Intro to Diagnostic Imaging

Procedures that are guided by medical imaging

Fluoroscopy, angiography/angioplasty, stent placement, biopsies, etc

interventional radiology

what type of view?

axial

what type of view?

coronal

what type of view?

sagittal

Using targeted doses of high-energy radiation to kill cancer cells

radiology oncology

radiographs (x-ray/plain films) use what type of radiation?

ionizing

what is remnant radiation?

beam passes through the patient, leftover beam that makes it through the patient

What determines X-ray attenuation?

Tissue density

What captures remnant radiation?

Image receptor

What happens after the image receptor captures radiation?

Information is processed into a viewable image

what is ionizing radiation?

A type of high-energy radiation that has enough energy to remove an electron (negative particle) from an atom or molecule, causing it to become ionized

What is radiodensity?

Combination of physical qualities of an object that determine how much radiation it absorbs from the x-ray beam

in an x-ray, if there is more absorption (high radiodensity), how will the image look?

whiter

what primarily determines radiodensity?

Density and thickness

what is radiographic density?

Amount of radiation that passes through an object (blackening on radiograph)

Relationship between radiodensity and radiographic density?

Inverse

if there is greater radiodensity, there is more/less radiographic density, resulting in whiter/blacker image

less radiographic density; whiter image

Radiodensity categories from black to white?

• Air (black)

• Fat (gray-black)

• Water (gray)

• Bone (white)

X-ray color = air

black

X-ray color = fat

grey-black

X-ray color = water

grey

X-ray color = bone

white

if there is high radiographic density, and low radiodensity, how will the image look? (lighter/darker)

darker

Indication for radiographs after trauma?

Exclude or diagnose fractures

Radiographs are used to assess joint or spinal disease such as?

DJD, spondylosis, scoliosis

Radiographs are used to assess cardiopulmonary disease such as?

Pneumonia (chest X-ray)

Radiographs are used to assess surgical equipment placement such as?

Screws or pins

Radiographs are used to monitor what?

Healing of fractures or surgical procedures

Radiographs are used to screen for what conditions?

Bone tumors, breast cancer, kidney stones, foreign bodies, osteoporosis, enlarged heart

x-rays indicated for assessment of…

• joint or spinal disease

• cardiopulmonary disease

• surgical equipment placement

• heeling progress

How many radiographs are needed for proper evaluation?

At least two images, made as close to 90˚ to each other as possible, are required to view all three dimensions

# and orientation of images taken typically depends on?

body part

Common radiographic projections?

AP, lateral, oblique

Advantages of radiographs?

• Fast, inexpensive, low radiation

• excellent bone detail

• screens many pathologies

• helps guide next imaging study

Main limitation of radiographs?

show only significant bone density changes → some may not be observable until later stages (osteoporosis, avascular necrosis, stress fractures)

Why might some fractures still be missed even with 2 views?

bone thickness can obscure areas (e.g., tibial plateau fx)

what are not well-defined on an x-ray?

soft tissues

What does CT merge?

X-ray with computer processing

How does CT work?

x-ray beam and detector system rotate in an arc around patient → computer reconstructs data into an image

What does each CT image represent? how thick?

Axial cross-sectional slice 0.2-1.5 cm thick

Why are multiple CT slices viewed together?

To evaluate dimensions of a structure

What do newer CT technologies allow?

Multiplanar (sagittal, coronal) and 3D images

what are the 3D images from a CT scan called?

reformations

Modality of choice for neuroimaging in acute/trauma settings?

CT scan

CT primarily for the evaluation of…

• Loose bodies within a joint

• Degenerative changes within the spine

• Spinal stenosis, exp if combined with myelogram

• Soft tissue processes like cellulitis or abscesses

indications for CT scan

High-risk trauma patients (initial examination) at thorax, abdomen, and pelvis (TAP) → assess for life threatening injuries

Identification of subtle and/or complex fractures

what types of fractures are best for CT scan?

Subtle or complex

Advantages of CT?

• Detailed anatomy/pathologic processes

• faster than MRI/US

• cheaper than MRI

• better for claustrophobic patients

Main disadvantage of CT?

• Higher radiation dose

• less soft tissue contrast than MRI

• Patient movement or metal implants can produce artifacts

What happens to radiation that passes through the patient?

It is collected to make an image

What is effective radiation dose? measured in?

Amount of radiation absorbed by patient

millisieverts (mSv)

What principle guides radiation safety in imaging? its purpose?

ALARA (As Low As Reasonably Achievable)

Every effort is made to decrease radiation risk

how can you tell T1 and T2 weighted images apart?

T2 = find a structure that has a lot of water in it, see if its the lightest/whites thing in the picture

what imaging technique is used in MRI?

cross-sectional

What does MRI use to generate signals?

magnet orients protons in a specific direction, radio frequency shifts them away from magnet

realignment of protons releases energy, which the MRI measures

what does MRI stand for

magnetic resonance imaging

how does MRI work?

1. magnetic field is used to align hydrogen protons

2. radio frequency waves are absorbed by protons and then emitted as a signal

3. a radio frequenting coil picks up the signal and transmits it to the computer

4. computer processes the data and an image is generated

Why do tissues appear different on MRI?

resonate at different radiofrequencies

MRI signal intensities of tissues differ based on ____

composition

What does MRI sequence mean?

timing of the radiofrequency pulse and the capturing of the energy signal

Why are multiple MRI sequences used?

compare how the tissue appears in different sequences to help with diagnosis

Most common MRI sequences?

