Emergency Department
Imaging - Indications,
capabilities and pitfalls
Dr David Maritz
The Problem
• Rising costs and cost efficient care
• Waiting times
• Ionising radiation
• Must become fully aware of indications, capabilities and limitations,
pitfalls of imaging modalities
• Maximise diagnostic efficiency / improve patient care
Definitions
• Sensitivity
– If a patient has the disease, we need to know how often the test will be positive, i.e.. ‘’positive
in disease’’.
– This is the rate of pick-up of the disease in a test.
• Specificity
– If the patient is in fact healthy, we want to know how often the test will be negative, i.e..
‘’negative in health’’
– This is the rate at which a test can exclude the possibility of the disease.
• Positive predictive value
– If the test result is positive, what is the likelihood that the patient will have the condition?
• Negative predictive value
– If the test result is negative, what is the likelihood that the patient will be healthy?
Overview
• Emergency and critical care imaging
– Bedside ultrasound
– CT
– Radiography
• Decision rules
– Canadian CT Head
– CT Spine
– Knee
– Ankle
– Elbow
– Other ??
1. Bedside Ultrasound
• Improve diagnostic capabilities and guide invasive procedures
• Unexplained hypotension
• Unexplained dyspnoea
• Resuscitative procedures
• Real time imaging
• No ionizing radiation
Cardiac Ultrasound - introduction
• FAST
• Severe hypotension / PEA
• LY dysfunction
• Volume depletion
• Cardiac tamponade
• RV outflow obstruction
• Chest pain, tachycardia, dyspnoea
• Pericardial effusion / tamponade
• Risk stratification in PE
• Acute coronary syndrome
• Left ventricular function
• Sepsis
• Assess preload and LV dysfunction
Capabilities
• High negative predictive value
• Pericardial effusion / tamponade
• Acute valvular emergencies
• Low sensitivity
• ACS
• PE
• Thoracic aortic aneurysm / dissection
• Significant expertise
• Novice limited to identifying:
• Cardiac standstill
• Extent effusion
• LV function
• RV strain
Limitations and pitfalls
• Subxiphoid views
• Obesity
• Abdo trauma / distension
• Parasternal
• Lung hyper expansion
• Physiological pericardial fluid / epicardial fat pad
Abdominal aortic ultrasound - capabilities
• Imaging test of choice for initial detection and measurement
• Accuracy similar to CT
• Rapid
• 95 – 98% sensitivity
• Even by novices
Limitations and pitfalls
• Sensitive for identification of AAA
• Signs of rupture may be absent
• Stable patients – CT follow up
• Unstable patients – surgery
• Hindered by bowel gas / obesity
Trauma ultrasound - introduction
• Extended FAST – blunt and penetrating thoracoabdominal trauma
• Haemoperitoneum
• Haemopericardium
• Cardiac tamponade
• Pneumothorax / Haemothorax
Capabilities
• Accuracies for Haemoperitoneum
• Sensitivities 86 – 94%
• Specificities 98%
• Detection solid organ injury
• IV contrast improves detection (stabilised micro bubbles)
• Free fluid in penetrating injury
• Specific 94%
• Positive predictive value 90%
• Sensitivity 46%
• Haemopericardium – 100%
• Haemothorax – 97% and 99%
• Pneumothorax – 98% and 99%
Capabilities
• Sonographic measurement of optic nerve sheath diameter
• Detection papilloedema
• Setting of raised ICP
• Greater 5 mm
• 100% sensitive 95% specific
• Usefulness ???
Limitations and pitfalls
• Small amounts fluid missed
• Trendelenburg
• Full bladder
• Adiposity
• Bowel gas
• Subcutaneous emphysema
• Pneumoperitoneum
• Rib shadows
• Emphysematous lungs
• Distended painful abdomens
Pelvic ultrasound - capabilities
• Unstable female patients of childbearing age
• Intra-uterine vs. ectopic
• Viability
• Female trauma patient
• Abruption
• Uterine rupture
• Foetal distress / death
• Non-pregnant patient
• Ovarian torsion / tubo-ovarian abscess
Limitations and pitfalls
• Novice limited to
• Diagnosis pregnancy
• Ectopic
• Foetal demise
• Free fluid
• Obesity / bowel gas
• Transvaginal vs. transabdominal
2. CT
CT Head - capabilities
• Emergent CT
• Minor head injury, headache, suspected intracranial infection
• Third generation scanners – fast and sensitive
• Bony injury
• Most acute haemorrhages
Limitations and pitfalls
• Not all SOL – but mass effect and shift seen
• Ischemic stroke – lacks sensitivity early
• Minute amounts blood not seen
• Insensitive for early signs of axonal and cellular injury – mass effect
and oedema seen
• Beam hardening artefact from skull base
CT head neck angiography / perfusion - introduction
• Rapid imaging vascular anatomy
• Identify site of lesion
• Replacing digital subtraction angiography
• Acute stroke and thrombolytics
• Intracranial aneurysm rupture / SAH
• Penetrating neck injuries
• Vertebrobasilar disease
Capabilities
• Carotid artery / circle of Willis
• Rapid 3D data – advantage over catheter angiography
• Visualisation of vessel wall
• Venous rather than arterial access
• More readily available
• Rapid work up needed
• Contraindication to MRI
• Performed immediately after conventional CT
Limitations and pitfalls
• Limited by technical factors
• Radiation dose safe in adults??
