (detector) constant. The effect of using different beam parameters on the imagequality was investigated, using a chicken corpse as a phantom to simulate the neonatal chest.The contrast as well as contrast to noise ratios were determined. Ten observers comprisingradiographers, radiologists and a medical physicist were then tasked to evaluate the overallsubjective image quality using a multiple rank order method.Based on the image quality ranking the beam parameters delivering acceptable image qualitywere then used to image five living (sedated) rabbits with a weight of approximately 2000g,simulating the neonatal chest with a heart and lungs. Eight radiology registrars gave theiropinion on the diagnostic quality of the images using a five-point scale. These radiologists thenevaluated the image quality subjectively using the multiple rank order method with the focuson three anatomical regions namely the lung patterns, the heart borders and the diaphragm.Results and DiscussionThe contrast and contrast to noise ratio stayed constant in the range 55 �?66 kV, indicating theinfluence of post processing on digital images. Large variation in observer opinion of imagequality was seen for both the chicken and rabbit phantom images obtained with different beamparameters (different dose values). Even amongst a single observer large variation in theiropinion was seen when evaluating images of different rabbits at the same beam parameters.All the images were regarded as being diagnostically acceptable. This indicates that a lowerdose option could be selected without compromising the diagnostic value of the images.ConclusionThe chicken phantom proved to be a good simulation of the neonatal chest; however when oneneeds to investigate clinical features the rabbit phantom would be recommended. This studyshows a possible dose reduction of 64 % when using beam parameters 60 kV, 2.0 mAs and2 mm Al additional filtration.Afrikaans: InleidingSiek neonate benodig 'n groot aantal x-straal beelde tydens hospitalisasie. X-straal beelde val indie kategorie van ioniserende straling en hou dus 'n stralingsrisiko in. Hierdie stralingsrisiko ishoër in neonate as in volwassenes. Dit is om hierdie rede belangrik om te verseker dat dielaagste moontlike stralings dosis gebruik word.Die variasie in bundel parameters (kV, mAs en filtrasie) wat gebruik word vir neonatale anteriorposterior borskas x-straal beelding dui op die noodsaaklikheid van optimalisering. 'nVerandering in die bundel parameters beinvloed nie die stralings dosis alleenlik nie, maar ookdie beeld kwaliteit.Alhoewel beeldkwalitiet parameters soos kontras, resolusie en geruis gebruik word om diebeeld kwaliteit te kwantifiseer gee die parameters egter nie 'n aanduiding of die beeld aan diediagnostiese vereistes voldoen nie. Vir hierdie doel is subjektiewe evaluasie van beeldkwaliteitmet gebruik van die geskikte fantome genoodsaak.DoelDie doel van die fantoom studie was om die neonatale stralings dosis te verminder sonder omdie diagnostiese beeldkwaliteit te verlaag.MetodesDie ingangsdosis en uitgangsdosis was bepaal vir die bundel parameters (55 kV, 2 mAs en geenaddisionele filtrasie) huidiglik in gebruik by die Universitas Akademiese Hospitaal (UAH).Bundel parameter kombinasies wat die ingangs dosis met 50 % of meer verminder het, terwyldie detektor dosis konstant gehou is, is gebruik. 'n Hoender fantoom is gebruik om die neonatale borskas te simuleer in 'n poging om die effek van die gekose bundel parameters opdie beeldkwalitiet te ondersoek.Die kontras en kontras-tot-geruis vehoudings is bepaal. Tien waarnemers wat radiograwe,radioloë en 'n mediese fisikus insluit, het die beelde geëvalueer op grond van algemenebeeldkwaliteit mbv. 'n veelvuldige rangorde metode.Die bundel parameters wat aanvaarbare beeldkwaliteit gelewer het, is gebruik om x-straalbeelde van vyf lewendige (gesedeerde) konyne, met 'n massa van ongeveer 2000g, te verkry.Die konyne is gebruik om die neonatale borskas met 'n hart en longe te simuleer.Agt radiologie kliniese assistente het die konyn beelde geëvalueer m.b.v. 'n vyf-punt skaal. Diebeeldkwaliteit is ook subjektief geëvalueer mbv. die veelvuldige rangorde metode met die fokusop drie anatomiese dele naamlik die long patrone, hart rande en diafragmas.Resultate en BesprekingDie kontras en kontras-tot-geruis verhoudings het konstant gebly in die reeks 55 �?66 kV. Ditgee 'n aanduiding van die invloed wat 'post verwerking op die digitale beeld het. Grootvariasies in waarnemer opinie van beeldkwaliteit is waargeneem, in beide die hoender enkonyn fantoom beelde, met die gebruik van verskillende beeld parameters. Die verskille wasselfs waargeneem vir 'n enkele waarnemer tydens die evaluasie van die vyf konyn beelde by 'nbundel parameter kombinasie.Al die beelde was van aanvaarbare diagnostiese kwaliteit wat aandui dat 'n bundel parameterkombinasie met 'n laer stralings dosis gebruik kan word.GevolgtrekkingDie hoender fantoom het die neonatale borskas goed verteenwoordig. Die konyn fantoomword egter aanbeveel wanneer gedetaileerde kliniese strukture evalueer moet word. Die studiebewys dat 'n dosis vermindering van 64 % moontlik is met die gebruik van bundel parameters60 kV, 2.0 mAs en 2 mm Al addissionele filtrasie.

[发布机构] University of the Free State