week 2 prework + advanced imaging slides

Cost and Radiation Compairisons

conventional radiographs = $450 and 1.5 mSv

CT = 2k and 6.0 mSv

MRI = 3.5k and no radiation

bone scan, whole skeleton = 1.4k and 6.3 mSv

CT Overview

Computed Tomography

creates images using multiple x-rays in cross-sectional (axial) slices from different projection angles

the beam rotates around the body, multiple projections pass through and an electronic detector array records the patterns of densities

CT scanner

motorized table moves the pt through a circular opening

x-ray source and detector assembly within the system rotate around the pt

• one rotation is ab 1s

• during rotation x-ray source produces a narrow, fan-shaped beam of x-rays that passes through a section of pt body

scout image

2d digital radiograph produced by CT scanner

used to localize the structures to be scanned

• orientation and good for planning purposes

CT planes

coronal, axial, sagittal

same for MRI

CT image

reflects tissue radiodensity without superimposition of other tissues

some loss of resolution due to volume averaging when there is an image with tissues that lie proximate or over each other

viewer sees several images/slices

images can be windowed to reduce the range of radiodensities displayed and focus on a particular tissue

Slice thickness

• is anatomy dependent

• can range from .5-2 mm for small joints and 2-3 mm for large

• thinner slices means image volume is smaller

  • less radiodensity and increased noise

  • greater radiation to produce the same image quality

Additional Forms of CT

3d CT - multiplanar reconstruction

CT myelogram - injection of contrast material into the spinal fluid

Cone Beam CT - often used in dental practice - single volume of data means shorter scanning time and less radiation

CT benefits

best for identifying subtle fractures and/or complex fractures

best for evaluating degenerative changes

first choice for trauma - images osseous and soft tissues structures

excels in evaluation of spinal stenosis - especially if performed as a CT myelography

combined with diskogram = gives condition of intervertebral disk

best modality for evaluation of loose bodies in a joint

less time consuming (MRI and ultrasound) and less expensive (MRI)

allows for accurate measurements of osseous alignment in any plane

less problematic for pt with claustrophobia

CT limitations

limits the exam based on radiodensity

radiation exposure

CT roughly 4x single radiograph dose

CT in other medical specialties

Neuroimaging - best modality for acute settings, and a ‘head CT’ is standard protocol in trauma for immediate assessment of intracranial bleeding

cardiac imaging - CT angiogram

Pulmonary imaging

CT report

levels imaged

contiguous or interrupted slices

slice thickness

reformatting/reconstructions

angulation of gantry

windows provided

use of contrast agent

MRI overview

no ionizing radiation

processes to create image:

• signal generation based on the properties of magnetic resonance

• relaxation processes

• signal detection

• encoding of spatial information

• reconstruction of the image from the signal

• manipulation of tissue-dependent contrast

MRI Hardwar schematic

magnet

gradient coils

RF coils - to transmit and receive

MRI science

hydrogen atoms in the body have magnetic moment

external magnets produce resonance from each proton in the hydrogen atom

machine detects proton’s position/signal and takes a ‘photo’ of the hydrogen molecules in the body and then digitizes it into an image of the body part

T1 weighted = captures early signal decay

T2 weighted = captures late stage of signal decay

before imaging - hydrogen protons are aligned in random directions

superconducting magnet creates a strong magnetic field aligning protons in same directon

radiowaves are transmitted through body and the waves jostles the protons a bit off their axis and spin them in the same direction

radiowaves = turned off, protons return to aligned positions; time it takes ions to return to alignmen is measured by scanner → different issue shave a unique time frame

computer uses data to assemble a detailed image of body

T1 weighted image

bone marrow gives rise to relatively high signal intensity

CSP gives rise to low signal intensity = dark

T2 weighted image

CSF shows high signal intensity

MRI protocols

sequence for MRI - not standard like in radiography

spin-echo (SE): T1 and T2 imaging

Gradient-echo (GRE) sequences

• fast image acquisition

• high resolution and thin slices

• high contrast between fluid and cartilage - depends on parameters

MRI Open Scanner Advantages

greater ability to scan claustrophobic or obese pt

reduction of scanning noise

possibilities of performing tests or procedures during scanning

MRI Open Scanner disadvantages

lower field strength → requiring adjustments of imaging sequences

lower signal-to-noise ratio

longer scanning times

can be more fuzziness due to more pt movement

MRI upright scanner advantages

ability to examine the spine under weight-bearing conditions → spine looks different than while sitting or laying down

ability to scan pt. who are to large to fit into the bore of the magnet or must be scanned in the upright position becuase of conditions such as CHF or severe thoracic kyphosis

