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%