Radiology

1. Contrast agents
By Dr paramjeet singh

2. type of contrast agents based on
attenuation of xray
 The positive contrast media attenuate X-rays more than do the body
soft tissues and can be divided into ,
 Water soluble iodine agents.
 Water insoluble barium agents.
 Negative contrast media attenuate X-rays less than do the body soft
tissues.
 Air
 CO2

3. Positive v/s Negative
Positive
contrast
Increased
absorption of
x-rays
Show up as
white
Eg: Barium
Sulphate,
Iodinated
media
Negative
contrast
Decreased
absorption of
x-rays
Show up as
dark
Eg: Air Co2

4. NEGATIVE CONTRAST MEDIA
Mode of action :-Gas displaces, rather than mixing with the blood & they act as a negative
C.M. It rapidly dissolves in the blood and is excreted as it passes through the lungs
 AIR:
 Become obsolete now a days.
 Also used in double contrast studies of the GIT.
Advantage –
o Gets slowly absorbed from the injection site giving more time for imaging.
 Complications - Air embolism

5. POSITIVE CONTRAST MEDIA
Barium sulfate :
 Highly radioopaque.
 Non Absorbable.
 Non toxic.
 Helps in coating the mucosa wall.
 Used in GIT studies.

6. Oily contrast media :
 Used in Myelogram
 Myodil and pantopaque
 Not used now a days due to availability of water soluble agents and
adverse reactions of it.
 Reactions include high incidence of arachnoiditis & oil embolism may
occur if accidentally injected IV.

7. 3.IODINATED RADIOLOGICAL
CONTRAST MEDIA

8. Iodine:
 It is a preferred element in the radiological contrast media
because:
 Iodine has k-shell binding energy (k-edge) of33.2 keV.
 similar to the average energy of x-rays used in diagnostic radiography .
 When the incident x-ray energy is closer to the k-edge of the atom it encounters,
photoelectric absorption is more likely to occur.
 Iodine provides – radio opacity.
 Gives high contrast density due to high atomic number.
 Chemical behavior which allows firm binding to the benzene molecule
 Relatively low toxicity.

9. CLASSIFICATION OF IODINATED CM
 HIGH OSMOLAR / CONVENTIONAL CM
IONIC MONOMERS- salts of Diatrizoate,
Iothalamate,
Metrizoate,
Ioxithalamate.

10. LOW OSMOLAR CONTRAST MEDIA (LOCM)
IONIC DIMER- Ioxaglate(Hexabrix )
Iocarmic acid.
NON- IONIC MONOMERS- Iohexol(Omnipaque),
Iopamidol, mc used
Ioversol(Optiray),
Iopromide(ultravist),
Ioxilan
NON-IONIC DIMER- Iotrolan ( isovist) , least side efefcts
Iodixanol(visipaque).

11.  LOCM also include IOCM (iso-osmolar contrast media)
 Which are non ionic dimer like the iodixanol which is also known as
VISIPAQUE.
How low osmolar are able to bring same level of xray attenuation?
Their dimer structure fits a higher concentration of iodine atoms per osmole,
permitting the diagnostic levels of contrast opacification.

12. Ionic monomers
 The conventional ionic monomers are made up of cations and anions.
 Cation - salts of sodium or meglumine
 Anion -Benzoic acid molecule with 3 atoms of iodine replacing the
hydrogen at C2, C4 and C6 positions(Triiodobenzoic acid).

13.  Diatrizoate and iothalamate are most frequently used.
 They are salts of sodium / meglumine.
 Each molecule completely dissociates in water into 1 anion and 1 cation.
 Each anion contains 3 atoms of iodine hence each molecule of ionic
monomers provides 3 iodine atoms per 2 ions i.e.,iodine : particle ratio of
3:2.

14. Meglumine Sodium
 More soluble
 High viscosity
 Better tolerance
 Does not cross BBB
 Less vascular effects
 Strong diuretic effect
 Poor opacification
 Causes bronchospasm
 Less soluble
 Low viscosity
 Less tolerance
 Crosses BBB
 Marked effects
 less diuretic effect
 Better opacification.
 No bronchospasm

15. Ionic dimers ( LOCM)
 Mixture of sodium and meglumine salts.
 Has double benzene ring – 3 atoms of iodine at C2, C4, and C6 positions.
 Total molecule contains 6 atoms of iodine.
 Iodine : particle ratio 6:2 or 3:1.

