scanner specifics

siemens somatom Force

Dual tube

The scanner has two X-ray tubes that can range kVp from 70-150kVp

Learn more at link below: https://www.siemens-healthineers.com/en-au/computed-tomography/dual-source-ct

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Flash mode

Uses both tubes together to give a high pitch and quick scan time (under 1 second).

Only need 180 degrees of movement for full 360 degrees of information.

Flash mode is useful for

Patients who are unlikely to hold their breath (free breathing)
Patients who are likely to move
CTA’s to capture good contrast enhancement

Flash mode requires a 30cm run up so cannot be used for ECMO patients or for patients

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X-care

Reduces dose to the anterior portion of the scan by up to 40%. Will then ramp up the dose in the rest of the 360 degree arch to compensate.

Used in brain scans to reduce the dose to the orbits.

Only can be used if the patients are positioned straight in the scanner in relation to the chosen position on the scanner.

If the patient is tilted to the side not only is limited dose given to the wrong part, but then increased dose can be given to the orbits.

tin filter

The Tin Filter attentuates lower energy photons to reduce dose and optimize image quality at the interface between soft tissue and air

https://www.siemens-healthineers.com/en-au/computed-tomography/technologies-and-innovations/tin-filter

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FAST integrated worflow

The FAST 3D camera exists above the CT table. When a picture is taken on it, the patient’s shape, positioning, and height is captured in three dimensions through using infrared technology. It allows for the scanner to recognize patient thickness, patient position on table and different regions of the body. You can use the image to select scan range which will then allow an accurate isocentre point and topogram length.

https://www.siemens-healthineers.com/en-au/computed-tomography/technologies-and-innovations/fast-integrated-workflow

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ADMIRE

Advanced Modelled Iterative Reconstruction

Has 5 adjustable strengths: 3 default value, 5 max noise reduction and dose reduction.

ADMIRE values are inbuilt into protocols to ensure for best imaging depending on the anatomy captured.

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IMAR: Iterative Metal Artefact Reduction

Improves appearance of metallic artefacts in CT images. Can be added retrospective to any scan. Negates the need for dual energy metalware artefact reduction

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how do we control mas and kvp on siemens scanners?

Dose modulation (Care dose 4D)

Our scans mA dose modulate based off the topogram. This is called Care Dose 4D on the scanner

This means the mA and kV will change depending on thickness/tissue type detected at particular points of the scan by the topogram.

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Quality reference mAs (Qref) and Reference kV (Ref kV)

The QRef parameter determines the level mA used.

The Reference kV controls the kV level used

Our set Qref and ref kV value describes what mA and kV the scanner would give a average sized 75kg patient

If the patient is less than average as detected by the topogram: The mA and KV given will be less than reference levels

Both are set for each scan protocol to ensure the desired level of image quality and dose reduction is met

Higher QRef: Higher level of image quality required so more mA will be given eg Standard dose head

Lower QRef: Lower level of quality needed so less mA will be given eg Low dose head

CAREkV

The aim of CARE kV is to provide the requested image quality while minimizing dose to the patient.

The CARE kV has 3 different settings

On: the system will recommend the optimal kV based on
- the scan type (C-, C+, CTA) selected on slider
- reference kV
- and patient size on topogram
Semi: a user-defined kV setting eg 100kV chosen for whole scan range by radiographer. Can be useful when you require higher/lower kV than the system is anticipating.

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reconstructions

Filtered Back Projection (FBP)

FBP uses 250,000 + simultaneous equations of ray sums taken at differing angles of a sine wave to compute the values of attenuation coefficients within a cross section

As the name suggests, it is composed of two main steps

filtering the data (along the row direction in the detector)
performing the back projection operation where the data is painted back in the image along the direction which it was measured (9)

Iterative Reconstruction (IR)

The scanner will use a portion of measued projection data and then uses mathematics to fill in the blank data sets with accuracy.

The level of IR used is determined by the ADMIRE setting on the force scanner. Our protocols have been optimised with appropiate ADMIRE levels for the particular scan

Increased IR= less dose and smoother image.

Lower IR= higher dose with noisier image. (6)

Our scanner uses a combination of FBP and IR to make our images