Risks of Ionizing
Radiation, Contrast, and
More in Diagnostic
Imaging
Jon Hallstrom MS3
OHSU December 2006
Importance and Purpose
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Diagnostic imaging has an expanding role and utility, and
the management of nearly every inpatient is now affected
by information obtained from imaging.
In general, risks are quite low compared with potential
benefit. However, many procedures are performed unnecessarily
with risks of imaging and appropriateness guidelines neglected,
in part due to overburdened health workers’ need for “timeefficient” care and growing medico-legal issues.
This presentation hopes to summarily identify and characterize
risks associated with diagnostic imaging modalities with
emphasis on radiation biology, or the study of effects of ionizing
radiation, and adverse reactions to contrast agents.
Case Study—The

Created by Stan Lee and Jack Kirby, the Hulk first
appeared in Marvel Comics’ Incredible Hulk # 1
(May 1962).

After nuclear physicist Dr. Robert Bruce Banner is
caught in the blast of a gamma bomb he
created, he is transformed into the Hulk, a raging
monstrosity.

The Hulk possesses immense levels of physical
strength… the Hulk's "capacity for physical
strength is potentially limitless due to the fact that
the Hulk's strength increases proportionally with
his level of great emotional stress, anger in
particular."

The Hulk's primary physical rival, the
Abomination, is also gamma-spawned. He, like
Bruce Banner, belongs to the small minority of
people who are born with a genetic factor that
cause them to change instead of being killed by the
radiation.
1. From www.wikipedia.com “Hulk (Comics)”
1
Hulk
Outline
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Background Radiation
Ionizing Radiation
Physics and biology
 Radiation Dose
 Carcinogenesis
 Hereditary consequences
 Embryologic/Fetal effects
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Contrast Media
MRI, Ultrasound
Background

1
Radiation
Background radiation:
Estimated at 2.4mSv per year
with a range of 1-10
 Approximately half is due to radon inhalation
 Man-made radiation accounts for 18% of annual
radiation exposure in the US, with medical X-rays
and Gamma-rays accounting for 79% of artificial
sources

1. Health Risks From Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2 2006.
Background
1
Radiation
1. Health Risks From Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2 2006.
Ionizing

1,2,3
Radiation
Physics of Radiation
Diagnostic imaging utilizes X-rays
and Gamma-rays, two forms of high
energy, electromagnetic, indirectlyionizing radiation
 Ionization refers to the ability of X-rays or
Gamma-rays, when absorbed by target tissues,
to eject orbital electrons from an atom or
molecule

1. Hall’s Radiobiology for the Radiologist, Sixth Edition 2006.
2. Health Risks From Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2 2006.
3. Fajardo’s Radiation Pathology 2001.
Ionizing Radiation
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X-rays
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Artificially produced by
anode bombardment of
accelerated electrons in
cathode ray tube
Transmission radiation
Used in radiography,
including CT,
angiography, fluoroscopy

Gamma-rays
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Formed following
electron capture or alpha
or beta particle emission
from unstable
radionuclides
Emission radiation
Used in nuclear imaging
studies
• X-rays and Gamma-rays may be considered identical for any given energy wavelength
• X-rays and Gamma-rays are considered low linear transfer of energy (LET) radiation
because they have a slow rate of energy transfer and are sparsely ionizing compared with
particulate directly ionizing radiation
Ionizing Radiation
X-rays being generated by anode bombardment of electrons?
Actually, we are looking at the USS Enterprise, a galaxy class
starship, entering warp speed.
Ionizing Radiation

Biology of X-rays and Gamma-rays


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May directly ionize a target molecule or indirectly affect target
molecules by free radical formation with propagation
Effects may extend beyond irradiated cells, particularly via
intercellular gap junctions, known as the “bystander effect”
Genomic damage consists of chromosomal aberrations,
instability, and gene mutations
Degree of damage may be affected by stage of cell cycle,
hypersensitivity (eg hypoxic states), and protective agents (eg
antioxidants)
Cells may attempt repair (eg DNA excision repair) or
undergo apoptosis, but are not always successful
Ionizing Radiation

