Advanced Biomedical Imaging Dr. Azza Helal Dr. Azza Helal A. Prof. A. Prof. of Medical Physics of Medical Physics Faculty of Medicine Faculty of Medicine Alexandria University Alexandria University Lecture 8 Lecture 8 Isotope scans, Radiation Isotope scans, Radiation unites unites & & Radiation hazards Radiation hazards
Lecture 8 Isotope scans, Radiation unites & Radiation hazards. Advanced Biomedical Imaging. Dr. Azza Helal A. Prof. of Medical Physics Faculty of Medicine Alexandria University. Isotope scans. - PowerPoint PPT Presentation
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Advanced Biomedical Imaging
Dr. Azza HelalDr. Azza HelalA. Prof.A. Prof. of Medical Physics of Medical Physics
Faculty of MedicineFaculty of MedicineAlexandria UniversityAlexandria University
γ decay• γ rays are emitted during any radioactive decay
Isotope T1/2 Decay Isotope T1/2 Decay
Kr81m 13sec IT Tc99m 6hrs IT
Th201 73hr EC Xe133 5days γ & B
I123 13hr EC I131 8days B-
G67 78hr EC F18 110 min B+
TT1/21/2 of different atoms. of different atoms.
Half life time (T1/2 ) is the time required for a given nuclei to decay to ½ of its original value.
Radiopharmaceuticals:
Combination of Radionuclides with chemical
compounds (pharmaceuticals)
Once administered to the patient, it can
localize to specific organs allowing diagnosis
of a disease based on the cellular function
rather than the anatomy.
Radiopharmaceuticals (desirable properties):
Short t1/2 (few hours)
Decay to stable daughter,
Emits γ rays (isomeric transition)
Emits mono-energy γ rays (50-300) (150Kev).
So 99mTc is the best one.
– Radiation exposure is low:
It has a short t1/2 (6hrs)
Emits γ ray allowing small amounts to be detected.
Its quick decay into the less radioactive 99Tc.
Technetium-99m generator (technetium cow)
it is used to extract 99mTc from decaying of 99Mo.
99Mo is used as:
– has a t1/2 of 66 hr
– easily transported to hospitals where it decays to 99mTc (t1/2 6hr, inconvenient for transport).
Mo99 decays to pertechnetate. Pulling normal saline solution through the column of 99Mo elutes the soluble 99mTc, resulting in Na pertechnetate which is then injected to the patient.
After a wk, generator is
replaced.
Uses of Tc99m:
99Mo → 99mTc + β− (in generator)
99mTc → 99Tc + γ (in patient)
Na pertechnetate is used for imaging of tissues as thyroid, gastric mucosa & salivary glands.
it can be labeled to a wide variety of compounds e.g. – HMPAO for cerebral imaging.– HIDA for billiary studies. – MAG3 for renal studies. – DTPA for lung ventilation studies – Diphosphonate for bone imaging.
Precautions FOR handling radionuclides:
Segregation:
separated area for preparation, storage, injection,
patient to wait & image, temporary storage of waste.
patient is considered as a source of external radiation.
Follow inverse square low to decrease the exposure.
The room should be with continuous floor, glass
painted wall and formica topped benches.
Simple mixing with the compound to be labeled at
room temperature, use shielded syringes to transfer.
Personal protection:
Use the three important factors for protection, time, distance & barriers.
Time should be as short as possible (no eat, drink….) Distance from the source should be as long as possible
so use long handle forceps Barriers used as: Lead shielded generators, bottle & syringes Lead glass barriers. Special containers for transport water proof surgical gloves, cover cuts and abrasion,
Patient protection:
Check activity, avoid contamination, deal with the spills, vomiting, incontinence.
if there is contamination:
– Mop the floor with absorbent pads and seal the swabs in plastic bags & continue cleaning and monitor to check that the dose is low.
– If necessary cordon off the area or cover it with
impervious sheet till sufficient decay has occurred.
Disposal of the waste:
Contaminated materials are treated as waste.
Gaseous waste vent to atmosphere, aqueous waste diluted with water via designated sink
solid waste are placed in designated sack for disposal by incineration.
Contaminated cloths and bedding is bagged & stored in a secure protected area until sufficiently decayed.
Dose to the patient: increases in proportion to:
– Activity and the fraction taken up by the
organ.
– Effective t1/2 in the organ.
– not affected by scan time / number of images
Decrease the dose to the patient:
Drinking a lot of water
Empty the bladder to reduce dose to gonads
Avoid contamination
Gamma imaging
While X ray, CT and MRI isolate anatomic changes in the body, gamma imaging is capable of detecting areas of molecular biology detail even prior to anatomic change.
This is by counting the radioactivity and its distribution in the organ.
Isotope scans
Gamma camera components (scintillation counter):Gamma camera components (scintillation counter):
Gantry (collimator,detector crystal & photomultiplier tube in evacuated glass envelope) & data analysis computer.
Gantry is connected to computer & both control operation of the camera, acquisition and storage of images.
Collimator: lead disk with many holes separated by septa to absorb most gamma rays not parallel to collimator..
NAI crystal is connected to 100 photomultiplier
photomultiplier components: photocathode, 10-12 dynodes and anode.
When a gamma ray interacts in the crystal, it produces light which strikes photocathode producing low energy electrons. These electrons are focused and accelerated by the dynodes until about one million reach the anode.
