Authors: Cabral, Ricardo 1 ; Carvoeiras, Pedro 2 ; Fatana, João 2, ; Alves, Rita 1. 1 Centro Hospitalar Lisboa Norte - Hospital de Santa Maria; 2

Transcription

1 Authors: Cabral, Ricardo 1 ; Carvoeiras, Pedro 2 ; Fatana, João 2, ; Alves, Rita 1. 1 Centro Hospitalar Lisboa Norte - Hospital de Santa Maria; 2 Medical Consult, SA;

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3 Establish a method to correlate image noise with individual demographic characteristics of each patient ; Optimize acquisition parameters without losing diagnostic quality.

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5 Data standardization in CT guaranties a correct image exposure a fixed amount of radiation attenuation; CT users don t always know when/how to lower mas/kvp.

6 Quality of the exam changes, differing the level of image noise, with patients of different body types; There has been a tendency to increase mas (dose) in order to lower image noise.

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8 Technical / Demographical Parameters Age; Antero- posterior (AP) and lateral (LAT) diameter; Weight; KVp; mas; Pitch; Slice thickness; Kernel; Height; CTDIvol; DLP; Scan Length; SD; Exam Head Lumbar Spine Chest Abdomen Pelvis Abdomen +Pelvis Sample Weight Slice CTDIvol Noise kvp mas (Kg) (mm) (mgy) (HU) male 38 min female 61 median total 99 max male 27 min female 47 median total 74 max male 15 min female 11 median total 26 max male 9 min female 9 median total 18 max male 10 min female 5 median total 15 max male 9 min female 12 median total 21 max Philips equipments 16 and 64 slice Brilliance / 4 slice Mx8000.

9 Tomografia Computorizada TC 1 (16cortes) Pa#ent ID Região anatómica Sexo Idade Altura (m) Peso (kg) ) (mgy) DLP (mgy*cm) Modulação de Dose kv mas Espessura de corte (mm) Pitch da aquisição (cm) Kernel Espessura (cm) Largura (cm) ROI (SD)

10 The standard deviation, was used as a quantity marker. q One image is chosen, and a ROI is drawn with 2 to 5 cm 2, in a homogeneous region ;

11 The images were digitally manipulated adding different levels of noise, simulating an mas lowering: Adaptation of the used mas (pseudo mas) to reduce the dose: Head Lumbar Spine Chest Abdomen Pelvis

12 Image quality was determined by two Radiologists; q The noise was evaluated without knowledge of the dose and technical parameters. Criteria to evaluate Image Quality Anatomic Criteria Physic Criteria Diagnostic Value General Quality Evaluating system Image Quality Score Unacceptable 1 Sub - Acceptable 2 Acceptable 3 Good Quality 4 High Quality 5

13 Image test with diferent noise levels added, using the Image J software: 350mAs 315 mas (- 10%) 262 (- 25%) mas 210 mas (- 40%) SD +4% SD +10% SD +27% SD

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15 Percentile 75 of local DRL's: Local DRL s European DRL s Exam CTDIvol CTDIw DLP CTDIw DLP Head Lumbar Spine Chest Abdomen Pelvis Abdomen+Pelvis

16 Quantitative evaluation: relation between image noise with radiation dose and demographic factors (Abdomen) y = x R² = Noise Noise y = x R² = Effective Diameter (cm) Noise y = x R² = IMC Weight (Kg)

17 Noise Quantitative evaluation: relation between image noise with radiation dose and demographic factors (Chest) y = x Noise R² = y = 0.446x R² = Effective Diameter (cm) IMC Ruído y = x R² = Peso (Kg)

18 Quantitative evaluation: relation between image noise with radiation dose and demographic factors (Lumbar Spine) y = x R² = Noise y = x R² = Effective Diameter (cm) y = x R² = Noise Noise IMC Weight (kg)

19 Quantitative evaluation: relation between image noise with radiation dose and demographic factors (Head) 9 y = x R² = Noise Effective Diameter (cm)

20 Relation of image noise with mas from PMMA phantoms SD (HU) mas product (mas) Chest Head Abdomen Lumbar Spine Linear (Chest) Linear (Head)

21 Quality perception in test images with added noise Image Quality (Noise) Score Abdomen CT images Score Pseudo mas Image Quality (Noise) Score Lumbar Spine CT images Score Pseudo mas Image Quality (Noise) Score Chest CT images Score Pseudo mas Def [20-24] cm Def [30-34] cm Def [25-29] cm Def >35 cm Def [20-25] cm Def [31-36] cm Def [26-30] cm Def >37 cm BMI [15-20[ Kg/m^2 BMI [25-30[ Kg/m^2 BMI [20-25[ Kg/m^2 BMI >=30 Kg/m^2

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23 Test images evaluation with the added noise and mas reduction as proposed Lumbar Spine: Def(cm) Routine mas Target Score Noise Increased Modified mas Dose Reduction % % % % % % > % 435 0% Abdomen : Def(cm) Routine mas Target Score Noise Increased Modified mas Dose Reduction % % % % % % > % % Chest: BMI(kg/m^2) Routine mas Target Score Noise Increased Modified mas Dose Reduction % 75 25% % % % % > % 160 0%

24 Dose reduction by exam type mas reduction in standard Abdomen protocol mas reduction in standard Chest protocol 40% 30% 20% 10% 0% [20-25[ [25-30[ [30-35[ 35 25% 20% 15% 10% 5% 0% [20-25[ [25-30[ [30-35[ 35 mas reduction in standard Lumbar Spine protocol 30% 20% 10% 0% [15-19[ [20-24[ [25-29[ >30

25 Results show that the dose can be individually adapted while acquiring a CT exam with good quality wanted noise levels; Dose adjustment depend on size/weight and age of each patient; The image analysis helped the radiologist to determine the dose adjustment that would produce good images.

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27 The dose must be individually adapted, with the need to standardize protocols and technical parameters adapted to the patient demographic characteristics (BMI and Effective Diameter); Radiologists have different acceptability of noise each department needs to adapt their noise levels, never exceeding the DRL s.

28 THANK YOU

29 REFERENCES

30 CT Image Quality, Wil Reddinger, M.Sc., R.T.(R)(CT); OutSource, Inc; Apr ICRP, International Commission on Radiological Protection. Recommendations of the International Commission on Radiological Protection. ICRP Publication 60; ICRP, International Commission on Radiological Protection. Managing Patient Dose in Multi- Detector Computed Tomography (MDCT). ICRP Publication 102. Annals of the ICRP 37,;Elsevier, IAEA,dose reduction in CT while Maintaining Diagnostic Confidence: A Feasibility/Demonstration Study, Vienna Sep European guidelines on quality criteria for computed tomography. Luxembourg: office for official Publications of the European Communities; X Ray CT, Nick Keat, ImPACT ST. George's Hospital; accessed

31 ACKNOWLEDGMENT

32 Serviço de Imagiologia Hospital de Santa Maria; Medical Consult.