Imaging of the lung and mediastinum Flashcards
What can be discerned when imaging the lung fields
Lung fields Diaphragm and recesses Fissures Hilar region Thoracic cage
What can be discerned when imaging the mediastinum
Heart &
Great vessels
Trachea
Soft tissues
Describe medical imaging modalities
Radiography (plain and special)
Computerised Axial Tomography (CT or CAT)
Magnetic Resonance Imaging (MRI)
Ultrasonography (Ultrasound)
Nuclear Medicine Imaging (Radionuclide Imaging) Eg:Technetium-99 scans
Describe PA X-ray
Film is viewed as if you are facing the patient face to face
X-Ray goes through back of patient- X-ray film on chest
X-ray tube
(posterior)
Person/part
Film
(anterior)
Describe the basic projections of the different X-rays
Postero-anterior (PA) view (erect)
Antero-posterior (AP) view (erect or supine )
Lateral view
Describe the PA view of the chest radiograph
Routinely used
Heart close to film
Heart undistorted
Scapula rotated away from lung
Clavicles cross lung fields
Describe the AP view of the chest radiograph
mainly for supine patients
Heart magnified
Scapula overlaps
Clavicles projected above apex
What should you do when you get a chest X-ray
Patient details
Rotation – is the image ‘straight’?
Inspiration – at least top 9 pairs of ribs
Position- AP, PA, lateral, supine, decubitus
Exposure – should be able to see IV discs behind cardiac shadow.
What should you look at on the chest X-Ray
A. Airways B. Bones C. Circulation – heart & vessels D. Diaphragm E. Effusion – lung edges F. Fields – lung fields G. Gas bubble – stomach H. Any others
What should be seen on a chest X-Ray
Lung fields
Mediastinal shadow
Cardiac silhouette
Transverse diameter of heart should not exceed 50% of that of thorax
What is a bronchogram
Radio opaque contrast medium was introduced into the airways to coat the interior surface.
Not used anymore. CT scan reconstructions are available now
What can be seen on a bronchogram
RUL-right upper lobe bronchus
RML- right middle lobe bronchus
RLL- right lower lobe bronchus
A -Trachea
B- Left main bronchus
C- Left upper lobe bronchus
D- Left lower lobe bronchus
Describe a pneumothorax
Right lung collapsed
Hence no vascular markings
Hyperlucent right lung field
Air in pleural cavity
Clavicle fracture No lung markings on right side No lung sounds –right side Tachycardia + Treatment -Chest drain placed
Describe pleural effusion
Fluid in right middle lobe fissure
Fluid level in relation to the right dome
Right costo-diaphragmatic recess obliterated
Describe lung- hilar lymphadenopathy (lung enlargement)
Lymph node masses usually due to sarcoid or lymphoma e.g carcinoma of uterine cervix.
Describe pulmonary artery angiogram
Radio opaque contrast material is injected into the pulmonary artery and imaged as it passes through the arterial tree.
Arteries (blue lines) are more vertical than veins
Describe the pulmonary vein angiogram
Radio opaque contrast material is injected into the pulmonary artery and imaged as it passes through the venous tree.
Veins (red lines) are more horizontal than arteries
Which chest view is used to image the heart
PA view is routinely used to evaluate the heart
Heart is close to film
Heart undistorted
What impressions can be seen on the oesophagus
Aortic arch
Lt main bronchus impression
Left atrial impression
What are the cardiac outlines
Aortic arch Pulmonary artery Appendage of LA LV RA SVC Cardiophrenic angle (angle between heart and diaphragm)
Describe subtraction angiography
During angiography it is often difficult to appreciate the contrast agent in the vessels through the overlying bony structures.
To circumvent this, the technique of subtraction of angiography has been developed.
One or two images are obtained before the injection, the images are inverted (negative image created from a positive one)
After injection- series of images obtained to determine passage of contrast agent
By adding the negative precontrast agent to the positive postcontrast, the bones and soft tissue are subtracted to produce a solitary image of contrast only.
How are images obtained in a CT scan
X-ray tube moves in an arc around the body
The image detectors moves in opposite direction in the same arc
Only the axial point is in focus
The signals are put into a computer
The image is reconstructed by the computer and displayed
Describe the planes of the images in CT
Images in axial (transverse) sections (with some exceptions)
Images viewed from inferior side (normal convention)
X-rays are used for imaging
Good details and relations
Choices: Standard CT, CT angiography, Contrast, Windowing, and Reconstructions
What is meant by a window setting
After a CT scan is obtained the data is digitally manipulated to reveal different structures in great detail
Describe MRI
MR imaging is similar to CT but more details and tissue differentiation is seen.
MRI uses strong magnetic field
Depends on the alignment of protons of hydrogen atoms (of water in body tissues) in the magnetic field
Radio waves are used to excite these protons which then ‘flip over’
Flipped protons give measurable energy (signal) when they flip back when the pulsing is removed
More protons (tissues with high water content) emit larger signal
Signals are processed by a computer and images are formed
What is an advantage of MRI
However, an advantage of MRI is the ability to image in any plane – with the obliquity of the heart, this enables us to visualise areas of more relevance through cardiac-specific planes.
What are the different uses of T1 and T2 MRIs
Image c is T1 weighted to show soft tissue structures more clearly
Image d is T2 weighted to show fluid filled areas more clearly
