Discuss Imaging techniques in Orthopaedics

Imaging in Orthopaedics gives an insight about the various imaging techniques available for an Orthopaedic surgeon.

1. Discuss Imaging in Orthopaedics By Dr Joseph Famuyiwa

2. Outlines Introduction Historical Perspectives Imaging Techniques Conclusion

3. Introduction Imaging is the process of making a visual representation of something by scanning it with a detector or Electromagnetic beam Medical Imaging is the Technique and process of viewing the interior of a body for clinical analysis and medical intervention Seeks to reveal structures hidden as well as diagnose and treat diseases

4. Introduction It is a crucial aspect of day to day practice of orthopedics Different imaging modality has their limitations and complications A good knowledge of each imaging modality is essential in guiding appropriate application 4

5. Historical Perspective Joseph Nicephore Niepce (1765-1833) in 1816 invented the first camera Wilhelm Conrad Roentgen (1845-1923) discovered x-rays in 1895 Research Engineer Godfrey Hounsfield (1919-2004) in 1972 invented the first computed tomography Dr Raymond Damadian (1936-2022) in 1972 invented the first MRI machine.

6. Imaging techniques Clinical photograph Radiography(x-rays) X-rays using contrast Media Fluoroscopy Computed tomography (CT) scan Magnetic Resonant imaging (MRI) Ultrasound scan Radionuclide imaging Bone Mineral Densitometry 6

7. Clinical photograph First line imaging For Documentation and monitoring USES In trauma with soft tissue involvement In management of clubfoot pre-,intra- and post correction Angular deformities of the limb 7

8. Digital Camera Light entering through the lens strikes an image sensor The signal output by the image sensor is processed within the camera. This create image data that is stored in the memory card. Image is simultaneously view on the picture display

9. Digital Camera

10. Radiography Conventional/Plain Portable-used to evaluate acute trauma patient Digital

11. Plain Radiography Involves the use of x-rays, which are produced using an x-ray tube, whereby electrons are emitted from a heated tungsten filament and accelerated across a voltage potential to strike an opposing tungsten target. The flow of electrons from filament to the target results in a tube current, and its interaction with the tungsten target generates a spectrum of x-rays and heat Before leaving the x-ray tube, the x-rays are filtered and collimated into a useable beam After leaving the x-ray tube, the x-ray beam is directed through the patient and onto a screen/film cassette

12. Plain Radiograph ( cont ) x-ray beam is attenuated as it passes through the patient, primarily via two processes: photoelectric effect and Compton scatter before reaching the screen/film cassette, the transmitted radiation may be further collimated using a lead grid to remove the scatted radiation Screen/film cassettes are used to capture the transmitted radiation and create the latent image Intensifying screens absorb x-ray photons and subsequently emit a greater number of light photons, which are then absorbed by the film

13. Plain Radiograph( cont ) The film consists of a base, which is covered on one or both sides by an emulsion containing silver grains Absorbed light photons result in liberation of free electrons within the emulsion, which subsequently reduce the silver atoms . When the film is developed, the reduced silver atoms are amplified and appear black on the film

14. Digital Radiography What differentiates DR systems is the type of image receptor that interacts with the attenuated x-ray beam to create a medical image. screen/film cassette is replaced by a cassette containing a photostimulatable phosphor deposited onto a substrate. Lodox-LOw DOse X-ray -image achieved with 25% radiation of conventional imaging

15. Lodox machine

16. Plain radiography ( cont ) Invaluable investigation in orthopaedics -views Have wide applications such as Diagnosis Planning of surgery Intraoperative assessment of fixation of fractures Monitoring of treatment and healing Occasionally for intervention, e.g. vertebroplasty , TFSI Advantages Cheap Easily available Good in assessing bone due to its high calcium content and intrinsic contrast 17

17. Limitations exposure of the patient to ionizing radiation Ionising Radiation Medical Exposure Regulations (IRMER) 2000 Provides poor soft-tissue contrast

18. X-Rays Using Contrast Media Substances that alter x-ray attenuation characteristics can be used to produce images which contrast with those of the normal tissues C ontrast media used in orthopaedics are mostly iodine-based liquids which can be injected into sinuses, joint cavities or the spinal theca Air or gas also can be injected into joints to produce a ‘negative image’ outlining the joint cavity Ionic, water soluble iodides permit much more detailed imaging and, although also somewhat irritant and neurotoxic, are rapidly absorbed and excreted

