Clinical imaging of the Thorax

Question 1

How do standard X-rays work?

Answer 1

• A beam of energy is aimed at the body part being studied
• A plate behind the body part captures the variations of the energy beam after it passes through the various organs of the body, having diff densities , e.g. skin, bone, muscle, tissues etc

Question 2

Compare density and appearance of X rays

Answer 2

Air - appears the blackest - absorbs least X rays
Fat - Grey , blacker than soft tissue
Fluid/soft tissue - Both fluid (e.g. blood) and soft tissue (e.g., muscle) have the same density on conventional radiographs
Calcium - The most dense, naturally occurring material (e.g. bones) : absorbs most x rays
Metal : Usually absorbs all x rays and appears the whitest (e.g., bullets barium)

Question 3

What are the different X-ray techniques?

Answer 3

Different views:
- PA, AP, Lateral, Oblique
- Distance between the X-ray tube and the patient is between 30 to 38 cm
- Patient needs to be stable
- Scapulae should be retracted

Question 3

What are the advantages of plain radiographs?

Answer 3

• Quick, cheap, low-dose radiation , can be portable, can detect many pathologies, can be done anywhere

Portable, quick , can be done anywhere , One shot, no standardisation of distance

Question 4

What should a good full inspiratory chest radiograph films look like?

Answer 4

• 9-10 posterior parts of the ribs should be visible
• When X-ray beams pass through the anterior chest wall on to the X ray plate (AP view), the parts of the ribs , closer to the film (i.e.,, posterior parts of the ribs ) are most apparent
• Good inspiratory CXR should show 6-7 anterior parts of the ribs intersecting the diaphragm in the mid-clavicular line

Question 4

What are the different X ray techniques (PA vs AP)?

Answer 4

Posterior- Anterior (PA) is the standard/ conventional projection
- PA views are of higher quality and more accurately can assess the heart size than AP images
- Heart relatively near the detector

PA and AP views are viewed as if looking at the patient from the front (Left and right sides opposite)

PA projection not always possible. AP projection , the heart size is exaggerated because the heart is relatively further away the detector, and also because the X ray beam is more divergent as the source is nearer the patient

Question 5

What does an under-penetrated CXR cause?

Answer 5

• Increase likelihood of missing an abnormality in the the overlying structures; the thoracic vertebrae - not clearly visible
• Over-penetrated CXRs - diffusely dark ; pulmonary markings absent/ decreased ; pneumothorax, consolidation or emphysema may be missed
• Milliampere-seconds (mAs) - a measure of radiation produced (milliamperage) over a set amount of time (secs)

Question 6

Explain what you need to observe in a Chest PA/ X ray

Answer 6

• Size of cardiac shadow
• Shape of the heart shadow
• Cardiac diameter : If max cardiac diameter is >1/2 of max thoracic diameter , suggests an enlarged heart
• AP view films make the heart appear larger than it actually is (false magnification of the heart)
• Look out for heart features, pulmonary arteries, ribs , liver etc

Question 7

What are some structures to remember when doing chest radiographs?

Answer 7

• Aortic knob/knuckle should be visualised in the normal chest radiography around the level of t4/5 or just lateral to the carina
• The costo-phrenic and costo-cardiac angles should be sharp and well defined. Blunted/ lost = chance of presence of any kind of fluid in the pleural cavity
• Bowel perforation - if free air is found under right hemi-diaphragm (Normal gastric bubble, seen under left hemidiaphragm - shouldn’t be confused)
• Any deviation of the trachea from the midline could suggest the Prescence of a mediastinal mass or Prescence of tension pneumothorax

Question 7

What are some things to observe in Radiography?

Answer 7

AIRWAYS: Trachea, endotracheal tube etc
BONES : Clavicles, ribs, sternum, thoracic vertebrae
Cardiac shadow
Diaphragm
Everything else : Any wire, tubes, pacemaker, effusions

Also check :
- Apices and hila of the lungs (identical size, shape and density of hila ; left hilum is higher than right)
- Broncho-vascular markings
- Behind the heart
- Costo-phrenic angles
- Diaphragm - look below it (right hemi-diaphragm is higher than the left)
- Soft tissues (like the breasts, any tumours, etc.)

Question 8

What is a CT scan?

Answer 8

• diagnostic imaging procedure; uses x rays and computer technology to produces internal body images
• Shows detailed images of any part of the body, including bones, muscles, fat, organs and blood vessels
• Can diagnose tumours, investigate internal bleeding or check for other internal injuries
• Also used for tissue or fluid biopsy

Question 9

What is Magnetic resonance imaging (MRI)

Answer 9

MRI - diagnostic modality capable of producing both anatomic and physiologic data that utilises the molecular composition of tissues, especially generate images with extraordinary contrast between soft tissues
- MRI can assess functions of heart’s chambers, thickness of heart walls, extent of damage from MI, aortic aneurysms, blockages in blood vessels, joint abnormalities, torn cartilages or ligaments, IV disk abnormalities etc

Question 10

What are some CT scan advantages compared to MRI?

Answer 10

CT:
- less expensive
- quicker to perform than MRI scans
- Used for speedy diagnosis in emergency situations
- can identify internal bleeding, tumours, cancer development and fractures
- The whole body of a person, doesn’t need to enter the CT scanner, so the patients don’t feel claustrophobic

Question 10

What are some advantages of MRI scans?

Answer 10

• can produce more detailed images than CT scans
• MRI scans - do not use radiation
• Much safer to use
• MRI images can identify pathologies in the soft tissues, joints, organs, brain and heart better than the CT scans

Question 11

What is an ultrasound scan?

