Modality key concepts

Question 1

What is the effect of a thin slice in CT imaging?

Answer 1

More images, more detail, but also more noise.

Question 2

What is the axial view in CT imaging?

Answer 2

As if looking from patient’s feet to their head. Moves up and down (superior/inferior) through the body.

Question 3

What is the coronal view in CT imaging?

Answer 3

As if looking at the patient face to face. Moves forwards and backwards (anterior/posterior) through the body.

Question 4

What is the sagittal view in CT imaging?

Answer 4

As if looking at the patient side-on. Moves side-to-side (left/right) through the body.

Question 5

How are shades of grey represented in CT imaging?

Answer 5

Based on (radio)density (measured in Hounsfield units).

Question 6

What do bone and contrast agents appear as in CT imaging?

Answer 6

White/bright (radio-dense).

Question 7

What does air appear as in CT imaging?

Answer 7

Black (radiolucent).

Question 8

How do soft tissues appear in CT imaging?

Answer 8

Various shades of grey.

Question 9

How does fat appear in CT imaging?

Answer 9

Fat is always more radiolucent.

Question 10

What are contrast agents used for in CT?

Answer 10

Radio-dense, used to highlight structures of interest. Heavy metal elements used for contrast.

Question 11

What is the effect of IV contrast administration?

Answer 11

Highlights vasculature initially. Highlights soft tissue differences after a delay.

Question 12

What is the purpose of enteric contrast administration?

Answer 12

Highlights gastrointestinal system. Oral for proximal gut structures. Enema for distal gut structures.

Question 13

What is seen in the early & late arterial phase with IV contrast?

Answer 13

Arteries appear densely white. Organs start to display differing brightness levels. IVC still shows normal fluid density signal.

Question 14

What occurs in the portal venous phase with IV contrast?

Answer 14

Contrast disperses more evenly. Aorta and IVC appear similar in tone. Soft tissues are highlighted in different shades of grey.

Question 15

What is windowing in CT?

Answer 15

Adjusting image settings to highlight different structures of interest.

Question 16

What does window width (WW) select in CT?

Answer 16

Selects range of Hounsfield units displayed. Everything outside the WW appears black or white.

Question 17

What is window level (WL) in CT?

Answer 17

Midpoint of the range, usually set to the tissue of interest.

Question 18

What is soft tissue windowing in CT?

Answer 18

Narrow width. Lung parenchyma appears solid black, bones solid white. Soft tissues contrasted strongly within grey scale.

Question 19

What is lung windowing in CT?

Answer 19

Wider width. Captures lung parenchyma details but washes out soft tissues. Bones remain solid white.

Question 20

What is bone windowing in CT?

Answer 20

Relatively wide window, skewed to the right. Captures fine bone details. Less dense structures (sinus cavities/lungs) appear solid black.

Question 21

What is the effect of high-power magnetic fields in MRI?

Answer 21

Affect protons (water molecules in the body). Magnetic field aligns protons.

Question 22

How is an MRI image formed?

Answer 22

Radio pulses distort alignment and then release them again (relaxation phase). Energy released from relaxation is detected as radiowaves to create an image.

Question 23

What do different MRI pulse sequences create?

Answer 23

Different grey scales (e.g., T1 vs. T2). Very high resolution for soft tissues.

Question 24

How does bone appear in MRI?

Answer 24

Bone Cortex = Always black on MRI (few protons present).

Question 25

What does 'hyperintense' mean in MRI terminology?

Answer 25

'Hyperintense' = Bright areas.

Question 26

What does 'hypointense' mean in MRI terminology?

Answer 26

'Hypointense' = Dark areas. Grey scale may change, but anatomy remains the same.

Question 27

What are MRI contrast agents used for?

Answer 27

Gadolinium can enhance images further.

Question 28

What does T1 imaging indicate?

Answer 28

'Fat is bright.' Subcutaneous fat appears bright. Fluid-filled structures appear dark.

