Plain radiographic film
Metal filament in X-ray tube heated causing emission of electrons. Electrons are accelerated and focused onto a metal target. Collision of electrons with nuclei of metallic atoms causes emission of X-rays. X-rays pass through body and hit X-ray plate detector which goes black. The more X-rays that hit the detector, the more black the target gets. Higher-density tissue absorbs and deflects more X-rays so less X-rays reach detector. Six main densities seen on X-ray image: air (black), fat, soft tissue, fluid, bone, and metal (white).
• Chest: useful in primary workup to assess heart and lungs. Also useful in follow-up to monitor progression of disease and/or resolution.
• Abdomen: limited use with the availability of CT but still used to look for bowel obstruction or perforation or to see radio-opaque kidney stones.
• ED trauma: used following trauma (trauma series including cervical spine, chest, pelvis, likely fracture sites) to identify fractures and in follow-up to assess response to treatment/complications.
• Orthopaedics: used to assess joint destruction to decide on management or to follow-up joint replacements or metalwork placement. Also used for follow-up on conservative and operative management (e.g. non-union, malunion, etc.).
• Rheumatology: used to assess arthritic distribution, changes over time, and response to treatment.
• Mammography: exclusive breast X-rays to look for soft tissue lumps and calcifications as part of the national screening programme for breast cancer.
Current passed through piezoelectric crystal causes it to resonate and produce sound waves. Sound waves pass through body and reflect off different density interfaces.
Echoes are detected by crystal which allows formation of image showing interfaces. Sound waves pass easily through fluid due to low echogenicity and appear black on image. Sound waves cannot pass through air or bone due to high echogenicity and reflect off showing no image beyond.
• Liver: focal lesions, cirrhosis, biliary duct dilatation, portal or hepatic vein occlusion.
• Spleen: focal lesions, infarcts, haemorrhage.
• Pancreas: tumours, cysts, pancreatitis.
• Gallbladder: gallstones, cholecystitis, cholangiocarcinoma.
• Bowel: can also see and assess free fluid. Often bowel can be seen (if fluid filled) however, air-filled bowel will obscure underling structures as US unable to pass through air.
• Kidneys: stones, hydronephrosis, renal artery/vein occlusion. (See Fig. 44.1.)
• Bladder: tumours, calcification, stones.
• Uterus: endometrium, fibroids.
• Ovaries: cysts, torsion.
• Prostate: size, focal lesions including transvaginal or transrectal US.
Can be used to assess size of pleural effusion and to characterize the fluid contents including the presence of septations ± loculations (can be hard to detect on CT). Drains can be inserted under US guidance.
Can give excellent views of lumps which are not seen on mammography or find lesions to biopsy. Also used to assess or biopsy axillary lymph nodes.
Excellent views looking for focal lesions, microlithiasis, torsion, hydroceles, or varicoceles.
Almost any vessel can be imaged including arteries (carotids to assess in patients at risk of TIA, aorta looking for AAA, iliacs, femorals, arm and leg arteries looking for atherosclerotic disease) and veins (jugulars and subclavians to assess for central line placements, arm and leg veins looking for DVT or thrombophlebitis).
Most peripheral joints can be imaged to assess the tendons, bursae, and capsules having the benefit of dynamic imaging unlike CT and MRI.
Used in neonates with patent fontanelles to give intracranial views in preference to CT due to ionizing radiation.
Uses X-rays to build up an internal view of the body and can formulate 3D models of patients. Any part of the body can be imaged.
X-rays pass through body from 360° around patient. Depending on different absorptions of intervening tissues, different amounts will pass through to other side, which are detected. By adding all the different images from 360° a 3D image is formed of all internal structures. Each pixel is given a number (Hounsfield unit (HU)) which denotes its density or attenuation. Each tissue type has a particular HU which aids in differentiating pathology. Contrast agents can be given via various routes and at different stages in the scan process to help improve image quality. Oral or rectal contrast can be given to help identify a leak in the GI tract or to simply opacify the bowel so it is easier to differentiate it from the other structures. Contrast can also be injected into the bladder for similar reasons.
IV contrast can be given to help identify various structures (see Fig. 44.2). The length of time following administration and image acquisition will determine what type of scan is performed:
• At 15–25 sec the contrast will be in the pulmonary arteries, as in CTPA to diagnose PE.
• At 30–40 sec the main systemic arteries will opacify which would help to look for aneurysms or acute bleeding.
• At 70–90 sec the abdominal organs will begin to take up contrast and this helps to identify focal lesions or delayed bleeding.
• After 2–3 min the contrast would start to be excreted by the kidneys and therefore the ureters and bladder would begin to fill with contrast helping to identify obstruction or tumours in the renal tract.
Magnetic resonance imaging
MRI uses magnets and radiofrequency pulses to build up an internal view of the body. It is particularly useful for soft tissue characterization and musculoskeletal imaging to view tendons and ligaments which cannot be identified on CT. This modality is also useful for identifying different tissue types within lesions. Any part of the body can be imaged (see Fig. 44.3).
Hydrogen nuclei are aligned in a strong magnetic field. Radiofrequency pulses cause hydrogen nuclei to flip by varying degrees.
Nuclei spin back to their original alignment and give out varying signals dependent on what type of tissue they are located in. A computer detects signals returned from nuclei and displays them as an image. Different sequences can be performed by altering degrees of spin and by repeating radiofrequency pulses which help differentiate different tissue types.
Real-time sequential X-ray pictures can be acquired of any region of the body
Contrast studies: administration of contrast via any cavity in the body and fluoroscopy performed to monitor the passage of that contrast through the body.
Oral or rectal administration of contrast enables opacification of the GI tract to demonstrate luminal pathology such as polyps, strictures, diverticula, or tumours (see Fig. 44.4).
Injection of contrast via a catheter into the uterus is used to opacify the uterus and fallopian tubes to identify patency in patients with subfertility (see Fig. 44.5).
Injection of contrast into a nephrostomy or urinary bladder catheter or opacify the renal tract or identify a bladder leak or urethral injury.
Injection of contrast into any drain, line, or indwelling tube to ascertain its position and/or patency such as blocked venous lines or abdominal drains.
Radio-labelled pharmaceuticals are injected into patients which migrate to various tissues and emit gamma rays. These are then picked up by a gamma camera and show where the pharmaceutical has migrated to. This enables physiological activity within various cells in the body to be determined. There are numerous pharmaceutical agents which can be radiolabelled depending on where you want the tracer to be absorbed such as thyroid, kidney, bone (Fig. 44.6), heart, lung, white cells, etc.
PET-CT: this is a fusion of PET (a cross-sectional version of nuclear imaging) and CT to produce images with anatomical data from CT with overlayed physiological data from PET. This shows the exact sites of physiological activity such as small metastatic deposits.
This is a vastly expanding subspeciality field of radiology. Procedures range from simple US-guided biopsies to fluoroscopy-guided complex EVARs. Interventional radiology is divided into two further fields of vascular and non-vascular. Common procedures can be divided into vascular and non-vascular cases which include:
Vascular interventional radiology
• Angioplasty/venoplasty and stenting of atherosclerotic or aneurysmal vessels.
• Endovenous laser treatment of varicose veins.
• Thrombolysis for acute clot and emergency embolization in acute haemorrhage, including postpartum haemorrhage.
• Inferior vena cava filter placement and retrieval.
• Embolization of arteriovenous malformations.
• Tunnelled central line insertion.
• Transjugular intrahepatic portosystemic shunt (TIPS) for portal hypertension.