nuclear medicine in denr

1. A lecture submitted for
2nd term of Oral Radiology Masters
Cairo University Oral & Dental Medicine College

3.  The use of small amounts of radioactive
materials to diagnose and treat disease.
 Nuclear Medicine shows physiology
whereas Radiology shows anatomy.

4.  Nuclear medicine is a branch or
specialty of medicine and medical
imaging that uses radionuclides and
relies on the process of radioactive
decay in the diagnosis and treatment of
disease.
 The principle of nuclear medicine can be
simplified into a procedure which detects and
produces an image of quantity as well as
distribution of radioactivity of the injected
isotope in a particular tissue studied.

5.  Areas where a dental care provider may utilize
diagnostic isotopes include head and neck tumors,
salivary gland disease, and various metabolic and
infectious processes of the head and neck region.
 Computed tomography (CT) and magnetic resonance
imaging (MRI) with, and without, contrast
enhancement can provide high quality static images
of the soft and hard tissue under study. However,
these imaging modalities provide little physiologic
information about a disease process. On the other
hand, nuclear medicine scans have the ability to
dynamically detect abnormalities at an earlier stage,
well before morphological changes are evident.

6.  The diagnostic modalities of nuclear medicine in oral
and dental practice should be increasingly considered
and an increased awareness in dental surgeons is
needed.
 Its application in diagnostic as well as therapeutic
fields of oral/maxillofacial pathologies needs
discussion and emphasis.

7.  Alpha particles (α):
 Beta particles (β-):
 Positrons (β+):
 Gamma rays:
 X-rays:

8. 1) Labeled molecules and compounds, which
behave virtually identically to the unlabelled ones in
the various chemical, biochemical and biological
processes .
2) Radioactive isotopes form compounds in the same
way like as the stable isotopes .
3) Isotopes disclose their presence by their radiation,
and thus their movement and fate can be traced.
4) For these purposes are used radionuclides that emit
electromagnetic waves (g rays) but don’t emit any
particle (a, b or neutron).

9. 1-Radionuclides or Radioisotopes
2- Gamma camera

10.  Most medical radionuclides are artificially prepared,
They are produced by 3 methods:
 a-Bombardment of stable element with charged beam
(That convert stable nucleus into unstable
(radioactive one).
 b- Irradiation of stable element with neutrons in a
nuclear reactor.
 c- Generator production.

11. 
 Radioisotopes are substances, which contain atomic nuclei
that emit alpha, beta and gamma radiation. If any of these
substances are taken into our body they emit radiation
when they decay giving us a method of locating where it is
present in our body.
 The most often used radio-nuclides are Tc-99m in 'single
photon' imaging and F-18 in 'positron' imaging.
 The selected radioisotope is attached to a convenient
chemical compound that is administered to the
body(mostly intravenous). It then makes its way through
the system leaving a trail of radiation permitting us to trace
its path.

12.  Radionuclides or Radioisotopes+chemical
compound=labeled Radiopharmaceutical.
 Uptake depends on cellular no. or physiology and not
physical changes
 In order to investigate a body organ, a suitable
radioactive tracer having a particular affinity for that
organ is injected into the blood stream this is up taken
by the organ of interest, which is then assessed by
imaging with the gamma camera(distribution in the
body reflects a particular body function or
metabolism)

13.  Half-life: the time taken for a given activity to
reach half its initial value.
 If the radionuclide has a long half-life, the patient and
others would be subjected to a continuous radiation
dose.
 A short half life such as the six hour half life of
technetium 99m, limits the radiation dose, but can
give problems of the time required to transport the
radio nuclide from the production site to the hospital.

17.  Technetium-99m have a physical short half-life of six hours,
140keV (kiloelectron volt)gamma energy, and the radionuclide-
labeled tracers are used in quantities whose emitted radiation
doses are far below the amounts that are toxic to human cells.
 Tc-99m decays to Tc-99 by emitting a gamma ray.
 Technetium 99m: where m means metastable: become stable by
emitting gamma rays .
 80-200 keV is ideal range for gamma camera since higher
will not be absorbed by crystals(NaI)(Ti)and lower will be
absorbed by tissue.
 The competitive adsorption of technetium- 99m labeled
diphosphonates to pure hydroxyapatiteis forty times greater than to
pure organic bone matrix. Thus, its uptake correlates well with the rate
of mineralization.

18.  “Hot spots ”, where the tracer accumulates in greater
amounts than normal, can indicate (a tumor, areas of
increased bone metabolism, Infection increases the
blood supply).
 "Cold" spots have no accumulation of the tracer or
very little. These may point to (cysts, abscesses, or
blood clots, metabolically inactive bone, lack of
osteogenesis, or an absent vascular supply).
 Time needed for procedure to be completed:
From several seconds to several days for the
radiotracer to travel through your body and
accumulate in the organ or area being studied
(depending on the type of exam).

