A brief overview of various protocols in CT positioning anc the use of different types of contrast media.

1. CT POSITIONING PROTOCOLS,
CONTRAST PROTOCOLS

2. OVERVIEW OF CT IMAGING AND ITS
IMPORTANCE IN BRAIN DIAGNOSTICS.
 CT Brain provides cross-sectional views of the brain’s structure
 It helps in identifying traumatic damage, bleeding and infections affecting
the brain with great accuracy
 CT Angiography helps in evaluating blood vessels, detecting aneurysms,
blockages and malformations of the brain
 It provides support in early diagnosis and improves treatment outcome
significantly.

3. PATIENT PREPARATION, POSITIONING
AND EQUIPMENTS
 Ensure fasting of the patient and remove all metal objects
 Patient is supine with head straight and secured in headrest
 Align laser light with anatomical landmarks for precise positioning
 Perform a scout image to verify the positioning
 CT scanner is set according to protocol and imaging requirements

4. CT SETTINGS
 Image Mode : Use axial or helical mode
 Slice Thickness : Set between 0.6 - 5 mm
 Scan Range : Covers the region under interest
 Tube Voltage : Commonly set at 150 kVp
 Tube Current : Adjust based on patient size, between 200 to 400 mA
 Scan Timing : Dependent on organ under review
 Reconstruction Algorithm
 Post processing

5. RECONSTRUCTION ALGORITHMS
 Filtered Back Projection :
 A traditional method that uses convolution filters to reduce blurring and reconstructs
images quickly.
 It is used widely but can introduce noise and artifacts
 Iterative Reconstruction :
 A modern approach that starts with an initial image assumption and refines it through
multiple iterations.
 It reduces noise and improves image quality while minimizing radiation dose.
 Model Based Iterative Reconstruction
 A more advanced version of iterative reconstruction incorporating statistical modelling,
physics and optics
 Provides superior image clarity and accuracy, esp in low dose scan

6.  Cone Beam Reconstruction
 These are specifically designed for cone beam CT scanners, this algorithm
processes data from multiple angels to create 3D images
 Deep Learning Based Recontruction
 Convolutional neural networks (CNNs), are trained on large datasets to learn
patterns and features in medical images. These models can reconstruct high-
quality images from raw or noisy data.
 This newer cutting edge approach is currently gaining traction in modern CT
Imaging

8. CT POSITIONING FOR HEAD IMAGING
 Patient positioning – patient lies supine on CT table with head placed in
headrest for stability, aligned in the midline, ensuring no tilt or rotation
 The chin is slightly tucked to align the orbitomeatal line (OML)
perpendicular to the table
 Landmark
 External landmark – External auditory meatus and outer canthus of eye
 Internal landmark – The base of skull and vertex
 Location
 Start – Base of skull (foramen magnum)
 End – Vertex of skull

10. CT POSITIONING IN CERVICAL SPINE
 Patient positioning – Patient lies supine with head, neck aligned to midline
 Arms are positioned alongside body with shoulders pulled down
 Landmarks
 External – Sternal notch and external auditory meatus
 Internal – Hyoid bone and thyroid cartilage
 Locations
 Start – Base of the skull to include upper cervical spine and pharynx
 End – Extends to thoracic inlet covering lower spine

12. CT POSITIONING IN CHEST
 Patient positioning – patient supine
 Both arms raised above head to reduce interference in chest region
 Landmarks
 External – Sternal notch (manubrium) and xiphoid process
 Internal – apex of lung and diaphragm level
 Location
 Start – Begins at apex of lung (just above thoracic inlet)
 End – Extends to costophrenic angles (just below the diaphragm)
 Patient is instructed to hold the breath to minimize motion artifacts
 Confirm field of view (FOV) to ensure both lungs and mediastinum are incl.

15. CT POSITIONING IN ABDOMEN
 Patient positioning – Lies supine
 Arms are placed overhead
 Landmarks
 External – xiphoid process (upper landmark) and pubic symphasis (lower
landmark)
 Internal – Including liver, kidneys, pancreas, spleen, bowel loops
 Scan Location
 Start - Above dome of diaphragm
 End – Extend iliac crest or pubic symphasis

17. CT Angiography of Head, Neck, Chest and Abdomen
CT Contrast Protocols

19.  Used for enhancing visibility of blood vessels, tissues and abnormalities
 Primarily Iodinated contrast are used
 Ionic – Diatriazoate, iothalamate, metrizoate
 Non ionic – iohexol, iopamidol, iodixanol (Pref due to less ADR)
 Osmolarity
 High Osmolality – Older agents, high ADR
 Low Osmolality – Newer agent, safer, widely used.