16. Nonionic monomers (LOCM)
 Metrizamide – first nonionic tri iodinated monomer.
 Omnipaque(iohexol), ultravist(iopramide).
 They are tri iodinated nonionizing compounds.
 Provide 3 atoms of iodine and 1 osmotically active particle producing
iodine – particle ratio of 3:1.

17. Nonionic dimers(LOCM)
 Iotrolan and iodixanol.
 Iodine: particle ratio of 6:1.
 Still being assessed for myelography, bronchography, and intravascular
usage for their toxicity.
 Iotralan has allergic and skin reactions.

18. Ideal contrast medium should have
 High water solubility
 Heat and chemical stability(shelf life ideally 3.5yrs)
 Biological inertness (non antigenic)
 Low viscosity
 Low/ iso osmolar to plasma
 Safety to lethal dose should be high.
 Reasonable cost.
 90% rapidly eliminated by glomerular filtration by the kidneys
within 12 hours
 10% excreted by-gall bladder, skin, bowel.

19. Pharmacokinetics of Intravascular Contrast
Media
 Pharmacokinetics is the study of what the body does to a medicinal (drug)
product.
 For intravascular products, the processes studied are:
 Distribution
 Metabolism
 Elimination
 Intravascular contrast media do not generally undergo metabolism in the
body.

20.  Intravascular contrast media are excreted almost completely in an
unmetabolised form primarily by filtration at the renal glomerulus.
 Liver & intestine excretes 1% of these compounds.
 Secretion or reabsorption in the tubules is not significant at clinical doses.
 After IV inj, first it diffuses into extravascular space & is simultaneously
excreted.

21.  Plasma half life of contrast is 30 – 60 min
 In patients with normal renal function, the plasma contrast concentration
decreases to 50% the original dose within 2 hours of administration
(elimination half-life) and to 75% within 4 hours
 After 24 hours, 98% of the injected dose will be eliminated by the body.
 The renal excretion of contrast media in patients with renal impairment
and a reduced glomerular filtration rate may last for several days.

22. Dosage of contrast media
 Standard DOSE of iodinated contrast media (LOCM) is 1-2 mL /kg
 Concentration-300 mg/ml
 What is the maximum limit -200 mL with concentration of 320 mg/ml
 IODINE concentration- maximum -64 MG

23. CONTRAST MEDIA RELATED TO
SPECIFIC CLINICAL AREAS

24. Enteric contrast agent
 Barium sulfate is preferred .
 Barium sulfate is not used if perforation is suspected
 May lead to mediastinitis or peritonitis.
 Iodinated low osmolar contrast media can be used in perforation.
Gastrograffin ( low osmolar non ionic contrast is preferred )

25. Renal System
 Recommended dose for I V urography is 15 – 25g iodine.
 High doses will impair renal function causing decrease in renal output
and increased s.creatinine and urea levels.
 HOCM is more Nephrotoxic than LOCM.

26. Risk factors for renal side effects
 Preexisting renal disease and oliguria.
 Diabetic nephropathy.
 Poor hydration.
 Very high doses of contrast medium (given for multiple sequential
examinations that are repeated within a few days).
 Renal dialysis is a effective method and lifesaving for alternative
method of excreting CM.

27. NERVOUS SYSTEM
Cerebral angiography-
 LOCM preferred(if HOCM then-meglumine salts)
Adverse reactions to CM-
 BBB damage - cerebral edema
 Bradycardia
 hypotension

28. Cardiovascular system
Peripheral arteriography
 LOCM are preferred – less warmth, discomfort, pain.
 No need for general anaesthesia.
 Meglumine salts are preferred if HOCM are used – cause less vasodilataion.

29. Pulmonary angiography
 LOCM are preferred
- cause less elevation of pulmonary arterial pressure.
- less coughing and less discomfort.
Aortography
LOCM are preferred since injection of HOCM cause generalised
flushing and vasodilataion.

30. Coronary angiography
 HOCMs with physiological levels of sodium can be used.
 LOCM are more safer since they cause less hemodynamic , myocardial and
physiological changes.
 Contrast media should contain sodium ions whether ionic / nonionic –
reduces the risk of cardiac arrhythmias.

