Computed Tomography: Optimization of acquisition protocols & Justification of clinical referrals. Koos Geleijns, medical physicist

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1 Computed Tomography: Optimization of acquisition protocols & Justification of clinical referrals Koos Geleijns, medical physicist

2 CT delivers excellent 3D image quality

3 CT delivers excellent 3D image quality

4 CT delivers excellent 3D image quality

5 CT delivers excellent 4D image quality

6 CT delivers excellent image quality, but...

7 Optimization of acquisition protocols Tube current optimization Tube current modulation Selective organ shielding Unexpected circumstances

8 Optimization Aspects of optimization not discussed here: Tube voltage (lower tube voltage in iodine contrast enhanced scans) Rotation time Pitch Reconstruction filter Slice thickness Overbeaming (penumbra effect): beam as wide as possible Overranging (extra rotatoins before and after the planned range): beam as small as possible Image reading, special postprocessing, image reformats, quality of the workstation

9 Tube current optimization (fixed ma) Children undergoing CT scans are routinely getting adultsize doses of x-rays (2000)

10 Tube current optimization (fixed ma) Depending on the age/size Adults vs children; compensation for the x-ray attenuation Normal, obese vs small sized adults; compensation for the composition (soft tissue vs fat tissue) Depending on the clinical question For example CT brain: orbita very low dose, ventricles low dose, brain (white and grey) higher dose. How? In cooperation with manufacturer and radiologists (consensus); scientific research; trial and error; legislation (European Guidelines).

11 Low dose acquisitions in coronary CT angiography Joemai, Geleijns, Veldkamp, European Radiology

12 Low dose acquisitions in coronary CT angiography 100 % 50 % 25 % 12.5 % Joemai, Geleijns, Veldkamp, European Radiology

13 Low dose acquisitions in CT brain 100% 50% 25% 12.5%

cm Single beat, 128 mm range, 100 kv, 320 ma,

14 Low dose acquisitions in coronary CT angiography Clinical image quality, LUMC sub msv volumetric heart scan (dr. Kroft) Cx > 50 % stenosis 72 yom, 82 kg, 178 cm Single beat, 128 mm range, 100 kv, 320 ma, BMI 26 (overweight), 55 bpm 80 ml contrast, 0.35 s rot. time, 256 x 0.5 mm

15 Diagnostic reference level (European Guidelines) The diagnostic reference level is in The Netherlands supplemented by an achievable (optimized) dose level This is done to stimulate optimization of scan protocols Diagnostic reference levels and achievable dose levels for computed tomography, volume computed tomography dose index and dose -length product (average adult). Diagnostic reference level Achievable dose level CT abdomen/pelvis, acute abdomen CTDIvol100: 15 mgy DLP: 700 mgy cm CTDIvol100: 8 mgy DLP: 400 mgy cm CT chest angiography, lung embolism CTDIvol100: 10 mgy DLP: 350 mgy cm CTDIvol100: 6 mgy DLP: 200 mgy cm Pediatric CT head; trauma (age 0 (neonate), 1, 5, 10 year)

16 Helical scan, tube current modulation To assist the optimization of CT acquisitions, scanner manufacturers have developed tube current modulation (TCM) techniques Currently, these can be divided into three main categories: angular modulation in the xy-plane, longitudinal modulation along the z-axis; and volumetric (combined) modulation in the xyz-volume TCM should provide more uniform image quality with reduced interpatient and intrapatient variability. In addition, it has potential for dose reduction

17 Helical scan, tube current modulation Longitudinal modulation (along the z-axis)

Tube current modulation works good! Noise (HU) TCM Noise versus SD Level 40 38 36 34 32 30 28 26 24 22 20 18 16 P75 Max Median Min P25 130mA DLP 450.2 L 32SD L 30SD DLP 332.2 DLP 372.

18 Tube current modulation works good! Noise (HU) TCM Noise versus SD Level P75 Max Median Min P25 130mA DLP L 32SD L 30SD DLP DLP L 28SD L 26SD DLP DLP L 24SD C 32SD* C 30SD* C 28SD C 26SD C 24SD DLP DLP DLP DLP DLP DLP SD level Box-and-whisker plots of the noise variations along the z-axis in the Rando Alderson phantom abdomen for scans using fixed tube current and with longitudinal and combined tube current modulation with variable SD.

19 Review of 43 papers, 64 row Coronary CT Angiography 15 msv 12 msv 13.5 msv 4 msv < 1 msv??

20 In-plane bismuth shielding: eye lens, thyroid Eye shield in place. Hopper et al. AJNR 2001Clin Thyroid shield in position. McLaughlin et al. Clin. Radiol. 2004

21 In-plane bismuth shielding: breasts (pediatric CT)

22 In-plane bismuth shielding: dose and image quality Absorbed dose to superficial organs and tissues was reported to be reduced by applying bismuth shielding on the skin close to superficial organs and tissues. Deterioration of image quality by beam hardening artefacts but they did not to extend to the tissues of interest for diagnosis, No obvious change in image quality resulted from shielding The artefact produced by shielding was reported as slightly distracting but did not interfere with interpretation of the images.