19. X-ray with contrast( cont ) Sinography Arthrography Myelography

20. Contrast Arthrography of the knee

21. Fluoroscopy Conventional Digital Two- and Three-Dimensional

22. Conventional involves the use of low-dose x-rays to image patient anatomy Typical components of a fluoroscopy system include an x-ray tube, filters, and a collimator The x-ray tube is energized continuously using a low exposure rate, and the x-ray beam is directed through the patient onto an image intensifier. The image intensifier is responsible for converting the attenuated x-ray beam into a visible light image

23. Fluoroscopy machine

24. Conventional ( cont ) frequently coupled to a closed-circuit television camera to produce a “live” image on a video monitor An optical coupling system, using high-resolution lenses and mirrors, may also be used to direct the light image to recording devices C omponents of the image intensifier are housed in a glass vacuum tube and include a large input phosphor, a photo cathode, a series of electrostatic lenses, an anode, and a smaller output phosphor Fluoroscopy systems vary in configuration, from permanently installed biplane angiography suites to mobile C-arm designs

25. 2-D and 3-D New fluoroscopic devices obtain fluoroscopic images in an arc around the patient contain imaging processing software that provides an immediate two-dimensional (2D) or three-dimensional (3D) reconstruction of the target

26. Uses Intraoperative Imaging Surgical Navigation

27. Plain Tomography Tomography provides an image ‘focused’ on a selected plane By moving the tube and the x-ray film in opposite directions around the patient When several ‘cuts’ are studied, lesions obscured in conventional x-rays may be revealed useful for diagnosing segmental bone necrosis and depressed fractures in cancellous bone A useful procedure in former years, conventional tomography has been largely supplanted by CT and MRI

28. Computed tomography(CT) scan X-rays are delivered by a fan shaped rotating tube on a gantry Sensitive detectors record the attenuated x-rays An image is formed on a computer Each image is made up of pixels Each pixel has depth as it is 3D-termed a voxel (volume) Attenuation is the amount of x-rays absorbed by tissues Different tissues have different attenuations 29

29. CT scanning machine

30. CT scan ( cont ) Like plain tomography, CT produces sectional images through selected tissue planes – but with much greater resolution A general (or ‘localization’) view is obtained, the region of interest is selected and a series of cross-sectional images is produced and digitally recorded Slices’ through the larger joints or tissue masses may be 5–10 mm apart; those through the small joints or intervertebral discs have to be much thinner New multi-slice CT scanners provide images of high quality from which multi-planar reconstructions in all three orthogonal planes can be produced Three-dimensional surface rendered reconstructions and volume rendered reconstructions may help in demonstrating anatomical contours, but fine detail is lost in this process

31. Computerized tomography (CT) scan Hounsfield units is the attenuation co-efficient of tissues Bone is +1000 Hu Muscle is 10-40 Hu Water is 0 Hu Air is -1000 Hu There is a much wider range of attenuation co- efficients than the greyscale a human eye can perceive Therefore we use different windows for different tissue types This allows the whole range of attenuations to be displayed and improves overall detail 33

32. Computed tomography (CT) scan Uses Reconstruction possible in any plane desired Good for surgical planning in complex fractures 3D reconstruction Excellent resolution of cortical bone Better soft tissue attenuation than plain x-ray CT guided biopsy CT with contrast Limitations Availability High radiation dose More slices = more radiation Claustrophobia Patient need to lie flat for longer (never take an unstable patient to the CT scanner) Poor soft tissue contrast compared to MRI 34

33. Magnetic Resonance imaging (MRI) Uses superconducting magnets and radiofrequency coils to manipulate hydrogen ions (protons) to create a detailed, high contrast image Normally protons spin around their own random axis (nuclear spin) on application of a magnetic field (1.5-3 tesla ) Their axis of spin is aligned with the magnetic field-longitudinally In this position they are primed to absorb energy 35

34. MRI ( cont ) Present-day MRI scanners may be classified according to field strength The basic unit of measurement of magnetic field strength is the Gauss (G); the earth’s magnetic field measures approximately 0.5 G. Field strengths for MRI are much greater and are measured in Tesla (T), which is defined as 10,000 G Low-field-strength scanners are typically 0.2 to 0.3 T and are commonly used in outpatient settings as “extremity” or “open” scanners. High-field-strength scanners are generally those greater than 1 T, with 1.5-T scanners dominating the market and representing more than 90% of installed scanners worldwide

35. MRI scanner

36. MRI ( cont ) T2 signal Time taken for the protons to loose their coherence once radiofrequency turned off Water rich tissues have longer T2 time as they contain more protons Hence they release energy for a longer time and give a high signal T1 signal Time taken for 63% of the protons to return to the longitudinal spin axis Repetition time(TR) ( msec ) The time between repetition of pulses T2 images have very high TR time Otherwise the water dense tissues will not have released enough energy to be detected If the pulses are given frequently though, fat appears white rather than water Time to echo(TE) ( msec ) Time from when the pulse is stopped to when the signal is measured 38

