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2280: CT > Week 4: Injection Techniques > Flashcards

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
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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

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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
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4
Q

Starting a Peripheral IV

A
  • obtain pt consent and use aseptic technique
  • use catheter with flexible cannula when mechanical injector used
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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
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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
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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
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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
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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
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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
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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
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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.
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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
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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
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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
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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

2280: CT (13 decks)

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