23 In-plane bismuth shielding: frontal view

24 In-plane bismuth shielding: frontal and lateral view

compromise image quality, increase noise level and introduce streak artifacts.

25 Quantitative assessment of dose and image quality (2008) Sabrina Vollmar and Willi Kalender, Eur Radiol (2008) 18: Bismuth shielding may compromise image quality, increase noise level and introduce streak artifacts. We do not recommend the use of bismuth shielding because of their impact on image noise.

be achieved more efficiently by a reduction of tube current.

26 Quantitative assessment of dose and image quality (2006) The observed reduction of organ dose and total energy imparted could be achieved more efficiently by a reduction of tube current. The application of in-plane selective shielding is therefore discouraged.

27 Optimization Be alert for unexpected circumstances.

Badly performed AND repeated brain CT perfusion studies cause hair loss in three patients (MDCT) 2003 Radiation-induced temporary hair loss after cerebral perfusion studies with multi-detector CT,

28 Badly performed AND repeated brain CT perfusion studies cause hair loss in three patients (MDCT) 2003 Radiation-induced temporary hair loss after cerebral perfusion studies with multi-detector CT, Imanishi et al., ECR patients, each one or more MDCT perfusion studies, some also DSA The combination of two or more MDCT perfusion studies, at a rather high tube current, and angiography resulted in hair loss in three patients

29 Badly performed brain CT perfusion studies in many patients 2009

a lawsuit filed by the parents Knickerbocker tried to start

30 Badly performed AND repeated CT brain study The toddler received 151 scans in a single imaging session Civil trial in a lawsuit filed by the parents Knickerbocker tried to start the examination, but the machine did one rotation before it stopped.

31 Image artifacts in a brain scan

32 Justification of clinical referrals Currently: mainly based on consensus Our aim: evidence-based CT referral

33 Need for justification of clinical referrals! In 2006, Americans were exposed to more than seven times as much ionizing radiation from medical procedures as was the case in the early 1980s. ± 3 msv/y

34 Need for justification of clinical referrals!

35 Need for justification of clinical referrals! Target: referring physicians and radiologists Currently practice in justification and referral: Individual decisions (referring physician) Local practices National guidelines European referral guidelines (and quality criteria) American appropriateness criteria Drawbacks in current referral practices: Mainly based on consensus, few evidence based practices No scientific consideration of all relevant aspects

36 Our aim: evidence-based CT referral A patient presents with signs and symptoms a sign is an objective symptom of a disease; a symptom is a subjective sign of disease Medical history & physical examination, (anamnesis) Clinical decision 1 Clinical examination Lab test, organ function Clinical decision 2 Wait and see no treatment Clinical decisions may be supported by objective clinical decision rules Medical imaging Clinical decision 3 Treatment

37 Our aim: evidence-based CT referral X-ray (plain radiograph, mammography) Computed tomography (CT) Ultrasound (US) and Doppler ultrasound Magnetic resonance (MR) imaging Nuclear medicine (SPECT, PET)

38 Radiation protection: conscious utilization of CT CT is accurate, rapid, reproducible, and convenient But. CT is associated with radiation exposure Our aim: evidence-based CT referral, by: Assessment of outcomes: disability weights (WHO) Evidence-based: systematic review, patient studies Model-based stepwise guideline development All relevant aspects can now be taken into account: Medical History and Physical Examination ; Lab Tests ; Possible Imaging Modalities ; consequences of false negatives and false positives (morbidity and mortality); adverse effects, including radiation induced effects (morbidity and mortality)

Bayesian network for probability of CAD based on the most important test results prior to imaging or intervention Decision analysis is based on the premise that humans are reasonably capable of

39 Bayesian network for probability of CAD based on the most important test results prior to imaging or intervention Decision analysis is based on the premise that humans are reasonably capable of framing a decision problem, listing possible decision options, determining relevant factors, and quantifying uncertainty and preferences, but are rather weak in combining this information into a rational decision. A Bayesian network, or belief network, shows conditional probability and causality relationships between variables.

40 Radiation protection: conscious utilization of CT Acute abdominal pain

41 Radiation protection: conscious utilization of CT Symptom: Appendicitis First: Suspected appendicitis scoring Next: Assess the optimal imaging policy

42 Radiology: ultrasound and CT of the abdomen CT (upper) and US (lower) of acute appendicitis in a 25-year-old man [Keyzer-ea Rad 2005]

43 Radiation protection: conscious utilization of CT treatment, follow-up, additional diagnosis

44 Radiation protection: conscious utilization of CT The biggest challenge in radiation protection (in diagnostic radiology) nowadays is to extend the scientific basis for conscious utilization of x-ray imaging, particularly for CT Cost effectiveness may be considered Proper justification is relevant for diagnosis and follow up Should CT be performed or not; when should CT be performed? Benefits of diagnosis and treatment Risks of diagnosis and treatment (including radiation exposure)

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