37. MRI ( cont ) Common sequences used in orthopaedic imaging include spin-echo (SE) and gradient -echo ( gradient recalled echo [GRE]) imaging SE sequences are most frequently used in conjunction with a fast imaging technique, termed fast spinecho (FSE) or turbo spin-echo (TSE) imaging SE sequences provide T1-weighted (T1W), proton density (PD), and T2-weighted (T2W) image contrast based on selection of the parameters TR and TE

38. Magnetic Resonant imaging (MRI) Different sequences T1 weighted short TR (TR<1000ms) short TE (TE<60ms) Fat = bright Fluid = dark Defining anatomy T2 weighted long TR (TR>1000ms) long TE (TE> 60ms) Fluid = bright Defining pathology Proton density (PD) long TR(TR>1000ms) short TE(TE< 60ms) Part TI, part T2, Useful in certain situation e.g the meniscus 40

39. Magnetic Resonance imaging (MRI) Contrast = Gadolinium Rare earth metal with 7 unpaired electrons Therefore it has a high net magnetic moment It more strongly affects hydrogen ions in close proximity to the contrast This enhances the image and results in high signal on T1 scans as well Therefore shows pathologic fluid collections better (abscess) 41

40. Magnetic Resonance imaging (MRI) Advantages No ionizing radiation High quality image Can be used with contrast Abscesses and intra- articular pathology Disadvantages Claustrophobia Noisy Not tolerated well by children Availability Contraindication to MRI e.g aneurysm clips and pace makers, internal hearing aids, Metal artifact Mars sequence Over diagnosis of asymptomatic pathology 42

41. Ultrasound scan Ultrasound waves are produced by a piezoelectric ceramic crystal within a transducer By applying a voltage then reversing the voltage, contraction and expansion of the crystals surface is created This generate a compression wave-the ultrasound wave Pulse echo from tissue return to receiving transducer This again creates a voltage which is used to generate an image Depth of the structures calculated by time taken for the wave to be reflected 43

42. Ultrasound machine

43. Ultrasound scan Acoustic impedance Impedance between tissues creates echo Minimal difference between fat and muscle Most wave pass through Large difference between air and skin Most waves reflected Us gel High impedance between soft tissues and cortex High impedance = bright Low impedance = dark Different probes for different tissues High frequency probes = better resolution/superficial structures Low frequency probes = reduced resolution/ deeper structures 45

44. Ultrasound scan Advantages Non-ionizing Cheap Portable Dynamic imaging Very good for cystic structures Biopsy, injection, aspiration Disadvantages Highly operator dependent Only for superficial structures(cannot penetrate cortical bone) Limited field of view Poor resolution comparatively 46

45. Radionuclide Imaging Photon emission by radionuclides taken up in specific tissues can be recorded by a gamma camera to produce an image which reflects physiological activity in that tissue or organ The radiopharmaceutical used for radionuclide imaging has two components: a chemical compound that is chosen for its metabolic uptake in the target tissue or organ, and a radioisotope tracer that will emit photons for detection

46. Isotope Bone Scan Gamma rays emitted from a radioactive isotope of Technetium 99 bound to a phosphate to give a map of blood flow and osteoblastic activity Technetium 99 Unstable radioisotope itself Emits gamma rays Derived from the decay of molybdenum 99 It has a short half-life of 6hours It is excreted via the kidneys Protect bladder by hydration and frequent micturition 48

47. Bone Scan ( cont ) Mechanism of action Technetium-99 is attached to Hydroxymethyl diphosphonate when injected IV The HDP interact with HA crystals in bone Depending on adequate vascularity to the area in question Because HA crystals are generated by osteoblasts mineralizing bone, it is a direct reflection of osteoblastic activity The gamma rays emitted by the T-99 are detected by a gamma camera A digital image is created giving a map of blood flow and osteoblastic activity 49

48. Bone scan ( cont ) • The 3 phases of a triple bone scan are: Vascular phase (2-5sec.) Shows arterial flow and hyper-perfusion Blood pool phase (after 5min) Shows bone and soft tissue hyperemia Infection / inflammation Static phase (3hrs) Soft tissue activity has cleared leaving only bone activity 50