MRI upright scanner disadvantages

longer scanning times (3x than conventional high-field scanner)

possible image degradation due to longer scanning times and lower field strength

placement of pt in a painful position which may lead to increased pt. movement during examination and degraded image quality

MRI clinical use

good at finding changes and variations in bone marrow

• differential diagnosis of bone tumors, stress fractures, and avascular necrosis

good soft tissue detail - tendons, ligaments tears, meniscal tears

best modality for evaluation of disk herniations and other potential causes of nerve root involvement

ability to stage neoplasms in bone and soft tissues as well as evaluate extent of tissue invasion prior (and after) to surgery

CT and radiograph similarities vs differences

similarities:

• employment of x-rays which are attenuated by body tissues

• radiodensities are similar in color

differenes:

• CT creates images based off of cross-sectional axial slices

  • comes from projections at many different angles

CT planes

coronal, sagittal, axial

windowing

the range of radiodensities which are displayed in an image

What does CT do best?

identify subtle fractures and/or complex fractures

detailed evaluation of degenerative changes (ex. spinal arthritic changes)

can determine both osseous and soft tissue structure injuries = good for trauma

excels in the evaluation of spinal stenosis

gives invaluable information of the condition of an intervertebral disk when combined with a diskogram

best modality for evaluation of loose bodies in a joint

less expensive and time consuming and problematic (claustrophobia) than MRI

CT limitations

ability to determine histologic makeup of imaged tissues - due to radiodensities

relatively high radiation exposure

T1 Weighted image

there is a short time to repetition and time to echo

time to repetition

the time at which the radiofrequency pulse is repeated to again displace the protons

time to echo

the time at which the signal is captured

T2 weighted image

there is a longer time to repetition and time to echo

made at lower energy levels = grainer and less spatial resolution

what does MRI image best?

displaying soft tissues in detail

• ex. difference between partial and full tear of tendon/ligament

very sensitive for detecting changes in variations in bone marrow

• helpful with bone tumors, stress fractures, and avascular necrosis

best modality for evaluating disk herniations or other potential causes of nerve root impingement

ability to stage neoplasms in bone and soft tissues while evaluating the extent of the tissue invasion

MRI limitations

imaging cortical bone - due to low signal intensity

more time needed to produce image

costs more

MRI contraindications

femmormagnetic surgical clips can be displaced → brain aneurysm clips = fatal hemorrhage

orthopedic hardware can cause image distortion

MRI health concerns

possible malfunction of pacemakers (within or near magnetic field)

claustrophobia = ~10% of pt.

the need to sedate pt if not able to stay still (children)

MRI advantages over CT

greater contrast resolution for soft tissue imaging

greater ability to image organs surrounded by dense bone structures

non ionizing radiation

less risk of missing disease processes due to having multiple sequences going through

MRI disadvantages

more expensive

not widely accessible

slower imaging times

more operator time involved with selecting imaging parameters

wider slices of imaging

more loss of image quality as a loss of motion

less power of resolution when imaging cortical bone

harder to image individuals with metal implants

hyperechoic

structures which reflect a lot of energy with reference to surrounding structures

waves reflected off hyperechoic tissues and interfaces between tissues dissimilar in density have high amplitude and produce bright images

hypoechoic

structures which reflect little energy than other surrounding structures

waves reflected off hypoechoic tissues have low amplitude and produce a dark image

Anechoic

structures which reflect no energy

Ultrasound advantages over MRI

higher resolution

portability

lower cost

no known hazards

ready comparison with opposite side

ability to follow a structure from beginning to end regardless of orthogonal plans

ability to modify imaging while it is being performed, palpating for the area of tenderness and performing examination procedures during the imagins

provides intricate details of muscles internal architecture

can demonstrate tendon internal architecture clearly showing the fibers

• can reveal pathological changes (degenerative changes, longitudinal tears)