19.  Immediately
 A few hours later
 Or even several days after pt received the radioactive
material.
 Fate of radiotracer
 The small amount of radiotracer in the body will lose its
radioactivity over time.
 It circulates through the bloodstream until they are
either incorporated into sites of active bone turnover or
are excreted in the urine.

21.  It may be
 Suspended over the examination table
 or it may be beneath the table.
 Or dual-headed
 Some cameras can rotate around the body
and produce more detailed images (SPECT).
 Gamma camera capable of recording
dynamic as well as static images of the area
of interest in the patient

22.  Collimator
 Detector crystals (sodium iodide)
 Photomultiplier tube
 Pre amplifier
 Amplifier
 Pulsed height analyser(PHA)
 X-Y positioning circuit
 Display or recording device
 Detector head


23.  Involves a computed scintillation camera that records
the gamma rays emitted by the patient. The camera
has a scintillation crystal that fluoresces at the time of
interaction with the gamma rays. This fluorescence is
detected by photomultiplier tubes, which transform
the flashes of light into electronic signals to produce
an image that is displayed on a computer monitor.

25.  Early detection of lesions(nuclear medicine scans are more
sensitive than other techniques)
 Visualize the structure and function of an organ, tissue, bone or
system of the body. E.g. a-analyze kidney function , b-measure
thyroid function to detect an overactive or underactive thyroid
 Whole body scanning is possible e.g. assessing diseases of the
skeleton and detects tumours when their site is unknown.
 Monitors behaviour following treatment especially drug induced
changes.
 Treatment in some diseases (treating cancer. Tumours are
destroyed by shooting gamma rays at tumours)
 Nuclear medicine therapies include: Radioactive iodine (I-131)
therapy used to treat hyperthyroidism (overactive thyroid gland,
for example, Graves' disease) and thyroid cancer .

26.  Not diagnostic (doesn’t specify diseases but give range
of diseases).
 Generally poor resolution compared with other
imaging modalities
 Radiation risks due to administered radionuclide
 Can be invasive, usually requiring an injection into the
blood stream.
 Relatively high costs associated with radio tracer
production and administration
 time-consuming(imaging may take up to several hours
to perform)

27.  Nuclear medicine is not safe for the use of human beings, so
therefore should not be used on healthy people.
 Also the procedure is not recommended for pregnant women
because unborn babies have a greater sensitivity to radiation
than children or adults.
 So Women should inform their physician if there is any
possibility of being pregnant or if they are breastfeeding .
 The main reason why radioactive sources are used even though
they are dangerous is because the patient is already under risk as
they are ill, so using the radioactive substances would not put the
patient under any further danger but may find a cure for the
illness.
 Radioactive substances are emitted in to the body so the safest
way is to use a radio nuclide which has a short half life, so it can
decay to a safe level in the fastest possible time.

28.  Most of the administered radioactive isotopes is excreted as
urine via the kidney and bladder but same is excreted as
perspiration and saliva. This means that the patient has radio
active substances on their skin and should take extra care when
around other people. If accidents like urination and vomiting
happen, it must be assumed until proven otherwise, that the
contamination is radioactive.
 Pt should inform about any medications, vitamins and herbal
supplements, allergies ,recent illnesses or other medical
conditions.
 In addition to conventional gamma scintigraphic imaging, the
two major nuclear imaging techniques developed are Positron
Emission Tomography (PET) and Single Photon Emission
Computed Tomography (SCECT). Both imaging modalities are
now standard in the major nuclear medicine services.

29.  The amount of radiation from diagnostic nuclear
medicine procedures is kept within a safe limit and
follows the "ALARA" (As Low As Reasonably
Achievable) principle. The radiation dose from nuclear
medicine imaging varies greatly depending on the type
of study. The effective radiation dose can be lower than
or comparable to the annual background radiation
dose. It can also be in the range or higher than the
radiation dose from an abdomen/pelvis CT scan.

37. 1

38.  one of the most commonly performed diagnostic
procedures.
 It uses technetium 99 m methylene disphosphonate, (with
a half-life of 6 hours and a total radiation dose of 0.3
rads. )which taken in bony areas of high metabolic
osteoblastic activity or vascularity. Normal bone should be
symmetrical from midline and demonstrate uniform
radioisotope uptake.
 It is important to keep in mind a bone scan can detect 10-
15% mineral loss, while standard radiographs will only
visualize a bony defect after 35-50% mineral loss. Overall
the scan has a high sensitivity but low specificity.

