Different types of imaging techniques in orthopaedics. Usg Xray Ct scan Mri

1. IMAGING TECHNIQUES
Presented by
Dr Binod Chaudhary
Department of Orthopaedics
WRH, PoAHS

2. Contents
• Introduction
• Historical perspective
• Classification of different types of imaging techniques
• General application of imaging in orthopaedics
• Conclusion

3. INTRODUCTION
• A veritable tool in the evaluation of surgical patients.
• Many surgical diagnoses can be made with clinical assessment.
However, radiological investigations remains vital to the diagnosis,
preparation and follow up of patients
• A myriad of imaging options are available.
• Initial application of radiography lay in the demonstration of fractures
and radio-opaque foreign bodies.
• Subsequent parallel development of Radiology and Orthopaedics had
broaden the scope.
• Today, high precision interventional therapeutic procedure can be
carried out.

4. HISTORICAL PERSPECTIVE
• Wilhelm Conrad Rontgen: discovered x-rays(1895). Nobel prize in
1901 (father of radiology).
• 1920: use of contrast for x ray studies
• 1950s: nuclear medicine was born
• 1970s: ultrasound came into use
• Sir Godfrey Hounsfield invented CT in 1975.

5. USES OF RADIOLOGICAL TECHNIQUES
• To aid diagnosis of a medical and/or surgical disorder
• To guide a surgical procedure
• Monitoring
• Interventional radiological techniques

6. CLASSIFICATION OF IMAGING TECHNIQUES
Current techniques in practice of orthopaedics include:
• Clinical photograph
• X-rays (plain radiographs)
• Fluoroscopy
• Ultrasound
• Computed tomography
• Magnetic resonant imaging
• Radionuclide scanning
• Bone densitometry

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,
etc

8. X-RAYS (PLAIN RADIOGRAPHY)
Electromagnetic radiation
• Travel at speed of light ~3,00,000 km/s
• Not affected by electric or magnetic fields
• Travel through vaccum

9. X-RAYS (PLAIN RADIOGRAPHY)
Definition
• High energy radiation which undergo differential absorption by
tissues as they pass through the body
• Generated via interactions of the accelerated electrons with electrons
of tungsten nuclei within the tube anode.
• 2 types of x-rays generated: Characteristic radiation and
Bremsstrahlung radiation.

10. Characteristic Radiation Bremsstrahlung radiation

11. • Quantity of x-rays generated: directly proportional to number of
moving electrons.
• Quality of x-rays generated: proportional to the speed of the
electrons
• 2 outcomes when x-rays interacts with matter
1. Photoelectric absorption
2. Compton scattering

12. Basics of X-ray physics
• Travel in straight lines
• Body parts further away
from the detector are
magnified compared with
those that are closer and
vice versa.
• A source tat is too near the
patient will further
exaggerate the size of
structures nearest to that
sources.

13. Tissue densities
• an x-ray image is a map of x-
ray attenuation
• Attenuation of x-rays is
variable depending on
density and thickness of
tissues
• Describing x-ray
abnormalities in terms of
density may help in
determining the tissue
involved.
• The greatest contrast is
found in areas of greatest
difference in density of
adjacent structures.

14. Uses
• Invaluable investigation in orthopaedics
• Have wide application such as
Diagnosis
Planning of surgery
Intraoperative assessment of fixation of fractures
Monitoring of treatment and healing
Occasionally for interventions eg. Vertebroplasty, SNRB.
Advantages
• Cheap
• Easily available
• Good in assessing bone due to its high calcium content and intrinsic
contrast.

15. COMPUTED TOMOGRAPHY(CT) SCAN
• One of the major advances in radiology
in recent years.
• Uses a computer to create an image
from an integration of multiple xrays
exposures taken in a circle round the
patients.
• Heavy ionizing radiation dose.

16. • Attenuation: amount of x-rays absorbed by tissues
(different for different tissues)
• Hounsfield units describe the attenuation co-
efficient of tissues
• Bone=1000 Hu
• Water= 0 Hu
• Air= -1000 Hu
• There is a much wider range of attenuation co-
efficient than the greyscale a human eye can
perceive
• Different windows for different tissue types
allowing the whole range of attenuation to be
displayed and improves overall detail.

17. Advantages
• Reconstruction possible in any plane desired
• Good for surgical planning in complex fractures-
3D reconstruction
• Exellent resolution of cortical bone
• Better soft tissue attenuation than plain x-ray
• CT guided biopsy
• CT with contrast
Disadvantages
• Availability
• High resolution dose
• Claustrophobia

18. MRI
• Newest of the imaging techniques
• Does not use ionizing radiation
• Principle: body tissues consists of
protons/electrons. In a strong uniform
field such as MRI scanner, these nuclei
align themselves with the main magnetic
field.
A brief radiofrequency, pulse is applied
to alter the motion of the nuclei. When
removed, the nuclei realign with the
main magnetic field, emitting energy(RF
signal).

19. • 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

20. • Repitition 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 detect pulses are given frequency 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.

