CT scans use X-rays to create cross-sectional images of the body. The document discusses the history and principles of CT scanning, describing how images are reconstructed from X-ray absorption data. It outlines the components of a CT scanner including the X-ray tube and detectors. It discusses different generations of CT scanners and how they have improved over time, allowing for faster scan times. The document also covers CT imaging techniques, common artifacts, and applications of CT for evaluating various brain conditions.
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Ct brain presentation
1. Basics of CT scan
by
Chakradhar
Neurology resident
2. HISTORY
Computed tomography (CT) scan machines uses X-rays, a powerful
form of electromagnetic energy.
Sir Godfrey hounsfield-1972
Nobel prize in 1979 with cormack
six generation of scanners
Latest 128 multidetector ct
G.N.HOUNSFIELD ALLAN M. CORMACK
3. PRINCIPLE
Internal structure of an object can be reconstructed from multiple
projections of the object.
Uses x rays applied in sequence of slices across the organ
Images reconstructed from x-ray absorption data
Xray beam moves around the patient in a circular path
Beam of light projected in two
direction's, detecting two different
shadows
4. Terminology
Hounsfield Unit (HU)- mean attenuation of x-rays by
different tissues.
PIXEL & VOXEL
Each square of the image matrix is called pixel
Thickness of block of tissue called voxel
Linear attenuation coefficient
The linear attenuation coefficient ( ) of each pixel is
determined by :
1. Composition of the voxel
2. Thickness of the voxel
3. Quality of the radiation beam
5. Hounsfield units represent logarithmic scale of CT
density.
Pure water has an HU value of ‘0’.
Current CT scans measure from – 1204 to + 3407.
DESCRIPTION Approx. HU DENSITY
Calcium > 1000 Hyperdense
Acute blood 60-80 Hyperdense
Grey matter 38 (32-42) Hyperdense
White matter 30 (22-32) Hyperdense
CSF 0-10 ISODENSE
Fat -30 to - 100 Hypodense
Air - 1000 Hypodense
6. PARTS
1)xray tube-akin to that in a x ray machine.
2)detectors
3)gantry- which houses xray apparatus
4)patient couch
5)viewing console
1.X-ray tube & collimator
2.Detector assembly
3.Tube controller
4.High freq. generator
5.Onboard computer
6.Stationary computer
X ray tube Internal structure of gantry
7. FILTERS
Compensation filter is being used
To absorb low energy x rays
To reduce patient dose
To provide a more uniform beam
9. FIRST GENERATION
Narrow pencil beam
Single detector per slice
Translate –Rotate movements
of Tube- detector
combination
Scan time-5min
Designed only for evaluation
of brain
FIR ST G EN ER A TIO N
10. SECOND GENERATION
Narrow fan beam
(30-100)
Linear detector array(30)
Translate-Rotate movements of
Tube-Detector combination
Fewer linear movements are
needed as there are more
detectors to gather the data.
Between linear movements, the
gantry rotated 30o
Only 6 times the linear
movements got repeated
Scan time~20secs
11. THIRD GENERATION
Rotate(tube)-
Rotate(detectors) Translatory
motion is completely
eliminated
Pulsed wide fan beam(500-
550)
Arc of detectors(600-900)
Detectors are perfectly
aligned with the X-Ray tube
Both Xenon and scintillation
crystal detectors can be used
Scan time< 5secs
12. FOURTH GENERATION
Continuous wide fan beam(500-550)
Ring of detectors(> 2000)
Rotate(tube)-Fixed(detector)
X-ray tube rotates in a circle inside
the detector ring
When the tube is at predescribed
angles, the exposed detectors are
read.
Scan time< 2 secs
13. TYPES
Spiral ct-
uses principle of volumetric acquisiton.
no respiratory misregistration
HRCT
CT cisternography and myelography
14. OTHER SCAN
CONFIGURATIONS
Interest in faster scan times evolves from a
desire to image moving structures such as the
wall of the heart and contrast material in blood
vessel and heart chambers and to overcome
motion artifacts due to cardiac rhythm and
patient breathing .
Dynamic Spatial Reconstructor(DSR)
Electron beam computed tomography
15. DYNAMIC SPATIAL RECONSTRUCTOR
28 X-ray tubes
X-ray tubes are aligned with
28 light amplifiers and TV
cameras that are placed
behind a single curved
fluorescent screen
The gantry rotates about the
patient at a rate of 50 RPM
Data for an image acquired
in about 16 ms.
Reconstruct 250 C.S. images
from each scan data
16. DSR
The Dynamic Spatial Reconstructor (DSR) is a high-temporal
resolution,
studies of cardiovascular structure and function. 3-D dynamic
images can be obtained after reconstruction.
DSR is currently used involves studying selected pediatric patients
with complex congenital heart disease
advantages
Disadvantages
High Cost
Mechanical motion is not eliminated
17. This instrument represents a novel concept in the use of x-ray to obtain fast
tomographic scanning. In contrast to the DSR and conventional CT, EBCT
has no mechanical parts moving around the patients, resulting in lower
heat production and enabling fast scanning.
An electron beam, originating from an electron gun located behind the
patient is magnetically deflected sequentially onto four tungsten target
rings, producing eight fan beams (two from each target ring) of x-ray
radiation that pass through the patient.
Eight almost simultaneous renal tomographic sections can thereby be
obtained,
Electron Beam CT
19. EBCT
Why Is It Done?
