Brain CT

2009-06-04T10:58:00.000-07:00

INTRODUCTION :

The brain CT scan is the most common and falsely regarded easiest CT scan that you will perform. It is very important that CT brain scanning is thoroughly covered and understood.

It really is the ‘bread and butter’ of the CT radiographer. Scan protocols need to be varied for different pathologies and scan parameters changed to get the best possible images for all the different types of patients.

The vast majority of brain CT scans are performed in the axial plane. The coronal plane may be required in some cases to better demonstrate a patient’s pathology.

All scans should start with no IV contrast media. The addition of IV contrast media can hide some brain pathologies that involve calcification or bleeding.

The introduction of IV contrast media aids in the differential diagnosis of brain lesions. It helps demonstrate pathologies like a brain abscesses or tumours.

As always, patients need to be screened to determine if IV contrast media is contraindicated

To decrease radiation dose some institutions will only do a post IV contrast scan on paediatric patients.

The dose of IV contrast media for CT head imaging varies between 30-50 ml of 300-350 (300-350 mg iodine per ml) strength contrast. For paediatric patients a dose of 1.5 ml per kilogram (up to a total of 30 ml) of 300 strength is sufficient.

Patient Positioning :

Patients need to be positioned so that they are comfortable and do not move during the CT scan.

The 'scout' radiograph must include all relevant anatomy that is to be imaged.

Axial Positioning

Topogram
Axial
lateral topogram/
scout
(to include entire head)

Examination

axial brain
axial sinuses
axial facial bones
axial orbits
axial temporal bones axial pituitary fossa
(refer figure 1)

Patient Positioning
- use head holder
- patient positioned supine, head first
- chin angled down slightly
- arms by patient’s side or across chest
- use Velcro straps and immobilisation
pads to help the patient keep his/her
head still
- if the patient is likely to jump off table
use thick Velcro straps and strap the
patient down to the table
- ensure that patient is comfortable

Coronal Positioning
Topogram
Coronal
lateral topogram/
scout
(to include entire head)

Examination
coronal pituitary fossa
coronal sinuses
coronal facial bones
coronal temporal bones
coronal orbits
(refer figures 2 & 3)

Patient Positioning
- use head holder
- patient positioned prone, head first,
with neck extended
- arms by patient’s side, so as not to get
caught up in the moving table
- use Velcro straps and immobilisation
pads to help the patient keep his/her
head still
- if patient is likely to jump off table use
thick Velcro straps and strap the
patient down to the table
- ensure that patient is comfortable

Pitfalls
There are a number of pitfalls to be aware of when scanning the head region. Coronal scans should always be performed as quickly as possible. It is generally very hard for a patient to stay still in this difficult and uncomfortable position.
When performing coronal scans dental fillings may cause severe artefact on the resultant images. Techniques to decrease artefact impact may be to vary the gantry tilt or remove the false teeth, which are causing the problem.
¡It is very hard to remove the beam hardening artefact which degrades image quality in the posterior fossa. Some scanners are better than others at removing it. Using thin slice collimation and special artefact reduction algorithms can help decrease this problem. MRI has a great advantage over CT scanning in this respect.
¡However the greatest pitfall of all is the CT radiographers lack of concentration. It is a wise idea to always double-check all your work so no silly mistakes are made.

BRAIN CT

Brain CT