Perfusion Lung Imaging

Question 1

What is the purpose of lung perfusion imaging?

Answer 1

To provide information of regional blood flow

Question 2

What are the indications of perfusion imaging?

Answer 2

-Pulmonary embolism
-Lung cancer
-Quantification

Question 3

What are some limitations on lung perfusion studies?

Answer 3

-Non specific
-Vent and CXR increase the specificity for PE diagnosis

Question 4

Describe the characteristics of Tc-99m MAA

Answer 4

Mechanism of localization: Capillary blockage
Properties:
-10-90 um diameter
- <5 um localizes in liver
- theres anywhere from 100k to 600k particles
Dose: 45-150 MBq
Biological T1/2: 4-6hrs
-breakdown in lungs due to respiratory motion, enzymes, and blood pressure forces
-Clearance by RES

Question 5

What are reasons for dose adjustments of MAA?

Answer 5

-Pneumonectomy
-R-L shunts
-Pulmonary hypertension
-Pregnancy
-Pediatrics

Question 6

Why calculate MAA particle number?

Answer 6

-Need to ensure a dose of 185 MBq is drawn at any point in the day (6hr expiry)
-has the appropriate particle number
-500k particles in a 185 MBq dose

Question 7

What affects the clearance of MAA?

Answer 7

-Particle size
-Particle number
-Particle hardness
-Lung health

Question 8

Patient Positioning

Answer 8

Injection: Supine, counteracts gravitational and hydrostatic forces
During imaging: same positioning for both vent and perf
If supine: Shoulder downward, ant and post, small pillow, avoid patient from being too elevated

Question 9

What is the injection technique for MAA?

Answer 9

-Minimum 23 gauge needle or larger
-Gently invert syringe before injection
-Avoid withdrawing blood back into syringe (hot emboli)
-Several deep breaths during injection to aerate to maximum alveoli level
-Inject slowly over several respiratory cycles
-Patient supine

Question 10

Describe the views acquired in Perfusion planar

Answer 10

-6-8 standard views
-Ant, post, RPO, LPO, RAO, LAO, LLat, RLat
- 600-800k

Question 11

SPECT imaging

Answer 11

Perfusion: 10 secs per stop, 6 degree angle, 360 degrees
Ventilation: 20 secs per stop, 6 degree angle, 360 degrees

Question 12

What are V/Q imaging techniques?

Answer 12

Perfusion then ventilation:
-Aerosol/vent 3-5 times more than perfusion dose
-Normal perfusion; ventilation unnecessary
Ventilation then perfusion:
-Most common
-Perfusion 3-5 times aerosol dose delivered to lungs

Question 13

Describe PIOPED II criteria of PE

Answer 13

Large: 75% of a lung segment
Medium: 25-75% of lung segment
Small: <25% of lung segment

Question 14

Normal scan critera

Answer 14

No perfusion defects

Question 15

Low probability scan criteria

Answer 15

Small sub-segmental defects

Question 16

Intermediate probability criteria

Answer 16

Moderate segmental defects

Question 17

High probability criteria

Answer 17

2 or more large mismatched segmental defects

Question 18

What is abnormal perfusion interpretation??

Answer 18

-Decreased activity is abnormal
-Defects
-Each area of defect compared with vent image, matched or mismatched

Question 19

Describe what a PE would look like in vent vs. perf

Answer 19

-Wedge shaped mismatched defects
-extends to periphery
-conforms to segmental anatomy
-visible on more than one view (typically)

Question 20

What is the triple match defect?

Answer 20

-Matched V/Q lesion
-Within brachiopulmonary segments
-Occurs in area of a similarly sized radiographic abnormality

Question 21

When would a CTPA be done?

Answer 21

-Abnormal CXR
-Respiratory disease
-critical care patients
-suspected large PE
-acute

Question 22

When would a V/Q be done?

Answer 22

-Normal CXR
-Patient otherwise healthy
-CTPA contraindicated
-Contrast allergy, impaired renal function and high creatinine
-Young patients
-Pregnant patients
-Chronic