Question 29

What does T2 imaging indicate?

Answer 29

'Water is white.' CSF appears very bright.

Question 30

What are some advantages of a CT scan?

Answer 30

Fast (1-20 minutes), relatively widely available, 3D reformatting and reconstruction, intermediate cost.

Question 31

What are some common uses of a CT scan?

Answer 31

Acute trauma, stroke (to rule out bleed), angiography with contrast media.

Question 32

What is the principle behind how a CT scan works?

Answer 32

The anode is paired with a detector array that rotates 180 degrees to produce a narrow, continuous fan-shaped stream of x-rays, which is then reconstructed into a stack of 2D images using algorithms.

Question 33

How is the technique of a CT scan quantitative?

Answer 33

The technique uses a linear transformation of the original tissue attenuation, and the Hounsfield unit of each voxel is calculated.

Question 34

What is the Hounsfield unit value for water and air in CT scans?

Answer 34

Water = 0, Air = -1000.

Question 35

What can the Hounsfield units in CT scans be used for?

Answer 35

Density quantification, such as identifying calcified vessels.

Question 36

What is a major disadvantage of CT scans?

Answer 36

They use a high dose of ionizing radiation.

Question 37

What is the cost of a CT scan?

Answer 37

It has an intermediate cost.

Question 38

How does bone appear on a CT scan?

Answer 38

Bone appears as high intensity (bright).

Question 39

How does gray matter appear on a CT scan?

Answer 39

Gray matter appears light grey.

Question 40

How does white matter appear on a CT scan?

Answer 40

White matter appears as darker grey.

Question 41

How does cerebrospinal fluid (CSF) appear on a CT scan?

Answer 41

CSF appears hypointense (dark).

Question 42

How does fat appear on a CT scan?

Answer 42

Fat appears very dark/hypointense.

Question 43

How does muscle appear on a CT scan?

Answer 43

Muscle appears as mid grey.

Question 44

How does blood appear on a CT scan?

Answer 44

Blood intensity can range from high to low depending on the stage (e.g., fresh blood is high intensity, older blood is lower intensity).

Question 45

What is intra-vascular contrast media?

Answer 45

Intra-vascular contrast media are compounds injected to increase the contrast of structures or fluids on imaging.

Question 46

Do intra-vascular contrast media cross the blood-brain barrier (BBB)?

Answer 46

Intra-vascular contrast media usually do not cross the blood-brain barrier unless it is not intact.

Question 47

What type of contrast media is used for x-rays (angiography) and CT scans?

Answer 47

Iodinated contrast media are used for x-rays (angiography) and CT scans.

Question 48

What happens in areas of pathology such as tumours or strokes regarding contrast media?

Answer 48

In areas of pathology like tumours or strokes, 'leaky' vessels allow the contrast agent to enter the abnormal tissue and wash out slowly. This results in high signal visualization on scanning.

Question 49

What are the risks of using iodinated and gadolinium-based contrast media in patients with renal failure?

Answer 49

Both iodinated and gadolinium-based contrast media are associated with poor outcomes when used in renal failure, as they are excreted via the kidneys.

Question 50

How can iodinated contrast media affect renal function?

Answer 50

Iodinated contrast media can exacerbate poor renal function.

Question 51

What is the rate of contrast reactions with iodinated media?

Answer 51

The rate of contrast reactions with iodinated media is high.

Question 52

What was previously considered about the safety of gadolinium-based contrast media?

Answer 52

Gadolinium was considered very 'safe' in the past.

Question 53

What rare condition can gadolinium-based contrast media cause in patients with poor renal function?

Answer 53

Gadolinium-based contrast media can cause nephrogenic systemic fibrosis when used in large doses in patients with poor renal function, due to gadolinium deposition in tissues.

Question 54

Where has gadolinium been found to deposit recently?

Answer 54

More recently, gadolinium has been found to deposit in the brain and bones.