49. Radionuclide imaging ( cont ) Single-photon emission computed tomography-CT (SPECT-CT) Gamma camera with CT component on the same scanner Multi-planar imaging Increasing resolution, decrease noise and increase localization Positron emission tomography-CT (PET-CT) Exploiting increase metabolic rate of tumors i.e glucose consumption e.g deoxyglucose labelled 18Flourine (1/2 life 112 min.) 51

50. Radionuclide imaging (bone scanning) WBC scan Labeling patient’s own WBC with radioactive tracer such as indium Accumulates in the reticuloendothelial system e.g bone marrow, liver and spleen but also areas of active infection Hybrid PET-MRI Potential increase bone metastasis assessment and response to treatment 52

51. Radionuclide imaging (bone scanning) Advantages : Tumors (metastatic and primary esp in spine) Infection – osteomyelitis Stress fractures Prosthetic loosening/pain Paget's Disadvantages Poor specificity although very sensitive Radiation dose is fairly high False negative in areas of low blood supply E.g avascular bone, lytic tumor False negative in myeloma Myeloma inhibits osteoblasts 53

52. Bone Mineral Densitometry Bone mineral density (BMD) measurement is now widely used in identifying patients with osteoporosis and an increased risk of osteoporotic fractures Techniques - Radiographic Absorptiometry (RA) -Quantitative Ultrasonometry (QUS) -Quantitative Computed Tomography (QCT) -Dual Energy x-ray Absorptiometry (DEXA)

53. DEXA scans • DEXA scanning Dual energy x-ray absorptiometry Utilizes x-rays of different energies Absorbed in different proportions by bone and soft tissue Used to assess bone mineral density Scans of femur and lumbar spine centered on L3 are taken 55

54. DEXA scans Result interpretation Units of bone mineral density are g/cm² Values are related to the peak BMD of a young adult or matched by age The T score represents comparison with peak BMD of a young adult The Z score represents the age-matched score Sex and race are match in both Only difference is age matching in the z score The T score is used to determine whether there is osteoporosis The Z score is used to assess whether the reduced BMD is related to another cause i.e lower than expected for age 56

55. DEXA scans WHO criteria for osteoporosis relies on the T score +1 to – 1 = normal <-1 to -2.5 = osteopenia < -2.5 to -4.0 = osteoporosis Disadvantages No differentiation between cortical and cancellous density Falsely high BMD in fractured sclerotic vertebrae and degenerative disease 57

56. DEXA scans 58

57. General application in orthopaedics Imaging is applied in orthopaedics practice in Diagnosis, classification and staging of diseases Preoperative planning and templating Intraoperative monitoring Therapeutic purposes Monitoring of treatment and healing process 59

58. DIAGNOSIS Almost all of the modalities are used to make or confirm diagnosis Plain radiography plays an invaluable role especially in trauma CT scan usually augments plain radiograph, though plays important role in complex trauma Biopsies can be US, fluoroscopic or CT-guided DDH, joint collection by USS Bone scans Bone densitometry 60

59. PREOPERATIVE PLANNING Plain radiographs, CT scan with 3D reconstruction and MRI Plain radiographs used in templating MRI especially in spine, ligamentous injuries, oncology 61

60. INTRAOPERATIVE Fluoroscopy in fracture fixations Limb reconstructions Corrective osteotomies Spine fixations Minimally invasive surgeries and closed reductions and fixation 62

61. THERAPEUTIC/INTERVENTIONAL PROCEDURES Arthrography /Diagnostic-therapeutic injections Facet injections Discography Vertebroplasty 63

62. MONITORING Fracture healing and status of the implants Endoprostheses Effect of treatment, e.g. Ricketts, osteoporosis 64

63. Risks Cell death and distorted replication Cancers Thyroid 85% of papillary cancers thought to be radiation related others skin, breast, etc Cataracts Reducing risk (measures) Justify, optimize , limit PPE Scatter The annual whole body Dose Equivalent Limit for occupationally exposed persons is 20mSv-ICRP 65

64. Conclusion Imaging is paramount in orthopaedics practice Sound knowledge and broad understanding of radiological techniques they applied to orthopaedics is important for the orthopaedic surgeons 66

65. Thank you for listening 67

66. References Rockwood C.A. et al. Rockwood and Green’s Fractures in Adults 6 th ed. Lippincott-Raven. Philadelphia. 2004. Loius Solomon et al. Apley’s System of Orthopaedics and Fractures 9 th ed .Hodder Arnold ;an Hachette UK company 2010. Michael W. Chapman et al. Chapman Orthopedic Surgery 3 rd ed. Jan 2001 https://en.Wikipedia.org Power points by Drs Ugwu and Orekha 68