• Iodinated contrast ??
• Children ??
CT Chest - introduction
• Conventional CT / CTA
• Detailed evaluation coronary, pulmonary arteries and aorta
• CAD
• PE
• Aortic dissection
• Chest pain??
• Triple rule out
• Single high resolution CTA chest
Capabilities
• Coronary heart disease
• Exceeding 95%
• Pulmonary embolism
• CTA test of choice
• MDCT in 10sec
• Exceeds 90%
• Aortic dissection
• Approaches 100%
Limitations and pitfalls
• CT coronary angiography
• Technical expertise
• Patient factors
• CT pulmonary angiography
• Timing of contrast administration
• Sub segmental emboli may be missed
• CT Aorta
• False positives – motion artefacts
CT Abdomen - introduction
• Abdominal / pelvic pain
• Stable trauma patient
• Sensitivities 69 to 95% / specificities 95 to 100% for bowel mesenteric
injuries
• Bowel obstruction
• Highly sensitive
Capabilities
• Right upper quadrant pathology
• Right lower quadrant pathology
• Left upper quadrant pathology
• Left lower quadrant pathology
• MDCT
• Rapid
• Decreased motion artefact
• +- contrast
Limitations
• Children
• Fat planes less developed
• Radiation exposure
• Obesity
CT Angiography abdomen - Capabilities
• Arterial / venous structures
• Trauma
• 3D reconstructions
Limitations
• Iodinated IV contrast
• Large radiation dose
• Stable patient
• Supine / motionless
3. Radiography
Radiography Chest - capabilities
• Rapid / portable
• Chest pain / dyspnoea / hypotension / thoracic trauma
• Unstable for CT
• Fever unknown source / altered mental status
• Diagnose life threatening conditions
Limitations
• Lacks sensitivity
• Eg PE
• Lacks specificity
• Affected by patient position
• Initial screening examination
• Not be used to exclude dangerous conditions definitively
Radiography Abdomen - capabilities
• Lacks sensitivity of CT
• No contrast
• Portable
• Initial study – Abdo pain / vomiting / constipation
• Readily demonstrates
• High grade bowel obstruction
• Perforated hollow viscus injury
• Volvulus
• Pneumatosis intestinalis
• Additional findings
• Renal / biliary /appendiceal lithiasis
• Vascular calcification
• etc
Limitations
• Poor sensitivity
• Not a definitive study
• Initial exam
• Follow on with CT if non-diagnostic
4. CT head rule
Summary
• Both have sensitivities approaching 100%
• CCHR more specific for identifying need for neurosurgical
intervention 76% versus 12%
• CCHR more specific for identifying clinically important brain injury
50% versus 12%
• CCHR results in lower CT rates 52% versus 88%
5. CT spine
Summary
• NEXUS
• Sensitivity 99.6%
• Specificity 12.9%
• Negative predictive value 99.8%
• Low specificity: ?? Actually increase use of x ray. Therefore
Canadian C-spine rule
• CCR validation - ? Selection bias in study
• Sensitivity 99.4%
• Specificity 45%
• Negative predictive value 100%
• Which rule??
• Further outside validation needed
Groote Schuur Trauma CT neck
6. Knee
Summary
• Pittsburgh
• Sensitivity 99% Specificity 60%
• Reduce x rays by 52%
• Ottawa
• Sensitivity 97% Specificity 27%
• Reduce x rays by 23%
7. Ankle
Summary
• Sensitivity 99%
• Specificity 26 to 47%
• Reduce x rays by 30 to 40%