Size of pulse which emerges from anode is α to number of electrons which are ejected from photocathode which is α to amount of light in turn α to energy which was absorbed from gamma-ray photon by the crystal.
A computer is used with gamma camera to electronically process these signals
Gamma Camera Planar ImagingGamma Camera Planar Imaging
single projection viewno image reconstruction is required
Tomography with radionuclideTomography with radionuclide
It includes SPECT (Single Photon Emission CT) & PET (Positron Emission Tomography).
Both rely on similar principles to produce images:
– use of radioactive tracer & detection of gamma rays.– tracer is chemically combined with biologically active
molecule.– waiting period for active molecule to be concentrated in
tissues of interest– then the patient is placed in the imaging scanner.
– During scan a record of tissue concentration is made as tracer decays
Differences between SPECT & PETDifferences between SPECT & PET
SPECT PET
Tracer Na pertechnotate
99mTc )6Hrs(
Flurodeoxyglucose (FDG)Fluorine-18
)110 min(
Production Generator Cyclotron
Detection site Decay Annihilation
Detector crystal One large
NaIMultiple
bismuth germinate
Camera Rotating Stationary
Collimator Present Absent
Detect Blood flow & Metabolic activity
Glucose uptake &Metabolic activity
Resolution Lower Higher
Cost Less High
Single head SPECT
Double head SPECT Triple head SPECT
)PET(
30.000
F18 undergoes positron emission decay. After traveling up to a few mm positron encounters an electron producing a
pair of annihilation photons moving in opposite directions and detected.
PET CT images show metastases to left supraclavicular lymph node a and to liver b
Differences between X-ray Imaging Differences between X-ray Imaging &&
Heart/blood flow 25 (930) 99mTc Red Blood Cells 600 (6.0)
Summary of Recommendations for Radiopharmaceuticals Excreted in the Breast Milk8 Administered
Pharmaceutical Activity, mCi (MBq)
Counseling?* Advisory
67Ga Citrate 5.0 (185) Yes Cessation 99mTc DTPA 20 (740) No 99mTc MAA 4 (148) Yes 12 hr 99mTc Pertechnetate 30 (1,110) Yes 48 hr 131I NaI 150 (5,550) Yes Cessation 51Cr EDTA 0.05 (1.85) No 99mTc IDA agents 8 (300) No 99mTc Glucoheptonate 20 (740) No 99mTc HAM 8 (300) No 99mTc MIBI 30 (1,110) No 99mTc MDP 20 (740) No 99mTc PYP 20 (740) No 99mTc Red Blood Cells in vivo 20 (740) Yes 12 hr 99mTc Red Blood Cells in vitro 20 (740) No 99mTc Sulfur Colloid 12 (444) No 111In White Blood Cells 0.5 (18.5) No 123I NaI 0.4 (14.8) Yes Cessation** 123I OIH 2 (74) No 123I mIBG 10 (370) Yes 48 hr 125I OIH 0.01 (0.37) No 131I OIH 0.3 (11.1) No 99mTc DTPA Aerosol 1 (37) No 99mTc MAG3 10 (370) No 99mTc White Blood Cells 5 (185) Yes 48 hr 201Tl Chloride 3 (111) Yes 96 hr
Nursing mothers must be counseled about the need to interrupt / discontinue breast feedingPumped milk may be refrigerated and used after the radioactivity has decayed
Complete cessation of breast feeding:
Ga-67 citrate
I-131 sodium iodide therapy
Interruption of breast feeding for 12 hours:
Tc-99m macroaggregated albumin
Tc-99m–labeled RBCs (in vivo labeling)
In-111–labeled WBCs
Interruption of breast feeding for 24 hours:
Tc-99m pertechnetate
I-123 metaiodobenzylguanidine
Tc-99m–labeled WBCs
Interruption of breast feeding for 168 hours:
Tl-210 chlorided
Early effects
– Whole body
– Partial body
– gonadalLate effects
Acute radiation syndrome
Teratogenic effects
Effect of radiation on the body
Radiation protectionRadiation protection
Radiation protection
To be sure that the dose received by person is small as possible so that the consequent damage
never constitute a significant hazards to the heath of irradiated person.
Maximum permissible dose (MPD)
The dose which is not expected to cause any detectable body injury for the person during his life time and till his 3rd generation.
Radiation exposures divided into 3 categories:
– Occupational exposure. (2Rem/yr, 20 mSvmSv).
– Medical exposure, (special group), persons work in controlled area (1.5Rem/yr)
– Public exposure 1/10 occupational exposure.
– Pregnant worker 1msv Pregnant worker 1msv
– Dose to embryo 5 mSv = 0.5 rem in 9mthDose to embryo 5 mSv = 0.5 rem in 9mth
Radiation detectors:
• Radiation survey meter
(Geiger Muller counter)
2. Personnel Monitoring
1. Film badge: permanent records, cheap, not accurate, hard processing, over exposure not detected at once
2. TLD : accurate, small, used in in vivo dosimetry, no permanent records, more expensive, over exposure not
detected at once. 3.Pocket dosimeter: over exposure detected at once,
expensive, no permanent records
Personnel Monitoring devices
Radiation Protection & Exposure Control
Time– Reduce the time spent near a radiation source
Distance– Inverse square law
– Radiation intensity is 1/distance 2
– NCRP recommends that personnel should stand at least 2m from x-ray tube and patient and behind a shielded barrier