Ultrasound disadvantages

limited field of view due to limited size of transducer

more dependent on operator

doesn’t penetrate the cortical outlines of bone = structures deep to bone are not visualized

does not cross air interfaces

obese pt are not imaged well

Additional MRI Studies

MR Arthrography

• gadolinium in iodine is injected into joint and creates bright signal → allows the radiologist to see small defects in capsule, articular surfaces, ligaments, or labra

MRI Myelography

• MRI study of the spinal canal and subarachnoid space using high resolution MRI with strong T2 weighting

• no use of contrast material

Advantages of CT over MRI

less expense

greater availability

faster imaging times

less operator time involved in selecting imaging parameters

thinner slice

less loss of image quality owed to motion

greater power of resolution when imaging cortical bone

easier imaging of individuals with metal implants

Ultrasound in PT

therapeutic:

• tissue healing

• pain management

Diagnostic:

• imaging

• rehabilitative ultrasound imaging - real time application

rehabilitative ultrasound imaging (RUSI)

a procedure used by physical therapists to evaluate muscle and related soft tissue morphology and function during exercise and physical tasks

used to assist in the application of therapeutic interventions aimed at improving neuromuscular function

ultrasound equipment

pulser

transducer

scan converter and monitor

ultrasound pulser

produces waves of electrical energy in frequency range of 2-15 MHz

ultrasound transducer

converts electrical waves to sound energy

delivers waves to tissue

receives reflected waves and converts them back to electrical energy

ultrasound image based on reflection of sound wave

amount of reflection determined by:

• degree to which the tissues reflect sound waves

• difference in acoustic impedance of tissues at interface (large difference result in more reflection)

• smoothness of the reflecting interfaces - smooth cortical outlines reflect more than irregular outlines

  • angle of reflection (more the angle deviates from the perpendicular, the less the energy reflected back to the ultrasound transducer

echogenicity

degree to which the tissues reflect sound waves

refraction amount depends on:

difference in acoustic impedance between the two tissue types

angle of incidence

angle of incidence

the farther from the perpendicular, the greater the refraction

doppler ultrasound

measures blood flow in an artery or vein

• can demonstrate presence and direction of blood flow

• can identify gross circulation anomalies

• cannot provide detailed information about the overall flow into an area

based on principle: can measure velocity of blood cells

• sound waves reflected off blood cell moving TOWARD transducer arrive at the transducer at a higher rate than corresponds to the frequency of the emitted waves

  • sound waves reflected off blood cells moving AWAY FROM transducer return at a lower rate

ultrasound planes

relative to the structure being examined

longitudinal or transverse

ultrasound and tissues

bone - not penetrated

• bone-soft tissue interface (tendon/ligament): bright echo

• subcortical bone: hypo or anechoic (dark)

tendon - hyperechoic relative to muscle

ligament - hyperechoic relative to muscle

muscle - hypoechoic relative to fascia or tendons

bursa - hypoechoic line

hyaline cartilage - hypoechoic layer

fibrocartilage - hyperechoic

nerve - hypoechoic to tendon, hyperechoic to muscle

ultrasound: Coritcal bone

normal = hyperechoic, smooth, continous

abnormal = break in continuity, uneven surfaces

ultrasound tendons/ligaments

normal = hyperechoic; distinct parallel fiber pattern

abnormal:

• strains: thickening, of mixed echogenicity (hypoechoic if inflammation or hematoma); disrupted fiber pattern

• ruptures: disruption of structure, initially filled with hypoechoic hematoma and separation of ends

ultrasound muscle

normal: hypoechoic with parallel fibrous hyperechoic bands

abnormal:

• muscle strain - disruption of fibrous bands; hypoechoic hematoma in early stages

• rupture: retraction of muscle

ultrasound bursa

normal = thin hypoechoic line

abnormal = increased width of bursa; in later stages hyperechoic thickening of bursa walls

ultrasound hyaline cartilage

normal = hypoechoic layer next to cortex

abnormal = early changes display as inhomogeneous thickening; later irregularity and disruption

ultrasound nerve

normal = hyperechoic, relative to muscle

abnormal = flattening; swelling proximal to compression

ultrasound cysts

normal = anechoic

abnormal = increased volume, thickened walls; septations; debris