Radiation Dose
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Absorbed dose: the ratio of energy imparted to the mass of the
exposed body or organ, measured in gray (Gy = J/kg)
Equivalent dose: Accounts for variation in the degree of tissue
damage created by different types of radiation (eg alpha vs Xray or Gamma-ray radiation). Equivalent dose is the
absorbed dose multiplied by a weighting factor
Effective dose: Accounts for varying sensitivity of tissues
and organs to radiation. Effective dose is the sum of the
equivalent doses to each tissue and organ exposed multiplied
by tissue weighting factors, measured in seiverts (Sv =
J/kg)
Ionizing Radiation

Radiation Dose
Range of effective doses for diagnostic imaging
procedures ranges from 0.02 mSv for simple
conventional X-rays to 200 mSv for certain
angiography procedures
 Much effort has been placed in determining the
minimal dose amounts required to maintain image
quality and diagnostic ability
 Improving methods for X-ray detection and
amplification, along with digital image manipulation
hold promise for greater reductions in radiation
exposure

Ionizing
1
Radiation
Dose in mGy or mSv
Conventional X-rays
0.02-10
Conventional
Complex X-rays
3-10
CT
5-15
Spiral CT
10-20
Angiography
10-200
Interventional
10-300
Nuclear imaging
3-14
Annual background radiation
2.4mSv
1. Health Risks From Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2 2006.
Ionizing Radiation

Radiation Carcinogenesis
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Believed most frequently to result from activation of protooncogenes or inactivation of tumor suppressor genes via
aforementioned mechanisms
Most epidemiologic data is from high dose exposures,
including atomic bomb survivors, occupational exposures,
and therapeutic irradiation with extrapolation of risk for low
dose exposure
A “stochastic effect”, linear model with no dose threshold is
used for estimating risk of low dose exposures
Determining incidence of carcinogenesis is complicated by a
long latency period, with some solid cancers manifesting 60
years after exposure
Increasing cancer incidence with earlier age at exposure
Ionizing Radiation

Radiation Carcinogenesis
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Estimates for cancer risk:
 Putman’s Textbook of Diagnostic Imaging: 10-5 risk of
new cancer per mGy; or, 1 in 100,000 chance of
new cancer per mGy
 BEIR VII: 2270 total excess cancers and 1140
excess deaths per 100,000 persons exposed to
0.1Gy (100mGy); or, approximately 1 in 400
chance of new cancer and 1 in 800 chance of
death if exposed to 100mGy
Ionizing
1
Radiation
Linear No Threshold High Dose Rate
Linear Model With A Threshold
Linear Quadratic Model
Linear No Threshold Low Dose Rate Model
• Linear no threshold model used for solid cancers
• Linear quadratic better fits risk model for leukemia
1. Health Risks From Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2 2006.
Ionizing
1
Radiation
Solid Cancers
Leukemia
Males
Females
Males
Females
Total
Excess cases per 105
persons exposed to
0.1Gy
800
1300
100
70
2270
Baseline number of
cases
45,500
36,900
830
590
Excess deaths per
105 persons exposed
to 0.1Gy
410
610
70
50
Baseline number of
deaths
22,100
17,500
710
530
1. Health Risks From Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2 2006.
1140
Ionizing
1
Radiation
• It can be seen from this table, examining solid cancer incidence and mortality for
men and women at different ages of exposure, that there is an increased incidence
of solid cancer with earlier age at exposure
1. Health Risks From Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2 2006.
Ionizing Radiation1
• This table illustrates the lifetime attributable risk for specific solid tumors among
105 persons after exposure to 0.1 Gy. Colon and lung cancer occur with greatest
frequency in men compared with breast and lung cancer in women
1. Health Risks From Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2 2006.
Ionizing
1
Radiation
• Unlike solid cancers, there does not appear to be a strong association between
increased incidence of leukemia with earlier age at exposure
1. Health Risks From Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2 2006.
Ionizing Radiation
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Hereditary Effects of Radiation
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Germline mutations
may lead to hereditary disorders in the progeny of
irradiated persons
 The risk is exceedingly low with diagnostic imaging
and estimates are only indirectly available, rely heavily
on mouse models, and pertain to continued low dose
radiation exposure with risk calculated for dosing intervals
of 1 Gy
 Overall, the predicted risk per 1 Gy represents only
0.4-0.6% of baseline frequency of Mendelian,
Chromosomal, and Multifactorial diseases in first
generation progeny