21. • Differential sequences
• T1 weighted- short TR (TR<1000 ms), short TE(<60 ms)
fat=bright
fluid= dark
defining anatomy
• T2 weighted- long TR (TR>1000ms), long TE (TE>60 sec)
Fluid= bright
Defining pathology
• Proton density (PD)- long TR(TR>1000ms), short TE(TE<60ms)
• Part T1, Part T2
• Useful in certain situations e.g. the meniscus

22. • Contrast (Gadolinium)
• High net magnetic moment
• More strongly affects hydrogen
ions in close proximity to the
contrast.
• Enhances the image and results in
high signal on T1 scans as well.
• Shows pathologic fluid collections
better.

23. • 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 artifacts: MARS sequence
• Over diagnosis of asymptomatic

24. ULTRASOUND
• Second most common method of
imaging
• Relies on high frequency sound waves
generated by a transducer containing
piezoelectric material
• Principle:
generated sound waves are
reflected by tissue interfaces and, by
ascertaining the direction and the time
taken for a pulse to return, it is possible
to form an image.

25. Acoustic impedance
• Impedance between tissues creates echo
• Minimal differences between fat and
muscle(most waves pass through)
• Large difference between air and
skin(most waves reflected-use gel)
• High impedance=bright
• Low impedance= dark

26. 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 fiew
• Poor resolution comparatively

27. BONE SCAN(RADIONUCLIDE IMAGING)
• 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
• Emits gamma rays
• Derived from the decay of molybdenum 99
• Short half life of 6 hours
• Excreted via kidney (bladder hydration and

28. Mechanism of action
• Technetium-99 is attached to methyl
diphosphonate(MDP) when injected iv
• The MDP 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 dected
by a gamma camera
• A digital image is created giving a map of blood
flow and osteoblastic activity

29. Radionuclide imaging….
3 phases of triple bone scan
• Vascular phase (1-2min)
• Blood pool phase (3-5 min)
• Static phase(4 hrs)

30. Radionuclide imaging…
• 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 rato of tumors i.e glucose
consumption
• E.g deoxyglucose labelled 18 Fluorine (1/2 life-112 min)

31. Radionuclide imaging…
• WBC scan
• Labelling patient’s own WBC with radioactive tracer such as
indium
• Accumulation 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

32. Useful for
• Tumors (metastatic and primary esp in spine)
• Infection-osteomyelitis
• Stress fractures
• Prosthetic loosening/pain
• Paget’s disease
Disadvantages
• Poor specificity although very sensitive
• Radiation dose is fairly high
• False negative in areas of low blood supply-e.g avascular bone, lytic
tumors

33. DEXA scan
• Dual energy x-ray absorbimetry
• Utilizes xrays of different energies
• Absorbed in different proportions by
bone and soft tissues
• Used to assess bone mineral density

34. Result interpretation
• Units of bone mineral density are g/cm3
• Values are related to the peak bone mass density 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 matched 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

35. WHO criteria for osteoporosis relies
on T score
• 0 to -1 =normal
• -1 to -2.5= osteopenia
• <-2.5 = osteoporosis
• <-2.5 +fragility fracture=severe
osteoporosis
Disadvantages
• No differentiation between cortical
and cancellous density
• Falsely high BMD in fractured
sclerotic vertebrae and degenerate

36. GENERAL APPLICATION OF IMAGING IN
ORTHOPAEDICS
General applications
• Diagnosis, classification and staging of diseases
• Preoperative planning and templating
• Intraoperative monitoring
• Therapeutic purposes
• Monitoring of treatment and healing process

37. Diagnosis
• Almost all the modalities are used to make or confirm diagnosis
• Plain radiography plays an invaluable role especially in trauma
• CT scan usuallu augments plain radiograph, though plays important
role in complex trauma
• Biopsies can be US, fluoroscopic or CT-guided
• DDH, Joint collection by US scanning
• Bone scans
• Bone densitometry

38. Pre operative planning
• Plain radiographs, CT scans with 3D reconstruction and MRI
• Plain radiographs used in templating
• MRI especially in spine, ligamentous injuries, oncology

39. Intraoperative
• Fluoroscopy in fracture fixations
• Limb reconstructions
• Corrective osteotomies
• Spine fixations
• Minimally invasive surgeries and closed reductions and fixation

40. Therapeutic/interventional procedures
• Arthrography/Diagnostic-therapeutic injections
• Facet injections
• Discography
• Vertebroplasty

41. Monitoring
• Fracture healing and status of the implants
• Endoprosthesis
• Effect of treatment e.g rickets, osteoporosis

42. Risks
• Cell death and distorted replication
• Cancers-Thyroid (85% of papillary cancers –radiation related), skin
and breast cancers
• Cataracts
Reducing risk(measures)
• Justify, optimize (ALARA), limit
• PPE
• Scatter
The annual whole body dose equivalent limit for occupationally
exposed persons is 20mSv

43. Take home message
• Imaging is paramount in orthopaedic practice
• Sound knowledge and broad understanding of radiological techniques
as they applied to orthopaedics is paramount for the orthopaedic
surgeons

44. References
• Ramachandran M, Ramachandran N and Saifuddin A. imaging
techniques.
• Berquist TH. Imaging of Orthopaedic Fixation Devices and Prostheses.
• Rockwood and Green’s Fractures in Adults, 9th edition