A.Common
Indications :
·
Suspected brain neoplasms, masses,
lesions, or tumors
·
Brain mestastases
·
Intracranial hemorrhage
·
Aneurysm
·
Abscess
·
Brain Atrophy
·
Posttraumatic abnormalities ( such
as epidural and subdural hematomas)
·
Acquires or Congenital abnormalities
(bontrager,2001)
B.Imaging Considerations :
CT imaging of the brain optimally is
completed with and without intravenous contrast enhancement. The non contrast
study of the brain is completed before the intravenous injection of contrast
medium. Contrast injections are sometimes contraindicated for physiologic
reasons such as cerebral trauma and aneurysms. The technologist should be aware
of all contraindications for the use of contrast medium before the examination
of every patient. The type of contrast and dosage to be used is determinate by
yhe facility requirements and manucfacturer’s recommendations.
Upon completion of the non contrast
examination, the technologist should change the image annotation to demonstrate
the injection of contrast medium. When using intravenous contrast medium for
imaging of the brain, The technologist should inject the total amount of
contrast medium before resuming scanning. The same patient position and both
range of slides are similar for second procedure.
When imaging, the technologist
should match the appropriate field of view (FOV) with the patient. The decition
to use conventional or spiral scanning is determined by the imaging facility
and with consideration to the patient’s ability to remain motionless during the
examination. An accurate explanation of the examination process and
consideration of patient comfort will reduce voluntary motion during the
imaging process.
C.Patient preparations
The patient is placed supine and
head first on the examinations table. The head is hyperextended and placed in
the head holder. The head is positioned with the midsagital plane of the
patient parallel with the longitudinal light. The interpupillary line is
parallel with the horizontal positioning lights. The technologist should use
positioning pads and restraining straps as needed. The patient’s arms should be
placed across the abdomen or at thr sides of the patient. To minimize motion
artifacts, the use of restraining straps across the patient’s forehead, chin,
or both, should be considered. Foam padding placed under the patient’s knee can
relieve pressure on the lower back and add to the patient’s comfort, which
reduces the likelihood of patient motion. Thorough but simple instructions
involving the imaging procedure will also reduce patient motion. Proper
placement of radiation shielding is also an essensial part of every CT
examination.
D.Imaging protocol
The first image produced is the
lateral head. From the scout image, the technologist normally selects two
imaging ranges (Neseth,2000). The first range is from the base of skull through
the petrous pyramids. The second range of slices will be from the end of the
first range and extending to the superior aspect of the brain tissue. The slice
thickness in the first range is normally thinner in the comparison to the
second range, to accommodate for artifacts created by the petrous pyramids.
Angulation of axial slices is often determined by radiologist preference.
Certain facilities require the axial slices to be angled parallel with
orbitomeatal line, whereas other facilities prefer and angulation of
15°superior to orbitomeatal line. One of the benefits of angulation is to
reduce the radiation dose to the patient’s eyes and improve visualization of
the posterior fossa. (Neseth,2000).
Figure 1.
Topogram lateral view of head (Hoffer)
A common procedure for a complete
cranial CT scan includes an initial sequence of six to 10 scan takens in axial
sections. These six to 10 scan cover the entire brain, from base to vertex, in
up to 13 millimeter sections. Depending on the scan unit in use, the sections
may be thinner, such as 5, 8, or 10 millimeters, wich requires more scan (5-7
mm sections are common for cranial scans (Bontrager,2001).
In viewing of computed tomography
scans, the patient’s right is placed to the viewer’s left, as in conventional
radiography. Axial scans are viewed as though the viewer were facing the
patient and looking at the scan from the foot end of the patient.
Figure 2. CT axial of brain with trauma
References :
- Neseth Roland, 2000, Procedures and Documentation for CT and MRI, McGraw-Hill Companies.
- Bontrager Kenneth L, 2001, Textbook o Radiographic Positioning and Related Anatomy, Fifth Edition, Mosby, A Harcourt Health Company St. Louis Philadelphia
