3. Radiology Of MSK Flashcards
Parts of musculoskeletal system
- Bones
- Soft tissue
- Cartilage
- Muscle
- Ligaments
- tendons
Examples of damage to tissues
- Break/tear
- Chronic wear and tear/ degernate
- Infection
- Primary cancer or metastases
Factors which determine which Imaging Modality to use
- Type of tissue
- Suspected injury- from clinical history
- Age/radiation exposure
- Previous imaging
Xray basic process
X ray source at one side of patient – detector on other side
• X rays travel through patient to hit detector
• X rays reach detctor = black
• X rays hit something dense = deflected x rays = white
Xray radiograph
Radiograph is a projectional image generated by passage of x-rays through an object (Patient in case of medial radiograph).
Image is generated on a detector plate called x-ray detector.
Detector plate is like a photographic film, when x-rays hit the plate, it turns black.
Amount of blackness depends on the number of x-rays hitting the plate. X-rays travel in straight line.
X-rays are stopped by materials with lot of electrons/dense materials like bones, metals etc.
Advantages of xrays
- X-rays are quick.
* X-rays are readily available and inexpensive.
Disadvantages of xrays
- Involves radiation.
- 2D Image to look at 3d structure
- Poor soft tissue information.
Uses of xrays in msk
Skeletal trauma/ acute bone or joint injury
- fractures
- joint dislocation
Evaluation of chronic bone or joint pathologies
- chronic osteomyelitis
- chronic joint arthritis
- chronic septic arthritis
CT scan
CT scan Computed tomography (CT) scanning, also known as computerised axial tomography (CAT)scanning, is a diagnostic imaging procedure that uses radiation to build cross-sectional images (“slices”) of the body CT scan provides thin sections of the musculoskeletal system.
CT scan images
Thin slices give detailed information about the bone structure and pathology. Soft tissue detail is better than plain radiographs.
Whole body CT can be performed in short time (few minutes) to look for bone or soft tissue injury. Subtle un-displaced fractures are better seen on CT scan.
Spinal fractures and other complex fractures like pelvic fractures are seen in great detail. Slices can be reformatted to give 3D construction. - used in surgery
CT scan advantages
Cross-sectional. Thin slices of the body.
Excellent in assessment of complex bone trauma.
Fast.
Multiplaner and 3D reconstruction.
CT disadvantages
Involves significant radiation.
Poor soft tissue detail (better than Plain radiograph)
MRI
Non invasive method of mapping the internal structures of the body.
Utilizes magnetic resonance of the hydrogen nuclei to produce high quality cross-sectional images of the body in any plane.
There is no use of ionising radiation.
It utilizes radio frequency waves in presence of carefully controlled magnetic field.
MRI
Two fundamental objectives
- Definition of normal anatomy
* Detection of pathology (Abnormal fluid/ enhancement)
Uses of MRI
—> MRI is used for assessment of bones, joints and associated soft tissue like ligaments and tendons.
• MRI is better than CT and X-ray in assessment of the soft tissue.
• MRI is used in assessment of MSK infection like osteomyelitis, soft tissue infection and septic arthritis.
• MRI is poor in showing micro-structure of the bone.
Two types of sequences
MRI
- Anatomy defining sequences: T1, Proton density
* Fluid sensitive sequences: STIR or PD Fat Sat
Anatomy defining sequences: T1, Proton density
–> Normal muscle is termed as Isointense (Signal intensity) SI .
Things that look Bright on T1 (Hyperintense)
- Fat
- Gadolinium
- Proteinaceous fluid
- Hemorrhage.
Things that look dark, Low on T1 (Hypointense)
- Fluid
- Tendons, ligaments.
- Cortical bone
• Fluid sensitive sequences: STIR or PD Fat Sat
STIR (Short tau inversion recovery)
PD Fat Sat T2 Fat Sat.
All the signal is lost except fluid and oedema signal.
Barring few exceptions most of the MSK pathologies appear BRIGHT on Fluid sensitive sequences
T2
- Fluid is hyperintense (Bright) VERY IMPORTANT – fat is not bright onT1
- Fat is hyperintense (Bright)
- Tendons, ligaments, cortical bone are hypointense (Low)
- Old haemorrhage gives low signal.
MRI advantages
- Excellent for imaging of soft tissue structures like ligaments, tendons and muscles.
- Detailed anatomy of joints.
- Excellent for bone marrow imaging
MRI disadvantages
- Scan takes long time 45 to 60 min. Patient has to stay still in the tunnel.
- Noisy environment.
- Claustrophobic patients can’t tolerate the scan.
- Non-Compatibility with metallic /electronic devices like pacemakers.
MRI safety
—> Magnetic field in an MRI is stronger than those used industrially to move cars.
Ferromagnetic metals are not compatible
• Iron
• Nickel
• Cobalt
Most of the electronic devices are not compatible.
MRI saftety website tells you what devices are compatible and non compatible
Ultrasound
Ultrasound is used for imaging of soft tissue.
Ultrasound if good at finding fluid collection/haematomas or Joint effusions.
It is also good for assessment of the tendons and muscles e.g. if there is suspected achilles tendon rupture, an US of achilles tendon will help to confirm this.
* There is no radiation involved. * Ultrasound is not good for assessment of the bones or deeper structures.
Ultrasound
Advantages
No radiation involved. No known contraindications/adverse effects.
• Excellent soft tissue resolution for superficial soft tissue.
• Excellent imaging modality for assessment of tendons and peripheral nerves.
• Fluid collections.
• Superficial foreign bodies.
• Dynamic imaging.
• Excellent for image guided MSK intervention. = eg. See needle under ultrasound guidance
Ultrasound
Disadvantages
- Operator dependent.
- Poor deep tissue resolution.
- Limited bone and intra-articular imaging
Bone scan – radioisotope
- Patient is emititng radiation
* Patient is injected with radioistope that is taken up in more metabolic areas ((cancer cells)
Nuclear imaging
—> Radioisotope-labelled, biologically active drugs that are administered to the patient to serve as a marker of biologic activity.
Nuclear imaging - uses
They are used to assess areas of metabolically active bone such as when trying to localise:
• Bone-forming metastatic lesions.
• Healing fractures.
• Areas of osteomyelitis.
