Week 4: Injection Techniques Flashcards
1
Q
Method of injecting iodinated CM will vary according to:
A
- Vascular access available
- Type of examination
- Specific clinical indication
2
Q
Injection parameters may/will vary:
A
If the injection is performed by hand or using a mechanical injector
- Contrast volume and concentration
- Flow rate at which the contrast will be injected
- The delay between injection and scanning
- Whether a saline flush is used
3
Q
CVAD (central venous access device)
A
- a venous catheter designed to deliver medications & fluids directly into SVC, IVC, or right atrium
- several types (PICC, nontunneled, tunneled, implantable)
- not optimal for CM but sometimes only option
4
Q
Starting a Peripheral IV
A
- obtain pt consent and use aseptic technique
- use catheter with flexible cannula when mechanical injector used
5
Q
Using established IV catheter
A
- evaluate if site appropriate for CM
- verify latency with saline flush
- Turn off existing medication only long enough to complete the injection
- Once the CM injection is completed, flush the line with saline and restart medications at the identical pre-examination rate
6
Q
PICC (Peripherally Inserted Central Catheter)
A
- long catheter that is inserted through the large veins of the upper arm & advanced so that its tip is located in the lower one third of the SVC
- some PICC cannot tolerate pressure required for CM injection so instead use separate IV for CM
- If no other IV possible use slowed injection rate and hand bolus instead of mechanical injector
7
Q
nontunneled and tunneled CVCs (central venous catheter)
A
- when possible avoid uses these CVCs for CM and instead starting a standard IV line
- NEVER use a dialysis CVC for CM
8
Q
Documenting CM Administration
A
- documentation of IV contrast administration is a legal necessity
- should include: name of agent, dose (volume and concentration), flow rate, injection site and and adverse effects and their treatment
9
Q
Phases of Tissue Enhancement
A
- CE (contrast enhancement) is determined by the rate the CM is delivered and the time elapsed from injection start and when scanning initiated
- three general phases include: bolus (arterial) phase, non-equilibrium (venous) phase, equilibrium (delayed) phase
- timing and start of each of the phases is affected by injection parameters (shapes of the bolus) and pts cardiac output
10
Q
Bolus (Arterial) Phase
A
- Immediately follows an IV bolus injection
- arterial venous iodine difference (AVID) of 30 HU or more
- Arterial structures are filled with CM, venous structures not yet filled
- a few seconds-30 seconds after injection, 30 sec is optimal time
11
Q
Equilibrium (delayed) Phase
A
- Last phase of tissue enhancement.
- It can begin as early as 2 mins after bolus phase.
- AVID is less than 10 HU.
- CM is mostly emptied from arteries, greatly diluted in the veins, and has soaked the organ parenchyma
- typically 2 minutes or more, some up to 8 mins
11
Q
Drip Infusion
A
- uncommon
- CM is allowed to drip in during a period of several minutes.
- Scanning begins after most, or all, of the CM is in.
- Can be used for routine brain scans, but not appropriate for other examinations
- This is an exception to the general rules of CM injection.
- Injection rate is not important. Brain is imaged during equilibrium phase.
- Scan delay is 4 minutes typically.
- CM must have time to cross the blood-brain barrier.
11
Q
Non-equilibrium (venous) Phase
A
- Follows the bolus phase
- begins approximately 1 minute after the
start of the injection - AVID of 10 to 30 HU
- CM is still in arteries, but also in veins
- typically 1-2 minutes, 60-70 seconds being optimal
12
Q
Hand Bolus
A
- Variable flow rate: because of syringe size, contrast viscosity, IV catheter size, and operator strength
- Results in inconsistent images that are not reproducible
- primarily used when injecting into PICC, tunneled or nontunneled CVCs
13
Q
Pharmacokinetic Factors
A
- factors that affects contrast enhancement
- CM characteristics (concentration, osmolality, viscosity), volume, flow duration, scan delay time and total scan time
- largely controllable
14
Q
Mechanical Injectors
A
- CT injectors may have a single or dual heads for affixing the syringe
- Include a programmable pressure limit
- CM is administered at the selected rate(s), unless pressure reaches the maximum psi set
- Safety precautions must be strictly adhered to precent CM extravasation and air embolism
15
Q
Patient and Equipment Factors Affecting Contrast Enhancement
A
- pt factors: cardiac output, weight
- equipment factors: scanner speed, determined by number of detector rows
16
Q
Test Bolus
A
- method to individualizing the scan delay to adjust to pt factors
- 10 - 20 ml of CM is injected & several trial scans are taken
- To determine the length of time from injection to peak enhancement in a target region (ex. aortic arch for chest, descending aorta for and/liver/pancreas)
- trial scans done on very low mAs and begin from 8-15 seconds after injection start
- scan delay calculated
17
Q
Bolus Triggering
A
- method to individualizing the scan delay to adjust to pt factors
- Use contrast bolus itself to initiate the scan
- A series of low-radiation scans monitor the
progress of the contrast bolus - Measurement of HU in ROI measured before contracts and when ROI reaches peak HU the scan starts
- Once adequate HU is reached, the table moves to the starting level & scanning begins.
- A drawback is that a technologist cannot stay with the patient to monitor the injection site.
18
Q
Saline flush benefits
A
- Flushes out CM that would otherwise be left behind in the injection tubing
- Eliminates the extra step of clearing the vascular access site of residual contrast after injection
- Pushes the contrast bolus forward, so may create a more desirable bolus shape
- Increases the amount of contrast available for use in image acquisition and may reduce artifact
- Decreases amount of CM needed