T1 and T2 weighted

What does MRI T1 sequence show best?

resolution of anatomy

What does MRI T2 sequence show best?

Signal from water is brightest

what MRI weighted sequence is most valuable for identifying pathology that has a component of inflammation/edema?

T2

what is hypo-intensity on an MRI?

less bright than surrounding structures

What contrast medium is commonly used in MRI?

Gadolinium

why would a contrast medium be needed in an MRI?

Improved resolution in tissues when evaluating blood vessels, possible tumor, infection, or inflammation

MRI indications

• Soft tissue injuries, especially to ligaments and tendons

• Diagnosis of bone tumors, stress fractures, osteomyelitis, and avascular necrosis

• Evaluation of intervertebral disc pathology

why is MRI indicated for looking at bone?

Can be revealed in the early stages due to sensitivity of MRI to detect bone marrow changes

MRI contraindications

• Cardiac pacemakers

• Ferromagnetic aneurysm clips

• Metal foreign bodies in eyes/orbit

• Cochlear implants

• 1st trimester pregnancy

main advantages of MRI

• Excellent resolutions of all soft tissues

• No ionizing radiation

main disadvantages of MRI

• Poor for imaging bone (due to limited water content)

• Is expensive, time consuming

• Claustrophobia is an issue

Nuclear medicine procedure using radioactive tracer to diagnose the severity of a variety of bone diseases and conditions

Skeletal Scintigraphy (Bone Scan)

bone scan primarily looks at what bones diseases and conditions?

fractures, infection, and cancer (esp. metastasis)

how does bone scan work?

radioactive tracer adheres to metabolically active bone (hot spots)

Bone scans being replaced by _____ as they may be more sensitive and specific

PET scans

Enhanced form of a radiograph that is used to measure bone loss and bone mineral density

Gold standard for diagnosing osteoporosis

Dual Energy X-ray Absorptiometry (DEXA or DXA)

how does DXA machine work?

sends x-rays with two distinct energy peaks through the bones being examined

soft tissue amount can be subtracted from the total and what remains is a patient's bone mineral density

in DXA machine, what are the energy peaks absorbed by?

one by soft tissue, other by bone

Cross sectional imaging technique based on the reflection of sound waves off tissue interfaces

diagnostic MSK ultrasound

diagnosis MSK US indications

• Soft tissue pathology, particularly in sports injuries including tendon and muscle tears

• Evaluation of fluid collection, including cysts, bursas, synovitis, infections, inflammation

• Assessment of articular cartilage

• Evaluation of nerves for inflammation or entrapment

advantages of MSK US

• Low cost, portable

• image soft tissue in the presence of hardware

• Easy to compare to opposite side of body

• Able to include dynamic movements and/or stress tissues

disadvantages of MSK US

• Operator dependent → need STRONG anatomy knowledge

• US does not penetrate bone, cannot see some intra-articular ligaments

• Time consuming

• Can be difficult to image patients who are obese

ABCs of radiologic analysis

A: Alignment

B: Bone Density

C: Cartilage Spaces

S: Soft Tissues

what is the purpose of search patterns in radiography?

methodology for looking at an image in an organized fashion

Helps to ensure that everything possible to observe has been visually accounted for

ABCS: alignment evaluates?

• skeletal architecture

• contour of bone

• bones to adjacent bones

ABCS: bone density evaluates?

• textural abnormalities

• local bone density changes

ABCS: cartilage spaces evaluates?

• joint space width

• subchondral

• epiphyseal plates

ABCS: soft tissues evaluates?

• muscles

• fat pads, fat lines

• joint capsules

• periosteum

• misc. findings

open mouth films look at?

C1/C2 instability

flexion/extension films look at?

Atlantodental interface >3mm indicates instability (C1/C2 subluxation)

search pattern for MRI (ABCDS)

A = alignment of anatomy

B = bone signal

C = cartilage

D = edema

S = soft tissues and synovial tissue

MRI ABCDS: bone signal looks at?

altered signal in bone MARROW. Can also assess for tumors, cysts, or avascular bone

MRI ABCDS: alignment of anatomy looks at?

Assess the alignment and continuity of ligaments, nerve, and muscles

MRI ABCDS: cartilage looks at?

Assess for osteochondral or articular cartilage abnormalities or tears (e.g. labral, meniscus, TFC)

MRI ABCDS: edema looks at?

”footprint” of injury.

On T2 images, look for edema due to inflammation

what are the 4 validated clinical decision rules?

• Ottawa Ankle Rules

• Ottawa Knee Rules

• Pittsburgh Rules for Knee Trauma

• Canadian C-spine Rule

purpose of clinical decision rules in radiology

• Standardize care among first-contact providers

• Reduce unnecessary radiologic imaging

• Identify injuries that should be evaluated by radiograph

Pittsburgh Rules for Knee Trauma

blunt trauma or fall mechanism of injury AND

• age under 12 or over 50 AND/OR

• inability to walk 4 WB steps in the ED