20. What to tell the patient before giving
contrast?
“Normal anatomy on CT Scan is all grey. Air shows up black, and bone
shows up bright white. Without any kind of contrast, All the blood vessels in
your brain will appear grey. The contrast agent will help to highlight the
blood vessels and any problems associated with it. It will also highlight any
kind of infection or inflammation or bleeding. So if there’s anything going on
in there, chances are, I’m going to be able to see it. The IV contrast will give
you a warm feeling all over, but sometimes it’ll vary from person to person. It
will also give you a little bit of a metal taste. This is all normal. Sometimes the
contrast will make people a little bit noxious, but if you have any kind of
problems, please, let me know. Do you have any questions?”

21. Preparation for CT angio Patient
 Fasting
 Hydration
 Medication Review
 Contrast Allergy check
 RFT (BUN and creatinine)
 IV Placement
 Comfortable clothing
 Breath hold Practice

22. Medication Review
 Beta Blockers
 Lower heart rate for better clarity esp for cardiac CT angiography
 Nitroglycerine
 Dilate coronary arteries, enhancing vessel visualization
 AntiHistamine and Steroids
 Premedicate in patients with contrast allergies to reduce reaction risk
 Anticoagulants
 Review to assess bleeding risk esp if invasive procedures are planned post
angiography

23. Review of Metformin in CT
Angiography
 Rare but serious risk of Metformin Associated Lactic Acidosis (MALA)
 Mechanism :
 Iodinated contrast can temporarily affect kidney function leading to reduced
clearance of metformin and accumulation of lactate which may trigger lactic
acidosis
 Pre Procedure Guidelines:
 Assess RFT by test like serum creatinine or GFR
 Discontinue metformin 24 to 48 hours before producer if GFR < 30 ml/min/1.73 m2
 Post Procedure Guidelines:
 Reassess RFT 48 hours after procedure
 Resume metformin only if RFT is stable and within normal limits

24. Impact of breath holding on various
Imaging
 Motion reduction
 Minimize respiratory motion, prevents blurring and motion artifacts
 Improved Clarity
 Blood vessels and organs appear sharper and more defined
 Accurate Alignment
 Essential for studies like CT Angiography where precise timing with contrast
injection is critical
 Patient Compliance
 Provides consistent and reproducible imagine results

25. When to capture Images?
 After giving contrast through IV, it travels up the arm to the heart and then
to the brain and other organs. To catch the images we need to capture
contrast in its desired phase.
 Usually this is during the venous phase as both veins and arteries have
contrast
 Timing helps to capture the images at the right moment

26. Phases of enhancement
 The purpose of CECT is to find lesion which many be hypovascular or
hypervascular as compared to the normal tissue.
 The various phases help in identifying and highlighting certain tissues which
take up or lose contrast as per its corresponding uptake.

27. Non-enhanced CT
• Detection of calcifications, fat in tumors, fat stranding in inflammations like appendicitis,
diverticulitis
Early arterial phase
• Contrast is still in arteries and has not enhanced organs or soft tissues
Late arterial phase
• Structures receiving blood supply will show optimal enhancement
Hepatic or late portal phase
• Liver parenchyma enhances through portal vein blood supply
Nephrogenic phase
• All of renal parenchyma enhances including medulla enhances.
Delayed phase
• Wash out of contrast in abdominal structures except for fibrotic tissue

28. IV contrast timings

31. Hounsfield Units
 Hounsfield Units (HU) are a scale used in CT imaging to measure tissue
density relative to water.
 Water is assigned 0 HU, air is -1000 HU, and dense structures like bone range
up to +1000 HU or more. Different tissues have specific HU values, aiding in
differentiation.
 The human eye can only differentiate upto 20 shades of grey effectively
 CT images contain upto 256 shades of grey which make it difficult for
interpretation of CT images

32. Windows settings
 To adjust the HU range displayed on the image
 Window Level (WL)
 Center of HU range tailored to the tissue of interest
 Eg. 40 HU for the brain
 Window Width (WW)
 Determines the range of HU displayed, controlling contrast
 Eg. Narrow width for soft tissues, wide width for bone