31. Gastro Intestinal Tract
 Water insoluble:
Barium sulphate (used for routine studies)
 Water soluble (iodinated)
Diatrizoic acid (Gastrograffin)
WHY NOT WATER SOLUBLE CONTRAST MEDIA
 Diluted by the intestinal secretions.
 Can get absorbed .
 Mucosal coating is not adequate for double contrast
 Hypertonic – can draw fluid into the lumen – Hypovolemia

32. Specific LOCM used in various type of
contrast studies
 Contrast agent used in myelography –IOHEXOL
 IODIPAMIDE- used in cholangiography
 Iopamidol-used in Angiography
 Ioxaglic acid-used in phlebography

33.  Common names
 Iopamidol-isovue
 Iohexol-omnipaque
 Iopromide-ultravist
 Ioversol-optiray
 Ioxian-oxilan
 Contrast media used in our department (LOCM-IOHEXOL)AKA
OMNIPAQUE

34. Preinjection prepration
 1.Obtain Consent before Contrast Material Injection
 2. take history of prior contrast allergy, drug allergy
 3.If negative proceed if positive can give pretreatment regimen
 4.Document other allergies like asthma and / hay fever
 5.Check serum urea creatinine before contrast administration.
 6.Metformin – should be discontinued 48 hours after intravenous injection
 7.children –Titration according to weight

35. Contrast media guidelines in
renal impairment

37.  Contrast associated AKI: Any AKI occurring within 48 hours after the
administration of contrast media.
 PC-AKI-post contrast AKI is synonym with CA-AKI. Both terms do not imply
casual relationship.
Contrast induced acute kidney injury –CIAKI- it is subset of CA-AKI that can be
casually linked to contrast media administration.
Both are linked as renal impairment hence special protocol needs to be
followed before contrast media administration.

38. PROTOCOL TO BE FOLLOWED IN
PATIENTS with RENAL IMAPAIRMENT
American college of radiology
consensus statement.
 1.which patient to have prophylaxis to prevent AKI
 2.e GFR threshold-30 ml/min/1.73
 3.CKD stage 4/5 a relative contraindication
 4.replacement dialysis advised- N0
 5. Patients with single kidney-treated same as patient with normal bilateral
kidneys
 6.withholding of certain drugs(metformin, aminoglycosides)
 Children – evaluated with bedside schwartz equation not GFR

39.  extra

40. ULTRASOUND CONTRAST AGENTS

41.  Introduction of contrast agents causes increase in the echogenicity of
blood , which can heighten the tissue contrast and better delineate body
cavities.
 The parenteral USG echo enhancers consist of microscopic gas filled
bubbles whose surfaces reflect sound waves.
 The back scattering effect they create due to the different impedances of
gas and liquid increases the echogenicity of blood.
 USG with contrast agents allow us to see image of an organ or lesion
perfusion in real time.

42. Properties of an ideal contrast agent
 Nontoxic .
 Easily eliminated.
 Administered intravenously.
 Pass easily through micro circulation.
 Physically stable.
 Acoustically responsive.

43. Generation of Echo enhancers
 FIRST GEN: Unstabilised bubbles in indocyanine green. Can’t survive
pulmonary passage (only for cardiac & large vein studies)
 SECOND GEN: Longer lasting bubbles coated with shells of protein,
lipids or synthetic polymers.
 THIRD GEN: Encapsulated emulsions or bubbles, offer high reflectivity.

44. TYPES OF AGENTS
 ECHOVIST : First one to be used and contains galactose based
microbubbles.
 LEVOVIST : More stable. Along with galactose based microbubbles,
these are coated with thin layer of palmitic acid.
 CAVISOMES : Gas filled cyanoacrylate microspheres for liver, spleen &
lymph node staging .

45.  MODE OF ACTION : they act in 2 ways
 By their presence in the vascular system, from where they are ultimately
metabolized (blood pool agents)
 By their selective uptake in tissue after a vascular phase

46. Clinical applications
 Contrast media can make vascular studies of perfusion & flow in the
tiny vessels preferable even in machines lacking Doppler capability.
 Contrast can also define vascular architecture surrounding malignant
structures, highlighting abnormal vessels.
 Can be used to study fallopian tube patency & vesicoureteric reflux .

