1. Basics of Medical Imaging

Question 1

What are the types of clinical imaging?

Answer 1

• transmission imaging
• reflection imaging
• emission imaging

Question 2

What are the transmission imaging modalities?

Answer 2

• X-ray modalities: radiographs, mammography, fluorosopy, CT
• a beam of high energy photons is passed through the body and they are either attenuated or blocked

Question 3

What are the reflection imaging modalities?

Answer 3

• reflection of sound waves by the tissues
• ultrasonography (w/ doppler function), sonoelastography

Question 4

What are the emission imaging modalities?

Answer 4

• nuclear medicine: gamma/positron emission from radioisotopes
• MRI: radiofrequency signal emission from hydrogen atoms

Question 5

What is spatial resolution?

Answer 5

• it is the measure of the ability to differentiate objects from one another on imaging, when objects are in close proximity (measured in line pairs per mm, lp/mm)
• CT spatial resolution can be enhance by HRCT
• spatial resolution of nuclear medicine in relatively poor
• submillimeter-sized microcalicifications can be detected by excellent spatial resolution on radiographs

Question 6

What is contrast resolution?

Answer 6

• ability to differentiate between different intensities on an image
• radiography differentiates 5 principle densities: metal, bone, water, fat and air
• MR has excellent soft tissue resolution
• contrast agents are used to enhance the contrast resolution

Question 7

What are contrast agents?

Answer 7

• a substance used to increase contrast resolution in medical imaging
• different forms of contrast agents that can also be administered differently according to the substance
• each modality has contrast agents specific to it

Question 8

What is the terminology for describing a radiograph?

Answer 8

• darker structures have low attenuation and more lucency – increased transparency or radiolucent
• brighter structures have high attenuation and more opacity – decreased transparency or radiopaque

Question 8

What is the terminology for describing CT images?

Answer 8

• hypodense: dark structures with low attenuation
• moderate density
• hyperdense: brighter structures with high attenuation

Question 9

What is the terminology used to describe US images?

Answer 9

• anechoic: appears black
• hypoechoic: appears dark
• hyperechoic: appears bright
• echodense: appears white

Question 10

What is terminology used to describe MR images?

Answer 10

• hypointense: low signal intensity, appears darker
• intermediate signal intensity
• hyperintense: high signal intensity, appears bright

Question 11

What is the terminology used to describe nuclear medicine images?

Answer 11

• low radiopharmacon uptake: appears dark
• high radiopharmacon uptake: appears brighter

Question 12

What are the types of ionizing radiation?

Answer 12

• X-rays
• mammography
• fluoroscopy
• computed tomography
• nuclear medicine

Question 13

What are the types of non-ionizing radiation?

Answer 13

• ultrasonography
• magnetic resonance imaging

Question 14

What are the hazards of ionizing radiation?

Answer 14

• EM emissions with sufficient energy can result in the formation of free radicals in the body, which are highly reactive
• annual radiation dose from natural sources is 2.5 mSv/year
• ALARA principle is important to minimize hazards

Question 15

What to consider in choosing the most ideal modality?

Answer 15

• spatial resolution
• contrast resolution
• depth of penetration
• artefacts
• speed of acquisition
• summation
• ionizing radiation
• contraindications
• cost
• availability

Question 16

What are the major strengths of radiography?

Answer 16

• fast
• available
• great spatial resolution

Question 17

What are the major strengths of fluoroscopy (and DSA)?

Answer 17

• functional information
• real-time imaging
• therapeutic intervention

Question 18

What are the major strengths of CT?

Answer 18

• fast
• 3D imaging
• available
• multiple regions can be examined in short time

Question 19

What are the major strengths of US?

Answer 19

• no ionizing radiation
• available (point-of-care)
• cheap
• real-time imaging
• no contraindications
• contrast enhanced US

Question 20

What are the major strengths of MRI?

Answer 20

• no ionizing radiation
• 3D
• great contrast resolution
• angiography w/o contrast

Question 21

What are the major strengths of nuclear medicine?

Answer 21

• functional information
• early detection

Question 22

What is the patient preparation for interventional radiology procedures?

Answer 22

• INR and platelets testing (in moderate/high risk procedures)
• minimum 4 hour fasting before procedure

Question 23

What is the patient preparation for US?

Answer 23

• minimum 6 hour fasting for abdominal US
• moderately full urinary bladder for pelvic US
• no special preparation for contrast enhanced US

Question 24

What is the patient preparation for US?

Answer 24

• removal of metallic objects, or any electronic device
• exclusion of aneurysm clip
• pacemaker testing and reprogramming
• gadolinium administration should be used with caution if GFR<30
• at least 7 days between injection of contrast agents for patients with GFR<30
• testing for renal function is not mandatory
• moderately full bladder for pelvic MRI
• exclusion of pregnancy before gadolinium administration
• fasting is not recommended before administration of gadolinium