33. Windows in CT imaging of Head and
Brain
 Different windows are used to optimize
visualization of specific structures
 Brain window :
 Window width : 80 HU
 Window level : 40 HU
 Evaluated brain parenchyma for abnormalities
like infarctions
 Bone window :
 Window width : 2000 HU
 Window level : 400 HU
 Highlights bony structures useful for detecting
fracture or bone lesions

34.  Subdural window :
 Window width : 80 HU
Window level : 40 HU
 Optimized for detecting subdural
hematomas or subtle hemorrhages
 Stroke window :
 Window width : 80 HU
Window level : 40 HU
 Enhances visualization of early ischemic
changes in stroke evaluation

35. CT Positioning in Head with Contrast
Position / Landmark Center on patient’s chin
Scan Start Below base of skull (foramen magnum)
Scan End Vertex of the skull
Breath Hold None
IV Access 22 G or larger, antecubital
IV Contrast Adult 100 ml OMNI 300 @ 2.0mL/ sec
Contrast Delay Scan 5 minutes from Start of Injection

36. Indications for CT Angiography of
Head
 Intracranial aneurysm
 Cerebral Parenchymal Hemorrhages
 Arteriovenous malformations
 Sub Arachnoid Hemorrhages
 Neoplastic surgeries

37. CT Angiography Head and Neck
Position / Landmark Level of Aortic Arch
Scan Start Below Aortic Arch
Scan End Above Skull
Breath hold None
IV Access 20 G or larger, Antecubital
IV Contrast Adults 50 ml OMNI 350 @ 5.0 ml/sec
Contrast Delay Bolus Tracked : Trigger Scan @ 120 HU

38. Indications for CT Angiography of Head and
Neck
 Ischemic Stroke
 Transient Ischemic Attack
 Sub Arachnoid Hemorrhage
 Vascular dissections
 Trauma

39. CT positioning in Chest with Contrast
Position / Landmark Supine centered above the lung
apices
Scout Scan Start Above lung apices
Scout Scan End Adrenals / upper kidneys
Breath hold Inspiration
IV Access 18G -22G
Location: No lower than 2” below the
AC crease of the elbow, pressure
approved TLC, PICC lines,
(NOTE: For PV IV flush with the arm in
the position it will be for the scan)
IV Contrast Adults OMNI 350 80 ml
Contrast Delay 60 sec

40. Indications for CE CT Chest
 Suspected cases of lung cancer and staging
purposes
 Thoracic vascular diseases
 Pulmonary Parenchymal diseases
 Pleural diseases
 Airway evaluation
 Sternal and Mediastinal infections

41. ADR associated to Contrast
 Idiosynscratic reactions
 Mild : scattered urticarial rashes, pruritis, retching,
 Moderate : Vomiting, facial edema, tachycardia
 Severe : arrhythmias, laryngeal edema, pulmonary edema, seizures
 Nonidiosyncratic reactions :
 Mostly due heightened sympathetic activity : bradycardia, hypotension, and
vasovagal reactions; neuropathy; cardiovascular reactions; extravasation; and
delayed reactions.
 Other nonidiosyncratic reactions include sensations of warmth, a metallic taste in
the mouth, and nausea and vomiting.

42. Management of ADR in CECT
 For any reactions : STOP CONTRAST ADMINISTRATION
 Depending upon severity of the reaction (One or more steps to be followed):
 Call for help
 Airway , Breathing, Circulation
 Epinephrine Administration ( 0.3 – 0.5 mg )
 Antihistamines : Inj Chlorpheniramine maleate (25 -50 mg)
 Corticosteroids : Inj Hydrocortisone (100 mg)
 Bronchodilators : B2 agoinst
 IV Fluids
 Monitor, document and follow up

43. Specific ADR
 Nephropathy :
 Elevation of 0.5 mg% or more than baseline of creatinine after 1-3 days after
ICM injections. The elevation reaches peak by 7 days and returns to normal
by 14 days.
 Incidence is estimated around 2-7 % of population.
 Post sequelae of is persistent decrease of renal function in upto 25% patients
 Cardiovascular reactions :
 Due to vasovagal reactions due to anaphylactic reactions
 Bradycardia with peripheral vasodilation with lower threshold for ventricular
arrhythmias and cardiac arrest in severe cases.
 Majority cases are self limiting but can be an indicator of a more severe
evolving reactions

44. Management of Contrast associated Nephropathy
 Monitor RFT
 Supportive care : Provide fluids to maintain hydration and kidney function
 Dialysis in severe case
 Renal Replacement therapy
 Avoid further contrast exposure