This test is used to identify calcium buildup in heart arteries, which
can be a risk factor for coronary artery disease (CAD). It may be
used as a screening tool to detect hardening of the arteries in
people who are at high risk of developing atherosclerosis.
only CT method which can scan the beating
heart.
EBCT in measuring RBF
slices are thicker (8 mm) than those produced by
the DSR.
temporal resolution is lower than that offered by
the DSR (50 or 100 msec/image),
Disadvantages
20. Radiation dose from EBT scans
compared to other sources of
radiation
X ray chest-0.1 mSV
Ct brain-2 mSV
EBCT-0.5 to 0.7 mSV
Environmental radiation per year-0.02 mSV
21. Image Quality in CT
Image quality is the visibility of diagnostically
important structures in the CT image.
The factors that affect CT image quality are
Quantum mottle (noise)
Resolution : Spatial and contrast
Patient exposure.
The factors are all interrelated
22. CT ARTIFACTS
Artifacts are distortions or errors in the
image that are unrelated to the object
scanned .
Most common artifacts in CT are
Motion artifacts
Streak artifacts
Beam hardening artifacts
Partial volume averaging artifacts
Ring artifacts
23. STREAK ARTIFACTS
Cause: Presence and movements
of objects of very high
density(contrast media, metallic
implants,surgical clips)
Appearance: Streaks
REMEDY:-
•Remove the offending object
if possible. Use a smoothing
algorithm. e.g. Standard
algorithm.
28. CECT
To detect abnormal disrution caused by tumor,abscess ,infarct etc
Uses ionic or non ionic contrast(6 fold reduction in allergic reactioin
0.04%)
In normal CNS vessels,pituitary choroid and dura enhance
29. Indications for non ionic contrast
Prior adverse reaction
BA
Allergy or atopy hx
<2yr
RF(Cr>2)
Cardiac
DM
Severe debilitation
30. CT
Advantages –
Easy availabilty
Fast
Better for bone and acute blood,lesions of skull base and calvarium
Calcification
Less limited by patient factors
Disadvantages-
high radiation
poor visualisation of posterior fossa lesions
33. INTERPRETATION OF CT BRAIN
1-GENERAL INFORMATION
2-EXTRACRANIAL TISSUE
3-CRANIAL BONE
4-BLOOD
5-CSF FLOW
A-VENTRICULAR SYSTEM
B-CISTERNS
6-BRAIN TISSUE
A-MASS LESIONS
B-SULCI & GYRI
C-GRY & WHITE DIFFERENTIATION
34. Low density High density
Csf Bone
Fluid Calcification
Air Blood
Fat Contrast
42. Physiologic calcifications
Chorid plexus-rare before 10yrs
Basal ganglia-rare before 40ys
Pineal gland-common after 30 yr rare before 10yr
Falx
Dentate nuclei
43. INDICATIONS
To diagnose neuro infections and their complications
Stroke to distinguish infarct from hemorrhage
Ct angio before thrombolysis
Ct venogram for cerebral venous thrombosis(cvt)
Acute changes in mental status
Focal neurologic findings
Trauma
Suspected SAH
Cns tumors
48. Bacterial meningitis
Indicatations for ct brain
before lumbar puncture-
to look for obstructive hydrocephalus-to prevent herniation
to conform meningeal involvement—by meningeal
enhancement
49. meningitis complications
suggested by seizures, altered sensorium, focal deficits
encephalitis- cerebral edema is seen
others
cerebral abscess
epidural/sub dural empyema
arteritis leading to infarct
hydrocephalus
seen well effaced
Gyri and sulci
Normal parenchyma
cerebral edema
56. Non contrast ct normal or may show complications
On contrast basal enhancing exudates,meningeal anhancement,
tubeculomas with ring enhancement,ependimitis
Basal exudate enhancement
Tuberculomas with perilesional edema
Coalising tuberculomas
58. Stages
vesicular stage- live stage
only hypo dense lesion with out perilesional edema/ring enhancement
colloidal stage- perilesional edema with ring enhancement
granular stage- scolex gets calcified resulting in central hyper density
nodular stage- entire lesion gets calcified nodular stage-
vesicular stage-
colloidal stage- granular stage- nodular stage-
59. Tuberculous granuloma neurocysticercosis
>20 mm size <20mm
large perilesional edema usually small area
irregular margine regular margin
Coalising lesions noncoalising
These findings are not path gnomic,above signs can be seen viceversa
neurocysticercosis
TUBERCULOMAs
central dot sign Stary sky
60. TOXOPLASMOSIS
CT - (70-80 % cases ) multiple B/L hypo dense contrast enhancing focal lesions with
predisposition to the basal ganglia and subcortical region.
A double dose contrast with increased delay scan time may increase the
sensitivity.
62. Why not MRI them all???
- MRI is generally preferable to CT for evaluating intracranial
neoplasms
- CT is preferred for visualizing tumor calcification or intratumor
hemorrhage.
Cns tumors
63. Commonly Calcified and
Hemorrhagic Lesions
Calcified Hemorrhagic
Oligodendroglioma Glioblastoma multiforme
Choroid Plexus tumor Oligodendroglioma
Ependymoma Metastatic:
Central neurocytoma Melanoma
Craniopharyngioma Breast
Teratoma Lung
Chordoma
meningioma