RDIOPHARMACY
Diagnostic Nuclear Medicine
Nuclear Medicine
is the branch of medicine concerned with the
use of radionuclides in the study and the
diagnosis of diseases.
•The radionuclides are used for:
1–the assessment of organ function,
2–the detection of disease,
3–the treatment of some diseases and
4–the monitoring of the effects of treatment
The importance of Nuclear Medicine
•It provides:
1–physiological information not available from other
imaging modalities
2–diagnostic information of pathological processes
before the outset of structural changes in an organ
•It uses very small amounts of radioactive
material (radiopharmaceutical) that is introduced
into the body and acts as a tracer
Information obtained using nuclear medicine
techniques is more comprehensive than other
imaging procedures because it demonstrates
organ function not just structure
•The result is that many diseases and cancers
may be diagnosed much earlier
Nuclear medicine vs. other modality
– γ rays are used for imaging
– β rays are used for therapy in nuclear medicine
– Nuclear medicine shows the functions of the organs
and less anatomic information
– Computed tomography, magnetic resonance, ultra
sonography and plain films show the anatomy of the
organs and less of the functions
What is radiopharmacy?
It is a science which deals with the preparation and
dispensing of radiopharmaceuticals(RFs) (radiolabel
drugs)
What are RFs?
Rfs are radiolabel drugs that are used for diagnosis
and treatment
Characteristics of RPs
•The mass amount administered is low
•No intrinsic pharmacological effect
•For diagnostic use
–No disturb physiologic parameter
•For therapeutic use
–Radiation produced the desired therapy
Tow kinds of RPs
1-Diagnostic RPs
2-Therapeutic RPS
Diagnostic RPs
Physical properties
•For physical properties of the radionuclide must be
considered:
1.Physical half life
2.Decay mode
3.Emitted photon energies
4.Availability
Physical properties
Physical half life
•The half life is the time required to reach ½of undecayed
atoms at 0 time
(Tc-99m 6 hours, I-131 8 day)
•Too-long lived RF: unnecessary body irradiation occurs
Physical properties
Photon energy
•The sensitivity and the resolution of the gamma camera
system depends on photon energy
•The energy must be high enough that it escapes the
body without being attenuated and must be also low
enough to be detected by the crystal
•The gamma camera electronics detect radiation in the
60-400keV
•The ideal energy should be in the range of 100-200keV
Physical properties
Decay mode
•Imaging procedures require an electromagnetic
photon (x or γ ray)
•The emitted photon must be high abundance and be
monoenergetic
•β and α rays are not detected
•For diagnostic use a pure γ emitting decay mode
would be desirable
Physical properties
Availability
•The most readily available radionuclide is Tc-99m
pertechnetate
•Tc-99m is eluted from a Mo-99/Tc-99m generator
•The parent Mo-99m decays with a half life of 66 hours
resulting in a shorter lived (6 hours) daughter (Tc-99m)
•A new generator is purchased once a week and supplies
all the Tc-99m needed for that week
Radiopharmacy
Biological properties
•The ideal RP should do the following
–Localize rapidly and exclusively in the organ of interest
–Localize more in pathologic tissue
–Be metabolically and pharmacologically inert
–Have no side effects
–Clear rapidly from background tissue
–Be rapidly excreted after the study is completed
Biological properties
Mechanism of localization
•Functional:
–Passive transfer (diffusion) Tc-99m DTPA
–Active transport or uptake (I-131 in thyroid
–Metabolic trapping (F-18FDG)
–Receptor binding (In-111 pentetreotide)
–Antibody binding (Tc-99m arcitumomab)
Biological properties
Mechanism of localization
•Mechanical
–Capillary blockage (Tc-99m MAA)
–Phagocytosis(Tc-99m sulfur colloid)
–Sequestration (heat denatured Tc-99m RBCsfor spleen
–Compartmental space localization (In-111 DTPA for
CSF flow
–Abnormal extravasations (Tc-99m IDA in bile leaks)
Biological properties
Route of administration
•The route of administration often determine the
localization characteristic of RFs
– IV is the main route
--Lung ventilation can be studied by inhalation of an
aerosol or gas
–Different biodistributions and kinetics can be obtain by
selecting the route of administration
Biological properties
Target uptake
•The RF with a better uptake is a superior imaging agent
(target to nontarget ratio)
•The rate of uptake is also important
–The thyroid can be imaged at 20 min with Tc-99m
pertechnetate , but 4-6 hours with I-123 NaI
Biological properties
RF excretion
•The RF must clear from blood and background tissue to
achieve high contrast
•The major excretion routes are
–Kidneys (glomerular filtrations)
–GI tract
–Hepatobiliary route
Chemical properties
•Ease of preparation and availability
•Tc-99m-based RFs from ready to use commercial
reagent kits
•Stability and expiration
–The best Tc-99m kit formulation give products that are
stable at least 6 hours after preparation
•Stabilized bone scan kits are preferable to non-stabilized
kits
Thank you and Good Luck
Prof. Dr. Omar Shebl Zahra
SKELETAL IMAGING
Bone Scan(Scintigraphy)
Bone scan: A technique to create images of bones on a
computer screen or on film. A small amount of radioactive
material is injected and travels through the bloodstream. It
collects in the bones, especially in abnormal areas of the
bones, and is detected by Gamma Camera.