Ionizing
1
Radiation
• This table shows there is an estimated increase of ~3000-4700 Mendelian,
chromosomal, and multifactorial diseases within the first generation per Gy
per million progeny with continued low dose exposure
1. Health Risks From Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2 2006.
Ionizing Radiation

Hereditary Effects of Radiation
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Infertility (occurring with gonadal irradiation)
Risk of permanent sterility exceedingly low with
doses used for diagnostic imaging
 Males: 0.15 Gy may cause oligospermia, 0.5 Gy may cause
azoospermia and temporary sterility, 6 Gy or more may
cause permanent sterility
 Females: age dependent, may result in significant hormonal
changes, 12 Gy in pre-pubertal and 2 Gy pre-menopausal
may cause permanent sterility
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Ionizing Radiation
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Effects of Radiation on the Embryo and Fetus
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Fetus particularly susceptible to effects of radiation due to
rapid cellular growth with critical developmental stages
Effects dependent on dose and gestational age at exposure
and include intra-uterine death, congenital malformations,
growth retardation, mental retardation, and cancer
Association between x-ray exposure in utero and childhood
malignancy exists, some reviews citing a 40% increase in
relative risk following obstetric X-ray, with an excess absolute
risk of about 6% per Gy
Recommended maximum monthly permissible dose to a
fetus is 0.5 mSv
Dose of 0.1 Gy (100 mGy) between 10 days and 25 weeks
gestation is often regarded as cutoff point above which
therapeutic abortion is considered
Ionizing Radiation
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Miscellaneous Factoids
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Questions?
Contrast Media
Contrast
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1
Media
Utilizing radiodense substances to help identify normal
anatomic structures such as bowel wall and vasculature
as well as pathologic conditions such as cancer and
hemorrhage.
Types of contrast media:
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Barium Sulfate agents
Water-Soluble agents
Oil-based agents
Paramagnetic (Gadolinium) agents (for use in MRI)
Micro-bubble based agents (for use in ultrasound)
1. From Daffner’s Clinical Radiology: The Essentials, Second Edition 1999
Contrast Media
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Epidemiology of Adverse Reactions to Contrast:
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Society of Radiology (n=150,000):
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Overall incidence 5%
Severe reactions 1:1000-2000, death 1:13000-40000
2x risk with history of allergy
3x risk with history of previous adverse reaction to contrast
Pre-testing and anti-histamine/steroid pre-treatment of no
benefit
Japan/Australia Study (n=337,647)
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Overall incidence with ionic contrast 12.7%
Incidence with low osmolar/non-ionic 3.1%
Serious reactions 0.22% (ionic) and 0.04% (low osmolar)
Recommend use of low osmolar agents when possible
Contrast Media
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Characterization of adverse contrast reactions:
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Typically mild and may affect CV, Respiratory, Dermatologic,
GI, Nervous, and Urinary systems.
Mild (observation only):
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Intermediate (require treatment, eg benadryl/epinephrine):
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Nausea, vomiting, sneezing, flushing, diaphoresis, warmth, headache
Urticaria, angioneurotic edema, wheezing
Severe (emergent treatment, eg ABC’s, CPR):
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Cardiovascular collapse, pulmonary edema, laryngeal edema, CNS
depression, apnea, death
Contrast Media
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Barium Sulfate:
Finely pulverized barium mixed with dispersing
agents in water
 Oral/rectal administration for outlining GI tract
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Oral for obstruction proximal to ileocecal valve, rectal for
obstruction distal to ileocecal valve: water absorbed by
colon may thicken barium contrast and exacerbate
colonic obstruction if given proximally (orally)
Contraindicated if perforation suspected: causes
severe desmoplastic reaction outside of GI tract
resulting in granuloma and adhesion formation
Contrast Media
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Water-soluble:
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Triiodobenzoic acid common chemical structure
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Ionic: sodium or meglumine salts of diatrizoic or iothalamic acid
Ionic dimers: Linked triiodobenzoic molecules with only one sodium or
meglumine cation
Non-ionic monomers: replaced sodium or meglumine cation with nondissociable side-chain
