Diagnostic Radiology: Imaging For Chest Pain

Question 1

Imaging modalities for chest pain

Answer 1

1. CXR
2. CT
   - Coronary CT angiogram
   - CT Pulmonary angiogram
   - CT Aortogram / Thorax with arterial phase
3. USG / Echocardiography
4. Nuclear imaging
   - VQ scan
   - Myocardial perfusion imaging (with SPECT)
5. MRI
6. Interventional imaging
   - Catheter coronary angiography
   - Pulmonary angiography

Question 2

1. CXR

Answer 2

Indications:

• Pneumothorax
• Mediastinal abnormalities / Injury (e.g. Aortic dissection)
• Skeletal injury (e.g. Rib fractures)
• Chest infection

Advantages:
- Quick + Easily available

Disadvantages:

• Abnormalities not visible at all
• Subtle abnormalities missed
• Difficult to interpret (one of hardest even for radiologist!)

Question 3

2. CT

Answer 3

3 Types of CT:

1. Coronary CT angiogram (but will miss most of upper half of lungs)
2. CT Pulmonary angiogram (CTPA: assess pulmonary arteries for PE)
3. CT Aortogram / Thorax with arterial phase (assess aorta / lung abnormalities for malignancies)

Advantages:

• Higher sensitivity + specificity than CXR (i.e. abnormalities on / not on CXR is visible on CT)
• Fast image acquisition (whole body <2 secs)

Disadvantages:

• More radiation
• Coronary CT has high rate of false positives for significant coronary artery disease if the patient has a lot of calcified atherosclerotic plaques

Strengths:

• Almost every pathologies which cause chest pain (e.g. Coronary artery disease, Pulmonary embolism, Acute aortic syndromes etc.)
• Excellent at ruling out Coronary artery disease

Weakness:

• Suboptimal cardiac function assessment (weaker than Echo / MRI)
• Suboptimal heart muscle characterisation (e.g. infarcted myocardium / fibrosis in hypertrophic cardiomyopathy / function) (weaker than Nuclear scan / MRI)

Question 4

3. USG / Echocardiography

Answer 4

Echo:
- Lie on left lateral position

Advantages:

• No radiation
• Quick + easily available + cheap

Disadvantages:

• Any gas / calcium / metal-containing structure is difficult (∵ most USG beam reflected back —> no USG beam penetrate deeper —> cannot create image of deeper structures)
• Operator dependent
• Limited by acoustic windows (i.e. Intercostal spaces) —> Difficult to perform in patients with Chest wall deformities, COPD, Obesity
• Limited myocardial tissue characterisation

Strengths:

• Characterise cardiac function (+ some ability to assess myocardial tissue)
• Coronary artery disease (Stress echo) —> assess change in contractility of myocardium (BUT lower sensitivity in diagnosis than other modalities)
• Lower limb DVT (incompressible vein indicate DVT)
• Pleura (e.g. effusion)

Question 5

4. Nuclear imaging

Answer 5

Indications:

• PE (VQ scan)
• CAD (Myocardial perfusion (MPI) scan)

MPI:
- Run on treadmill / bicycle / pharmacological agents
—> Achieve adequate physiological stress response
—> Inject radioactive tracer
—> Picked up by heart
—> Agent not present in myocardium affected
—> Gamma camera after 20-40 mins (patient lie for 15-20 mins in scanner)
—> Good for identifying infarcted myocardium

VQ:
- Breathing in of radioactive tracer to assess ventilation

Advantages:

• Ideal for pregnant women compared to CTPA (∵ lower radiation dose to breast (∵ increased radiosensitivity during pregnancy))
• Well established modality
• MPI has robust prognostic data

Disadvantages:
- MPI: Lower diagnostic accuracy (DOR, AUC) compared to MRI / CT
- If patients have abnormal CXR
—> VQ scans will likely to be indeterminate
—> ∵ VQ scans also assess both ventilation + perfusion
—> areas with ventilation / perfusion defect cannot show other abnormalities (e.g. PE)
—> ***VQ scans should NOT be performed unless no other options
- Difficult to perform in haemodynamically unstable patients (i.e. Low BP, High HR, High RR)
- Higher radiation dose (esp. to fetus) (4-5 times higher than background radiation of a whole year)

Question 6

5. MRI

Answer 6

Types:
- Stress Cardiac MRI
—> Highly accurate modality to assess CAD (~ to Nuclear MPI)
—> Use Adenosine / Dipyridamole
—> Vasodilation
—> Stress the heart
—> Gadolinium contrast to assess myocardial perfusion defect

Advantages:
- Highest diagnostic accuracy, sensitivity, specificity of all modalities
- Higher spatial + temporal resolution
- No radiation
- Good for cardiac function assessment
—> Excellent myocardial tissue characterisation (e.g. infarct, myocarditis)
—> Excellent diagnostic accuracy for myocardial ischaemia
- Able to assess Pulmonary arteries + Aorta
- Able to create 3D images

Disadvantage:

• Claustrophobia
• Most sequence require breath-holding otherwise images will have breathing artefact
• Long examination time (>=30 mins) (∴ unsuitable for uncooperative patients)
• Lung images not as good as CT (∵ slightly inferior spatial resolution)
• Able to assess for PE but only in limited sites + take much longer time than CTPA
• Expensive + limited availability

Question 7

6. Interventional imaging

Answer 7

Catheter inserted into desired location
—> Iodine contrast (same as CT) injected
—> Fluoroscope (use X-ray but more mobile than X-ray tube) to obtain ***live images

Advantages:
- Therapeutic (e.g. Stent insertion, Embolectomy)
- Used to be gold standard for coronary artery assessment —> now replaced by **fractional flow reserve (FFR) (same procedure but pressure wire is included —> placed across site of narrowing —> determine pressure difference —> determine the functional significance of coronary artery narrowing during rest / pharmacological stress —> if ratio **<0.8: significant narrowing —> interventional procedures e.g. stenting)
- High accuracy for assessment of pulmonary arteries (e.g. PE) but largely redundant now due to CTPA (∵ non-invasive + high accuracy)
—> now only for therapeutic procedures e.g. Catheter-directed thrombolysis, Embolectomy

Disadvantages:

• Risk of complications e.g. stroke, MI, vessel rupture, dissection
• Expensive
• Radiation

Indication:
- Only chosen when diagnosis confirmed by other modalities