Clare StevensChief CT Technologist

Pacific Radiology

Christchurch

8:30 - 9:25 WS #145: Non Invasive Coronary Assessment

9:35 - 10:30 WS #155: Non Invasive Coronary Assessment (Repeated)

Dr Ross KeenanRadiologist & Director

Christchurch Radiology Group

Christchurch

Cardiac CT Procedure

Clare Stevens

CT MRT

Cardiac CT at Pacific Radiology

Carried out in the new department at St Georges Radiology

• New Siemens Drive CT Scanner

• Patient preparation and experience

• Scanning techniques

• Software and Post processing

Siemens SOMATOM Drive CT Scanner

• Installed in March 2017

• Latest technology from Siemens

• 128 slice

• Dual Tube – 2 x Xray tubes and Detectors

Siemens SOMATOM Drive CT Scanner

This technology enables:

• Lower radiation doses

• Sub mSv scans, dependent on patient Heart Rate

• Less contrast – Used to use 90-110mls now 50-70mls

• Faster scanning – Not just the total scan time to acquire the heart but the all important Temporal resolution which allows an image to be created from 75ms of data – with 2 tubes only 90° of data needed to create an image

• Shorter breatholds 5-10s

• Scanning patients with AF or fast and variable HR

The Patient

Patient Preparation

All about keeping them relaxed and the HR steadyPatient must have no alcohol or caffeine for 4 hours before appointment and should not smoke for at least 2 hours before appointment.They are asked to take all other medications and eat all meals as usualWe ask them to allow 2 hours for the appointment – patients in a hurry do not have a steady HR !

Patient Preparation

Prior to scan• Changed into a gown• Procedure Explained – we take care to make sure that

there are “no surprises”• IV Contrast Consent – explain sensations - hot flush,

metallic taste and the patient would be very alarmed, if they were not aware, when they experienced the sensation like they had “wet their pants” – that would surely raise the HR !!

• 18G IV cannula inserted into antecubital vein - High pressure injection of 60-80mls contrast plus saline “chase”

Patient PreparationPositioned on the table• Feet first, arms above head, ensuring as

comfortable as possible• ECG leads positioned• Practice Breathold – Patients HR will rise

when taking a breath in and will fall and steady as they hold their breath - Max 10 secs total required

• HR assessed – Steady, low HR is ideal• Beta Block if required – 100mg

Metroprolol standard• Different acquisition technique will be

used dependent on the patients HR range and variability

Use of Beta Blockers

Beta Blockers are used to steady and/or lower the Heart Rate for higher quality and lower dose acquisitionDependent on the age of the patient a HR range will be aimed for, this will define the scanning technique used:•

The Acquisition

Acquisition Routine

1. Planning Scan

2. Calcium Score

3. Test Injection and Contrast timing scan

4. Coronary Angiogram

Acquisition TechniquesFlash ModeAdvantages• Enables ultra low dose (sub mSv)

acquisition of whole heart in 0.48ms, one beat

• Patient moves very fast through the gantry – 46 cm/s

•

Acquisition Techniques

Flash ModeDisadvantages• HR must be below 60 Bpm• Must be stable – within 3 Bpm• Once the contrast injection is started we are

at the “mercy” of the patients HR !• If it rises above 60 Bpm during the 20 or so

seconds it takes the contrast to reach the heart there can be blurring of vessels and repeat scans needed

Acquisition Techniques

ProspectiveHeart beat triggers the acquisition during a set range of the HR cycle e.g. 60-80% of the RR interval

• Used for 60-75Bpm• Scanned over 3-4 Heart Beats –Table moves in steps• Higher dose – up to 5mSv•

Acquisition Techniques

Prospective – Millisecond SystolicWe set the acquisition range to be a set ms range from the R peak• Used for Erratic or Fast HR• Atrial Fibrilation• 75-90Bpm

Acquisition Techniques

RetrospectiveSpiral acquisition across a wider range of the heart cycle, thus applying more radiation dose – the data is then reconstructed into the required phases post scan• > 90 Bpm• Highest Dose• Both Systolic and Diastolic acquired• Data can be reconstructed at different phases of the Heart Cycle to “piece

together” stationary vessels• Very unusual for us to need to use this technique with this new scanner

Acquisition Techniques

If HR changes during prospective or Retrospective acquisition we can use the software reconstruct the data at a different phase of the Heart Cycle

Not possible in “Flash” mode –you “get what you’re given”

Software

Additional Software

Care kV – kV adjustmentScanner will “Suggest” kV selection to optimise contrast within the image and enable “dose reduction”

iMAR – Metal artefact reductionReconstruction algorithm to reduce the artefact caused by metal implants of all kinds

ADMIRE – Itterative ReconstructionNoise reduction reconstruction, number of iterations can be adjusted by the userEnables lower doses with acceptable noise in the image

Post Processing

Calcium ScoreVery Low dose scan (HR dependent)Calcium in each coronary artery is highlighted by the tech and measured by the software

Post Processing

CTCASemi automated software for tracing vesselsPreparation by CT Techs for Radiologists reporting

Post Processing

CTCAVessel evaluation by Radiologist in reporting process

Post Processing

CTCAPresentation of images for referrer

That is Cardiac CT Process at Pacific Radiology