2. Definition
Contrast media — or just ―contrast‖ — is a clear liquid
that highlights certain parts of your body on imaging
tests. In terms of CT the substrate for contrast is iodine. Due
to its high atomic number (53), and its interactivity with xradiation (X-rays) iodine is an excellent element for being
able to differentiate between various tissues of the body
and how blood is transmitted through those tissues.
3. Uses in CT
There are many different uses of contrast in CT. We utilize
intravascular contrast agents for visualization of vascular structures
and specific organ pathology. Oral contrast media is for defining
gastrointestinal pathology. The administration of contrast either
oral or intravascular is all about timing, when to image the patient
in relation to the structures we wish to image based upon how a
patient presents themselves to us as technologists. The following is
a list of some CT protocols and the associated timings.
4. CT Protocols and Contrast Timing
• CTA (CT Angiogram) – is a study of vascular structures and is an
arterial study, therefore the timing will be consistent with arterial
blood flow. For example if we are interested in imaging the
carotid structures in the neck, our timing would generally be
between 18 – 22 seconds from the introduction of the contrast
media.
• CTV (CT Venogram) – is a study a vascular structures and is a
venous study. It is different in terms of timing based on physiology,
specifically blood flow patterns. Refer to the cardiac cycle for a
refresher, if needed. Timing can range from around 45 – 120
seconds depending on the region to be imaged.
5. CT Protocols and Contrast Timing
• CT Chest – a study of the structures within the thoracic region and 40 –
50 seconds is usually sufficient for visualization.
• CT Abdomen – a study of the abdominal structures and 50 – 70 seconds is
usually sufficient for intravascular contrast. Oral contrast (Barium
Sulfate, Gastroview, Gastrografin) require approximately 1- 2 hours for
full opacification of the intestinal tract.
• CT Pelvis - a study of the pelvic structures and 50 – 70 seconds is usually
sufficient for intravascular contrast. Oral contrast (Barium Sulfate,
Gastroview, Gastrografin) require approximately 1- 2 hours for full
opacification of the intestinal tract. Rectal contrast can also be
administered for this study and no wait time is required.
6. CT Protocols and Contrast Timing
• CT Soft Tissue Neck – a study of the structures of the neck
generally including from the aortic arch through the Circle of
Willis. Timing for intravascular contrast should be between 40 and
50 seconds. Oral contrast can be administered by having the
patient swallow a mouthful of contrast just before image
acquisition is to begin.
• CTA Chest (PE) – A study of the pulmonary artery and its segmental
branches. Timing of intravascular contrast should be between 6 –
10 seconds for optimal arterial opacification. Imaging should be
triggered utilizing a HU (Hounsfield Unit) threshold method.
7. CT Protocols and Contrast Timing
• CT Urgography – This protocol requires multiple imaging sets of
the same region. Various techniques exist from scanning each
phase independently to using a Split Bolus techinique. The phases
of acquisition are: Non-Contrast, Cortico-Medullary, nephrographic
and excretory phases.
• Corticomedullary Phase (25-50sec)
• Nephrographic Phase (60-140 sec)
• Excretory Phase (4-8 minutes)
8. CT Protocols and Contrast Timing
• CT Enterography - a study that uses CT imagery and a contrast material
(Volumen) for a better view of the interior of the small intestine.
• 3- 450ml bottles of volume administered 20 minutes apart
• Inject intravascular contrast (Omin 350, Isovue 370, Ultravist 370) as if doing a
CTA Abdomen (20 – 25 seconds)
• CT Triple phase liver - performed in cases of surveillance or follow-up for
hepatocellular carcinoma in patients with chronic liver disease/cirrhosis
and follow-up after chemoembolization of liver malignancy (primary or
metastatic) and in patients who have had a liver transplant.
• Arterial phase usual delay 30 sec Ideally obtain excellent hepatic arterial
opacification with minimal contrast in portal vein
• Portal venous phase –70 sec
• Equilibrium Phase - 180 sec
9. CT Protocols and Contrast Timing
• Certainly this does not represent a complete and absolute list of
CT protocols however the previous slides represent general
aspects of the contrast timings, as with any protocol it is
dependent upon a number of factors including the patient
physiology, radiologist, and equipment. Always take these things
into consideration when deciding on your timings. Today, many
equipment vendors have vastly improved their technology to help
take out the guess work in some of these areas.
10. Contraindications
• There are reasons which are patient dependent in which the use
of IV contrast is not be used or further consultation should be
taken under advisement – these are called contraindications. Here
is a list:
• Pheochromocytoma– IV contrast may precipitate a hypertensive crisis
• Allergies– Patients with allergies have twice the risk of contrast reactions
compared to the average patient
• Allergic Asthma– Patients with asthma have five times the risk of contrast
reactions compared to the average patient
11. Contraindications
• IL-2 (Interleukin - 2 Chemotherapy)– Patients who are currently on IL-2, or
have received IL-2 in the recent past, have an increased risk of delayed
reaction. The reaction generally occurs several hours after the injection,
and can be mild to severe. Symptoms can include hives, rash, pruritis,
fever, chills, joint pain, flu-like symptoms, tachycardia,or hypotension.
• Diabetes– elevated creatinine, renal insufficiency
• Renal Failure
• Nephrectomy
• Renal Transplant
• Glucophage/Metformin- an oral antihyperglycemic medication that in
combination with IV contrast can cause acute renal failure, lactic acidosis,
or death.
12. Contraindications
• Active Gout – a disease that causes hyperuricemia.The patient needs to have a normal
creatinine level and not be dehydrated prior to receiving IV contrast, to reduce the risk
of acute renal failure.
• Multiple Myeloma– a malignant bone condition that causes kidney failure,
dysproteinemia, abnormal proteins in the plasma, and abnormal urine proteins (Bence
Jones proteins). IV contrast may cause the proteins to precipitate resulting in renal
tubular obstruction and possibly renal failure. Multiple myeloma is only considered a risk
factor for contrast nephrotoxicity when combined with pre-existing renal insufficiency.
• Proper screening of patients will ensure reduced risk of an event occurring. In
certain circumstances pre-medication of patients with a corticosteroid will
reduce a potentially life threatening situation while still obtaining diagnostic
images.
• For a more in depth and complete explanation please refer to ACR Manual on
Contrast Media