CT, angiography, GI with suspected perforation, urography,
arthrography, myelography, sinusography
Hypertonic (ionic>ionic dimer>non-ionic) with shift of fluid
to intravascular or intraluminal compartments
Severity of side effects dependent on agent tonicity/viscocity,
amount and rate of infusion, and patient susceptibility (eg
dehydrated, renal or cardiac dysfunction)
Contrast Media
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Water-soluble agent adverse
effects:
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Renal failure
Bradycardia
Decreased BP
Decreased CO
Bleeding from platelet
aggregation abnormalities
Chemical pneumonitis if
aspirated
Headache and Psych
disturbance in myelography
“Hypersensitivity” reaction
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Preventative measures
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Adequate hydration (eg
intravenous fluid administration
pre and post contrast) reduces risk
of adverse reactions (eg renal
failure)
Use of N-acetyl cysteine can
have reno-protective effects
Low osmolality agents have
significantly reduced incidence of
serious adverse reactions but are
more costly
Oil-based or Barium agents may
be used in cases of suspected
esophagotracheal fistula to prevent
chemical pneumonitis
MRI
1
MRI
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Exposes the patient to an intense static magnetic field, a time variant magnetic field,
and pulsed radiofrequency waves, and measures radiofrequency signals generated by
nuclei with odd numbers of protons and neutrons (eg Hydrogen) that possess inherent
magnetic dipoles to create tissue images
Some effects observed from large exposures include thermal effects, physiologic
electric current generation, and ion conduction abnormalities, which may disrupt cell
membranes, alter nerve conduction and CNS function, or cause electrophysiologic
abnormalities such as EKG changes
Levels utilized currently are so low that significant effects are unlikely
Potential consequences from overheating or electric current generation does
exist and has been observed for patients with pacemakers or other metallic
implants or foreign bodies such as clips, prostheses, and metal shavings, with
greatest concern for possible induction of cardiac arrhythmias
Anecdotes of headache, malaise, difficulty in concentration, sleep disturbance, EEG
changes, metabolic/hematologic/immunologic changes have been reported with little
substantiating evidence
MRI procedures often causes patient anxiety due to confinement and length of
procedure, at times managed with benzodiazepine use--be cautious of psychological
and pharmacologic reactions
1. From Putman’s Textbook of Diagnostic Imaging, Second Edition 1994.
Ultrasound
1
Ultrasound
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Acoustic wave form of energy that delineates structures of
different acoustic impedance by detecting sound waves reflected
from the interface of these structures
Carcinogenic, mutagenic, and teratogenic effects are zero
or so low as to not be of concern in medical imaging
Damage can be thermal due to ultrasonic heating from wave
absorption; and, non-thermal due to mechanical effects such as
peak pressure areas, shock waves, and shear stresses at the
interface of micro-cavitation bubbles
Experimentally produced damage in vitro and in vivo using
animal models includes cell lysis, inactivation, altered growth,
altered structure, modified synthetic pathways, and membrane
instability, BUT mostly at intensity levels 10 to 1000 times
greater than that used for diagnostic imaging
1. From Putman’s Textbook of Diagnostic Imaging, Second Edition 1994.
Summation
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Imaging has a pivotal and expanding role in patient care
Risks of ionizing radiation and contrast media are
relatively few and rare at the levels of exposure in
diagnostic imaging, but must not be ignored
Remember first to do no harm—consider need for
imaging and utilize the most appropriate studies to
obtain desired information while minimizing risks
Appropriateness guidelines for imaging may be found
at www.acr.org
The BEIR VII report on risks of low ionizing radiation
may be viewed free online at www.nap.edu
References
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Charles E Putman, Carl E Ravin. Textbook of Diagnostic
Imaging, Second Edition. WB Saunders Company; Philadelphia
1994.
Eric J Hall, Amato J Giaccia. Radiobiology for the Radiologist,
Sixth Edition. Lippincott Williams and Wilkins; New York 2006.
Health Risks From Exposure to Low Levels of Ionizing
Radiation: BEIR VII Phase 2. The National Academies Press;
New York 2006. (available online at www.nap.edu)
Luis Felipe Fajardo L-G, Morgan Berthrong, Robert E
Anderson. Radiation Pathology. Oxford University Press; New
York 2001.
Richard H Daffner. Clinical Radiology: The Essentials, Second
Edition. Lippincott Williams and Wilkins; Baltimore 1999.
All picture images acquired from Google images and Wikipedia.
Meadow the Maggot-Head Says
“Thank You”