Answer 11

• Abdominal US scans are used to examine the gallbladder, bile ducts, liver, pancreas, spleen, kidneys and large blood vessels. Structures that contain air (such as the stomach and bowels) can’t be examined easily by ultrasound because air prevents the transfer of the sound waves.
• Doppler ultrasound, is used to detect speed and direction of blood flow in certain regions of the body, for example, neck arteries and leg veins.

Question 12

What is a VQ scan ( Ventilation Perfusion)?

Answer 12

• Nuclear med scan that uses radioactive material to examine the airflow (v) and blood flow (p) in the lungs
• Aims to look for evidence of any pulmonary embolism in the lungs, that might be fatal if left untreated
• Carried out in tow parts :
  1.) Radioactive material is breathed in via a nebuliser, pics are taken to look at airflow in the lungs by gamma camera
  2) Diff radioactive material is injected into an arm vein, and more images are taken to see the blood flow in the lungs

Question 13

What is a PET scan?

Answer 13

• positron emission tomography - nuclear imaging test- can reveal metabollic / biochem functions of the tissues and organs
• It uses a radioactive drug tracer to show both typical and atypical metabolic activities of the body
• effective way to help discover a variety of conditions, including cancer, heat diseases and brain disorders. Cancer cells - show uo as bright spots on PET scans (HIGHER metabolic rate than normal cells)
• can reveal areas of decreased blood flow in the heart and help in early diagnosis
• PET scans are also used to check certain brain disorders e.g. tumours. Alzheimer’s

Question 14

What is a SPECT scan?

Answer 14

Single Photon Emission Computerized Tomography
- produces images that show how well blood if flowing in the heart and brain ; areas which are active or which bones are affected by cancer
- Helps diagnose certain vascular brain disorders, treat seizure disorders (epilepsy etc) by pinpointing exact areas of seizure activity in the brain
- Areas of bone healing/ bone cancer progression usually light up on SPECT scans

SPECT can check for narrowed cardiac arteries, damaged myocardium, and can detect reduced pumping efficiency of the heart chambers.

Question 14

What is endoscopy?

Answer 14

• Medical procedure that uses an endoscope to examine the interior of a hollow organ or body cavity by introducing endoscopes directly into the organs

Esophagogastroduodenoscopy - inspects stomach and duodenum
Enteroscopy - small intestine
Colonoscopy - large intestine
cholecystostopy- gall bladder
Cholangiopancreatography (ERCP) - Endoscopic retrograde
Proctoscopy or sigmoidoscopy - rectum or sigmoid colon

Question 15

What are some other types of endoscopy?

Answer 15

Respiratory tract: To inspect nose (rhinoscopy), URT (laryngoscopy), LRT (bronchoscopy), ear (otoscopy).

To visualise urinary tract: Urinary bladder (cystoscopy).

To inspect the female reproductive system: Cervix and vagina (colposcopy), uterus (hysteroscopy), etc.

Closed body cavities can be inspected and treated via endoscopy by making small skin incisions, e.g., to look in abdominal, peritoneal, pelvic cavity (laparoscopy), inspection of the interior of a joint (arthroscopy), to look at organs of chest (thoracoscopy or mediastinoscopy).

Endoscopic procedures are often used in Orthopedic surgeries like hand & knee surgeries, removing bursae (bursectomy), endoscopic spinal surgeries, etc.

Question 15

What is a pleural effusion?

Answer 15

• A collection of fluid in the pleural cavity, caused by many pathological conditions , which overwhelm the pleura’s ability to reabsorb the fluid that gathers in the lowest part of the chest
• CXR findings : if patient is upright when the Xray is taken, fluid will surround the lung base forming a meniscus - obscures costophrenic angle, increased, heart borders and hemidiaphragm
  not seen in supine patient
• Loss of costophrenic angle , increased density of hemithorax, pseudo-elevation of diaphragm, loss of lower lobe vessels seen
• Chest CT findings : Large pleural effusion appears as a sickle -shaped opacity in most dependent part of the thorax , with lateral upward sloping of meniscus-shaped contour. Diaphragmatic contour is partially/ completely obliterated, depending on the amount of fluid

Question 16

How do we detect emphysema in clinical imaging?

Answer 16

Emphysema- abnormal permanent enlargement of airspaces distal to terminal bronchioles accompanied by destruction of the alveolar wall
- BEST evaluated on CT
- CXR findings - hyperinflated lungs with low flattened hemidiaphragm, increased radiolucency of lungs, retrosternal airspace, AP chest diameter , vertical heart, widely spaced tibs, sternal bowing and blunting of costophrenic angles
CT scan finding : Appearance of dark or low attenuation areas, overinflation/ damage of air sacs
- Centrilobular emphysema shows up as small, round dark areas within the central part of the lung lobules
Pan lobular shows uniformly distributed areas of low attenuation throughout lungs

Question 17

How is pneumothorax detected in clinical imaging?

Answer 17

Pneumothorax - presence of air between parietal and visceral pleurae, caused commonly by trauma or injury or spontaneous.
Chest radiographic findings : Visible visceral pleural edge seen as very thin, sharp white line. No lung markings are seen peripheral to this line. Peripheral space is radiolucent compared to adjacent lung. Lung may collapse. Mediastinum shift usually seen in tension pneumothorax
Chest CT findings : Rims of gas (black) seen around edges of the lung which may rack up the fissures. Small pneumothoraces, pneumomediastinum, and blebs can be detected on chest CT.