Bone scans are used for the detection and monitoring of
disorders affecting the bones, including cancer, infections,
and fractures. Bone scanning is also helpful in evaluating
joint diseases.
A bone scan is a test used to detect areas of the bones that are
undergoing rapid turnover due to damage to the bone or new bone
formation.
Skeletal - imaging agents
Overview
Tc-99m labelled bone agents are useful in the detection of bone
lesions that are associated with high metabolic activity such as
tumours, metabolic disorders, and infections of the bone.
The imaging advantages of Tc-99m, coupled with the sensitivity of
bone agent localization in skeletal bone hydroxyapatite matrix,
allows for detection of bone pathology before evidence is shown
by conventional x- rays.
Tc-99m bone agents.
There are many different forms of Tc-99m bone agents, with minor
differences in their individual chemical structure.
Currently used bone-imaging agents are based on either the
P—C—P diphosphonate structure, including Tc-99m medronate
disodium (MDP) and Tc-99m oxidronate.
Or (in the past) the inorganic P—O—P phosphate structure, such
as Tc-99m pyrophosphate.
These bone agents exist as:
sterile ,pyrogen free radiopharmaceuticals ready for IV injection
after reconstitution (labelling) with Tc-99m pertechnetate.
-.
Technetium Tc 99m Medronate (MDP)
Physical properties
(1) All of the Tc-99m bone- imaging agents are susceptible to radiological
decomposition with re-oxidation of the Tc-99m to a higher valence state.
These agents sometimes include antioxidants (e.g. , ascorbic acid) in their
formulation to improve their in vitro stability.
(2) They should be stored at room temperature before and after
reconstitution.
Bio-distribution
It is believed that the localization of the diphosphonates occurs by
chemisorptions onto the hydroxyapatite mineral matrix of skeletal bone with
uptake related to bone metabolic activity and bone blood flow.
Administration and dosage IV, 20 mCi (740 MBq)
CLINICAL PHARMACOLOGY
During the initial 24 hours following intravenous injection of
technetium Tc-99m medronate, about 50 percent of the dose is
retained in the skeleton, and about 50 percent is excreted in the
urine.
A minimum amount of uptake has been observed in soft-tissue
organs, most notably the kidneys. Clearance of radioactivity
from the blood is quite rapid, with about 10 percent of the
injected dose remaining at one hour, and less than 5 and 2
percent at two and four hours, respectively.
The rapid blood clearance (T 1/2 38 to 75 minutes) provides
bone to non-osseous tissue ratios(target to non target ratio)
favouring early imaging.
Following intravenous administration of Tc- 99m MDP , skeletal
uptake occurs as a function of blood flow to bone and bone
efficiency in extracting the complex.
Deposition of radioactivity in bone is rapid and appears to be
related to osteogenic activity as well as the afore mentioned
skeletal blood perfusion , skeletal uptake is bilaterally uniform,
with larger concentrations in the axial structure and in the long
bones.
Increased accumulation of radioactivity may be seen, generally, in
any bone disease state in which there is increased oestrogenic
activity or a localized increase in osseous blood perfusion.
Adverse Reactions
Adverse reactions have not been reported that are specifically
attributable to the use of technetium (99mTc) MDP.
This is also noted with most radiopharmaceuticals used in
nuclear medicine studies.
Allergic dermatological manifestations (erythema) have been
infrequently reported with other similar agents.
Radiation Dosimetry
The effective half-life was assumed to be the physical half-life for all calculated
values. The estimated radiation absorbed doses to an average patient (70 kg)
from an intravenous injection of a maximum dose of 740 MBq (20 mCi) of
technetium Tc 99m MDP.
How to calculate dosage based on body weight?
We never use pounds in medicine - it's always kilograms.
The first thing you need to do is convert the patient's weight from
pounds to kg. (Divide by 2.2)
Then you multiply the dose (given in dose per kg) by the weight in kg.
Example: Pt weighs 154 pounds.
Divide by 2.2 = 70 kg
Dose of 2.5 mg/kg: 2.5 x 70 = 175 mg
Dose Calculation in Nuclear Medicine
Adult dose are designed for 70 kg body weight
Pediatric dose = adult dose x body weight in kg / 70
Thank you and Good Luck
Prof. Dr. Omar Shebl Zahra