47. Ultrasound contrast in Liver
 Many of these contrast agents show affinity for liver and spleen where
they persist in sinusoids for many minutes.
 This parenchymal “late phase” highlights masses that do not contain
normal liver tissue
ex : metastases.
 Can be used as tracers to provide information regarding hemodynamics
- eg, time delay from hepatic artery to hepatic vein branches

48.  Localizing and characterizing the focal lesions in liver.
 Valuable in monitoring interstitial ablation for presence of residual viable
tumour.
 Detect ischaemic tissue in liver in abdominal trauma
 With microbubbles three types of enhancement patterns are observed
within tumours
1)Diffuse enhancement
2)Peripheral enhancement
3)Non enhancement

49. Ultrasound contrast in Kidney
 Ability to detect the microvasculature has made possible the
detection & discrimination of neovascularisation of RCC from
benign complex cysts.
 Detection of ischaemia in pyelonephritis.
 Useful in large vessel studies- assessing post endograft bleeding in
aortic aneurysm repair and in distinguishing decreased flow from
total carotid occlusion.

50. Ultrasound contrast in Breast
 The exciting development of “micro bubble” pulse inversion contrast
imaging has been used successfull in imaging vascularity in breast.
 Acts purely as “intravascular agents”.
 Angiogenesis mapping using microbubble is a promising technique for
the demonstration of vascular pattern and distribution in Benign and
Malignant breast nodules.
 This non invasive technique would provide prognostic information of
response to chemotherapy and also help monitor response neoadjuvant
or anti - angiogenic therapy of breast tumours.

51. Advantages of Contrast Enhanced USG
 Ultrasound imaging allows real-time evaluation of blood flow.
 Ultrasonic molecular imaging is safer than molecular imaging modalities
such as radionucleotide imaging because it does not involve radiation.
 Alternative molecular imaging modalities, such as MRI, PET, and SPECT
are very costly. Ultrasound, on the other hand, is very cost-efficient and
widely available.
 Since microbubbles can generate such strong signals, a lower
intravenous dosage is needed.

52. Disadvantages of Contrast Enhanced USG
 Microbubbles don’t last very long in circulation.
 They have low circulation residence times because they either get taken
up by immune system cells or get taken up by the liver or spleen even
when they are coated with PEG.
 Ultrasound produces more heat as the frequency increases, so the
ultrasonic frequency must be carefully monitored.
 Targeting ligands can be immunogenic, since current targeting ligands
used in preclinical experiments are derived from animal culture.

53. MRI CONTRAST AGENTS

54. Contrast enhancement in MR imaging is the process of maximizing
the difference of signal intensity b/w two tissues and is achieved by
either increasing or decreasing the signal intensity of a tissue relative to
another.

55. Uses of C.M in MR :
 To differentiate structures.
 To highlight anatomical spaces.
 To provide additional specificity in describing regions of abnormal
signal.
 To depict tissue vascularity & perfusion .

56. Mechanism :
 In MR,contrast agents act by altering the tissue relaxation rates by
changing the local magnetic environment.
 MR is unique in that there are multiple parameters responsible for
signal intensity.
 So the contrast agent must have the ability to influence these
parameters at low concentration to minimize dose and potential
toxicity.

57. Parameters determining MR signal intensity and
contrast
1. Proton density.
2. T1 & T2 relaxation times.
3. Magnetic susceptibility.
4. Diffusion & Perfusion.

58. Spin density : Can’t be altered significantly by a
contrast agent.
Relaxivity:
 Two relaxivity parameters that are unique to each tissue are T1 and T2.
T1 - the longitudinal /spin lattice relaxation time.
T2 – the transverse/spin relaxation time.
 Contrast enhancement depends upon the alteration of these two
relaxivity parameters.

59.  They can be categorized on the basis of relative change each
impart on either T1 & T2.
T1 agents / positive relaxation agents :
• Predominantly affects T1 relaxation.
• Enhanced T1 relaxation results in increased signal intensity on
T1WI.
T2agents / negative relaxation agents :
• Predominantly affects T2 relaxation.
• T2 shortening causes decreased signal intensity on T2WI.

60.  3 agents have been approved by FDA.
They are
 Gd-Hp-DO3A (Gadoteridol)/Pro Hance) - non Ionic
 Gd-DTPA (Gadopentetate dimeglumine/ Magnavist) –
Ionic
 Gd-DTPA –BMA (Gadodiamide/Omniscan) –
Non Ionic.

61. T2 relaxation agents:
 Super paramagnetic agents.
 Of the ferrite particles, magnetite (Fe3O4) is used commonly.
 These are crystalline oxides with particle size ranges from 0.5 –
1microns.
 Used in the study of liver, spleen & GIT.

62. THANK YOU