Question 55

What are the advantages of MRI?

Answer 55

No ionizing radiation Excellent for brain imaging Versatile with multiple modes/sequence types Good for prenatal brain imaging Contrast can be manipulated Acute ischemia demonstrated early when CT is normal Useful for tumors and angiography (with or without contrast) Multiplanar imaging

Question 56

What are the disadvantages of MRI?

Answer 56

Safety issues (implants with metal, flying metal objects, cochlear implants, joint replacements, tattoos, mascara, cardiac pacemakers, cerebral aneurysm clips, shrapnel) Long acquisition time (10–120 minutes) Poorer access and expensive Motion sensitivity Requires high-level expertise to acquire images Complex examinations lead to substantial post-processing times Artifacts from metals (e.g., joint replacements, tooth fillings)

Question 57

What are the basic principles of MRI?

Answer 57

The body is placed in a powerful magnetic field (30,000+ times Earth's magnetic field) Proton nuclei align themselves with the magnetic field, acting like tiny bar magnets A radiofrequency pulse is applied perpendicular to the main field, flipping the direction of the aligned nuclei

Question 58

What happens after the RF pulse is removed in MRI?

Answer 58

When the RF pulse is removed, the nuclei realign with the main magnetic field. As they do so, they lose energy and emit their own signal. This signal varies with tissue type and pulse sequence, and the energy is processed to create image contrast/information.

Question 59

What are some common MRI sequence types?

Answer 59

T1 T2 FLAIR (Fluid Attenuated Inversion Recovery) Proton density DWI (Diffusion Weighted Imaging) DTI (Diffusion Tensor Imaging) Angiography (with or without contrast media, e.g., Arterial Spin Labeling, Time of Flight) Perfusion imaging Functional MRI (task-dependent and resting state) Spectroscopy

Question 60

How do T1 and T2 sequences differ in MRI?

Answer 60

T1 sequence: CSF is hypointense, fat is hyperintense T2 sequence: CSF is hyperintense, fat is usually hypointense

Question 61

What happens when contrast agents like gadolinium are administered in MRI?

Answer 61

When contrast agents like gadolinium are administered, areas with a compromised Blood-Brain Barrier enhance on T1W imaging.

Question 62

What is the basic principle behind ultrasound imaging?

Answer 62

Ultrasound imaging uses high-frequency sound waves to create images of structures inside the body. The sound waves are emitted by a transducer, which then measures the reflections (echoes) from tissues, helping to form an image.

Question 63

What is the role of the transducer in ultrasound?

Answer 63

The transducer emits sound waves and receives the echoes that bounce back from the body's tissues. It is the primary tool used to capture the data required for creating the ultrasound image.

Question 64

What factors affect the quality of ultrasound images?

Answer 64

The quality of ultrasound images can be influenced by factors such as the frequency of the sound waves, the type of tissue being imaged, the skill of the operator, and the quality of the equipment.

Question 65

What is the difference between high-frequency and low-frequency ultrasound?

Answer 65

High-frequency ultrasound provides higher resolution but less depth, making it useful for imaging superficial structures. Low-frequency ultrasound provides deeper penetration but lower resolution, making it suitable for deeper structures.

Question 66

What is a primary disadvantage of ultrasound in terms of image resolution?

Answer 66

Ultrasound has relatively low resolution compared to other imaging modalities like CT or MRI, which can limit the detail in images of deeper or smaller structures.

Question 67

Why is ultrasound limited in terms of depth?

Answer 67

Ultrasound is limited in depth because sound waves lose energy as they penetrate deeper into the body. This means that ultrasound is generally more effective for imaging superficial tissues but is less effective for deeper structures.

Question 68

How does operator skill affect ultrasound imaging?

Answer 68

Ultrasound imaging is operator dependent, meaning the quality of the images can vary based on the experience and skill of the technician performing the scan. Proper technique is crucial to ensure accurate and high-quality images.