Transcript Review of indications for imaging: Trauma/ medical/ lodox

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
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Sensitivity
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Specificity
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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
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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.
If the test result is positive, what is the likelihood that the patient will have the condition?
Negative predictive value
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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
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Decision rules
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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
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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:
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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
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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
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Detection papilloedema
Setting of raised ICP
Greater 5 mm
100% sensitive 95% specific
Usefulness ???
Limitations and pitfalls
• Small amounts fluid missed
• Trendelenburg
• Full bladder
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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
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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
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Acute stroke and thrombolytics
Intracranial aneurysm rupture / SAH
Penetrating neck injuries
Vertebrobasilar disease
Capabilities
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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
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Conventional CT / CTA
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Detailed evaluation coronary, pulmonary arteries and aorta
• CAD
• PE
• Aortic dissection
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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
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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
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Lacks sensitivity of CT
No contrast
Portable
Initial study – Abdo pain / vomiting / constipation
Readily demonstrates
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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%