Alternative Imaging Modalities Flashcards
(72 cards)
1
Q
What are 2 other terms for computed tomography?
A
- Conventional CT
- CAT scan (historical).
2
Q
What is CT?
A
- Form of CROSS SECTIONAL imaging which allows SOFT TISSUE and BONY ANATOMY to be visualized well.
3
Q
What can be used to help visualize the soft tissues in patients undergoing CT?
A
- IODINATED CONTRAST intra-venously to increase soft tissue contrast.
4
Q
What makes up a CT image?
A
Voxels.
5
Q
What is the shape of the beam for CT and CBCT?
A
- CT: fan shaped.
- CBCT: cone shaped.
6
Q
Does CT or CBCT have a higher radiation dose?
A
CT has a HIGHER RADIATION DOSE.
7
Q
Is CT or CBCT good at visualizing soft tissues?
A
- CT: Good soft tissue contrast (windowing).
- CBCT: poor soft tissue contrast.
8
Q
What is the patient positioning for CT and CBCT?
A
- CBCT: patient upright/ standing.
- CT: patient lying horizontal.
9
Q
When is radiographic contrast used?
A
- CBCT: not required as not looking at soft tissues.
- CT: can be used if indicated.
10
Q
2 disadvantages of CT and CBCT?
A
- Metallic artefacts from dental restorations, surgical plates, jewellery etc.
- Expensive compared to plain radiography.
11
Q
What is meant by isotropic voxel?
A
Same in dimensions in height, breadth and width.
12
Q
What are voxels?
A
3D pixels.
13
Q
What makes up the image of CT? of CBCT?
A
Both made of VOXELS.
14
Q
What is the benefit of isotropic voxels?
A
Allow manipulation of images in ALL THREE PLANES (axial, coronal and sagittal) with NO DISTORTION.
15
Q
What is the difference between CT and CBCT voxels?
A
CT voxels are gives a value of DENSITY - HOUNSFIELD UNITS.
16
Q
What are hounsfield units?
A
Values of DENSITY given to CT VOXELS.
17
Q
What are the hounsfield numbers for air, fat, water and dense bone?
A
- Air: -1000.
- Fat: -100 to -60.
- Water: 0.
- Dense bone: +1000.
- the lower the number, the closer to BLACK. The higher the number, the closer to WHITE.
18
Q
What is the hounsfield number of metal restorations?
A
Higher than dense bone (1000) hence will appear DARKER.
19
Q
What is windowing?
A
Alters the levels of DENSITIES visualized in scan to optimally look at SPECIFIC TISSUES.
20
Q
Define window level
A
value at centre of range
21
Q
Define window width
A
range of values selected to view tissues
22
Q
What is the effective dose (mSv) for single bitewing, teeth (panoramic), CT head, CT chest, CT abdomen/pelvis?
A
- Single bitewing: <0.01
- Teeth (panoramic): 0.01
- CT head: 2
- CT chest: 8
- CT abdomen/pelvis: 10
23
Q
What is the equivalent says of background natural radiation for single bitewing, teeth (panoramic), CT head, CT chest, CT abdomen/pelvis?
A
- Single bitewing: <1.5 days
- Teeth (panoramic): 1.5 days
- CT head: 1 year
- CT chest: 3.6 years
- CT abdomen/pelvis: 4.5 years
24
Q
Where is the magnetic field for MRI located?
A
The entire room is magnetic field.
25
How do we gain higher detail over the area of interest on MRI?
IMAGING COIL placed over region of interest to gain higher resolution.
26
What 3 things are used to produce images in MRI?
1. Magnetic field.
2. Radiofrequency pulses
3. Hydrogen protons (within water molecules within the body).
27
Why do tissues in the body (ex. bone, fat) appear differently on MRI?
Every tissue in the body has a DIFFERENT LEVEL OF WATER CONTENT and will thus produce a DIFFERENT SIGNAL which corresponds to DIFFERENT DENSITY.
28
What is the "physics/ chemistry" behind the acquisition of an MRI image?
Once patient lies in the MRI unit, a MAGNETIC FIELD is applied which starts to OSCILATE THE PROTONS.
When the magnetic field is removed, the protons RELAX TO NORMAL POSITION, and EMIT RADIOWAVES which are picked up by detectors.
29
What color does cortical bone appear as on MRI?
Cortical bone is always BLACK.
30
What are T1 and T2 MRi sequences best for?
- T1: good for anatomy, fat appears WHITE.
- T2: good for pathology, fat and fluid appear WHITE.
31
You want to visualize pathology. Which MRI sequence would you choose?
T2 - good for pathology, FAT and FLUID appear WHITE.
32
You want to visualize anatomy. Which MRI sequence would you choose?
T1 - good for anatomy, FAT appears WHITE.
33
What contrast can be used in MRI?
GADOLINIUM - can help highlights areas of pathology, ex. cancer.
34
2 advantages of MRI?
- No ionizing radiation.
- Very good imaging of soft tissues + early changes in bone marrow.
35
2 disadvantages of MRI?
- Multiple contraindications.
- Lengthy scans (15 mins to 1 hour).
- Claustrophobia.
- Cost + availability (more time consuming thus less people are scanned daily).
36
5 contraindications to MRI
Pacemakers, Orbital foreign bodies, artificial heart valves, joint replacements, surgical clips.
37
Why must we avoid magnetic metal in MRIs?
Any metal within the body has a chance of being magnetic, thus will be ATTRACTED TO THE UNIT, will MOVE THROUGH TISSUES and cause PAIN/ BE FATAL.
38
Are dental implants safe for MRI?
Yes.
39
How would the articular disc present on a sagittal view MRI?
Dark gray, bow tied shaped mass.
40
Where does the articular disc sit normally?
Between the articular eminence and condylar head.
41
3 structures that we can visualize using MRI?
- TMJ (can see condylar bone and articular disc).
- Salivary glands
- Perineural spread of malignancy.
42
What is used to produce the images in ultrasound?
High frequency sound waves.
43
What is the procedure for an ultrasound? (how is it acquired).
- TRANSDUCER is placed on SKIN surface with a COUPLING AGENT (gel) between the probe and skin to allow SOUNDWAVES TO PENETRATE.
44
What structures is ultrasound good for?
- Good for SUPERFICIAL structures.
- Sound waves CANNOT penetrate dense bone (anything behind bone will not be seen).
45
What creates the depth of images on ultrasound?
- As sound waves hit tissue boundaries, they REFLECT back to the probe.
- The **LENGTH OF TIME** it takes for sound waves to return will create level of depth to images.
46
5 advantages of ultrasound?
- No ionizing radiation.
- Good for superficial structures.
- Real time imaging.
- Can be used as adjunct to biopsy/aspirates.
- Blood flow.
47
4 disadvantages to ultrasound?
- Operator dependent.
- Can't penetrate bone.
- Only superficial structures are seen.
- Can be difficult to interpret.
48
What specific OROFACIAL structure may ultrasound not be ideal for imaging and why?
**PAROTID GLAND**
- Parotid wraps around MEDIALLY, deep to the ramus of the mandible. This will NOT be seen on ultrasound - IMPORTANT IF CONSIDERING A NEOPLASTIC MASS.
49
What imaging modality can be used to assess for salivary gland sjogrens, neoplasia, sialadenitis or sialoliths?
MRI
50
4 examples of use of ultrasound in HEAD AND NECK?
1. **Neck lumps** (cysts, tumots, lymph nodes).
2. **Salivary glands** (Sjogrens, neoplasia, sialadenitis, sialoliths).
3. **Guidance for biopsy.**
4. **Vascular** (carotid artery stenosis, AVM, hemangioma).
51
What will be seen on ultrasound of the submandibular gland of normal vs Sjogren's syndrome?
- **Normal**: Well defined submandibular gland with homogenous density to the parenchyma.
- **Sjogren's**: No clearly defined periphery of submandibular gland. Heterogenous density to the parenchyma.
52
- Well defined, ovoid, heterogenous mass.
- Has POSTERIOR ENHACEMENT (brighter area behind the mass).
53
What must we ensure about ranulas?
Must ensure it does not herniate into the SUBMANDIBULAR space, making it a PLUNGING RANULA.
54
3 examples of nuclear medicine?
- PET (positron emission tomography).
- SPECT (single photon emission CT).
- Scintigraphy (uses gamma camera).
55
How is am image obtained using nuclear medicine?
Patient is typically INJECTED INTRA-VENOUSLY with a RADIOPHARMACEUTICAL which when it decays (via half life) emits particles that are picked up on gamma camera.
56
What is increased activity picked up as on nuclear medicine scans?
Hot spot
57
What is reduced activity picked up as on nuclear medicine scans?
Cold spot
58
3 advantages of NM scans?
1. can be superimposed over other cross-sectional imaging (ex. conventional CT).
2. Highly sensitive.
3. Can assess function (ex. salivary glands, thyroid).
59
What kind of scan can be used to assess function of salivary glands?
NM scan.
60
3 disadvantages of NM scans?
1. Poor resolution.
2. Poor specificity (can be malignancy, inflammation, infection or false positive).
3. Very high radiation dose.
61
How can we help minimize the effect of poor specificity of NM scans?
Important to relate the findings of a NM scan with conventional anatomical imaging (plain film or cross-sectional).
62
Two common radioisotopes used in nuclear medicine?
- Technetium -99M.
- 18-FDG.
63
What is the half life of technetium 99M? what is its advantage?
- Short half life (6 hours).
- Can be bound to different substances that are taken up by specific tissues.
64
What type of technetium 99M can be used to visualize bone?
MDP (methylene diphosphonate).
65
What type of technetium 99M can be used to visualize thyroid and salivary glands?
Pertechnetate.
66
What does 18-FDG stand for?
Fluorine labelled glucose.
67
What is the half life of 18-FDG
Just under 2 hours.
67
What is 18-FDG usually taken up by? Why is it typically used (2)?
Taken up by metabolically active tissues as the glucose is needed for increased levels of mitosis. Typically used for PET scans for looking for:
1. Distant metastases.
2. Unknown primary cancer from diagnosed metastatic neck lump.
68
What type of nuclear medicine scan is most often superimposed over conventional CT?
Pet (positron emission tomography).
69
What are the benefits of superimposing PET scan with conventional CT?
- PET scan uses 18-FDG and hives high sensitivity for INCREASED GLUCOSE UPTAKE.
- CT gives high resolution for anatomical detail.
70
What is a PET-CT typically used for?
1. CANCER DIAGNOSIS - Unknown primary disease (patient presents with solitary neck lump and nothing on clinical exam).
2. ASSESS RECURRENCE.
3. ASSESS HOW EFFECTIVE TREATMENT HAS BEEN.
4. DISTINGUISH BETWEEN ACTIVE DISEASE VS SCAR TISSUE.
71
What does SPECT stand for? What can be its use in dentristry?
- Single photon emission computed tomography.
- Used to diagnose CONDYLAR HYPERPLASIA (condyle still growing will appear as a hot spot).