40.  To diagnose and differentiate osteomyelitis from
cellulitis.
 Detect primary and metastatic malignant disease.
 To assess the vascularity of bone grafts.
 Contribute to the diagnosis of various metabolic bone
diseases such as fibrous dysplasia, Paget’s disease,
osteoarthritis, and rheumatoid arthritis (RA).

41.  A normal bone scan should demonstrate
symmetry around the midline with uniform
uptake of the radiopharmaceutical. There is
usually increased activity at joint margins and
vertebral bodies. Uptake is typically visualized
in the kidneys and bladder.

42.  A three-phase bone scan is often performed to obtain additional
diagnostic information, especially when the clinician is trying to
distinguish osteomyelitis from cellulitis. The three phases
include:
 The dynamic vascular flow phase, where imaging is performed every 2-3
seconds for the first 30 seconds. In this phase, each side can be compared
and differences in vascularity can be seen.
 The blood pool image at five minutes, where the radiopharmaceutical is
mostly in the vascular compartment but is starting to appear in bone.
This phase demonstrates regional differences in blood flow and vascular
permeability.
 Two to four hours later, the osseous delayed static image is obtained
usually for the entire body demonstrating regional distribution in the
skeleton. This phase reflects the metabolic activity of the bone in
question. In non-inflammatory conditions, the third phase is usually the
only image obtained.
 Occasionally, a fourth phase study is performed 24 hours later when
there may be improved contrast between normal bone and inflammatory
conditions.

44.  Static acquisition with a detector in a fixed position relative the patient: examination of
thyroid, kidney....
 Standard bone scans involve the acquisition of static images three hours after tracer
administration. Delayed static images may be useful in the evaluation of benign
conditions, such as condylarhyperplasia. The detector move simultaneously and scan the
patient's body from head to foot.(eg bone scan)
 Three-phase bone scan comprises a flow assessment, a blood pool image, and delayed
static views acquisition, which are frequently performed to evaluate trauma,
inflammatory disease, and primary bone tumors.Three hours after radiotracer
administration, the bony uptake of technetium-99m labeled diphosphonates is maximal,
andsignificant proportion of the unbound tracer will be excreted by the kidneys.
Therefore, the final delayed static images are acquired at this time.
 Tomographic acquisition: The Positron Emission Single Photon (SPECT): detectors
rotate around the patient to obtain in a digital representation of a 3D radioactive
distribution of the body: chest, pelvis, skull....
 The dynamic flow study requires rapid sequential images for sixty seconds during the
intravenous administration of the radiotracer. This is followed by a blood pool image
reflecting tissue hyperemia and is acquired immediately after the flow study( kidney and
bone phase’s vascular scans).

45.  Bone scans can also use Single Photon Emission
Computed Tomography (SPECT) technology
where tomographic images obtained in three
planes (axial, coronal, and sagittal) allows a more
accurate interpretation and better localization of
bone pathology. SPECT images are obtained from
different angles and then reconstructed by a
computer. SPECT can be used for evaluation of,
with sensitivity equal to that of a MRI for bone
pathology.

46.  SPECT imaging method is equivalent in scintigraphy to
Computed Tomography (CT) in radiology. The injected
radioactive tracers emit during their disintegration gamma
photons which are detected by an external detector, after
passing through the surrounding tissue.
 In SPECT, the main radioactive isotopes are technetium-
99m, Iodine and Thallium-201
 It is accomplished by Using rotating camera
 it is able to provide true 3D information. This information
is typically presented as cross-sectional slices through the
patient and can be freely reformatted or manipulated as
required.

47.  N.B SPECT studies acquir rotating delayed static
images, generally sixty-four projections over 360º,
followed by computer reconstruction to provide three
dimensional multiplanar slices in the axial, coronal,
and sagittal planes, relative to the patient’s body.
(e.g.)temporomandibular joints’ internal derangement
could be investigated by means of SPECT images.

49.  Collimator
 The collimator is an important component in a SPECT machine.it include:
 Two-dimensional parallel channels were The first collimators used (Figure a). By rotating the
detector & collimator assembly around the patient, two-dimensional projections are obtained, and
the distribution of radioactivity may be 3D reconstructed slice by slice. These parallel collimators are
used in the vast majority of SPECT systems used in Nuclear Medicine services. The resolution of these
systems varied from 10 to 15 mm.
 converging channels collimators were developed (Figure b).To increase the sensitivity and
resolution of SPECT systems, The first proposed included a series of converging channels to a focal
line which is parallel to the rotation axis of the system .This system is therefore equivalent to a
scanner used in X-ray fan beam tomography where 3D image is reconstructed slice by slice.

 It is used for imaging small organs such as heart and brain, This allows obtaining magnification of the
object in all directions(cross and longitudinal). This kind of collimators can be used only for small
field tests, so for small structures, the size of the detectors has not increased. With these systems,
image data registration is completely 3D as well as in cone beam X-ray tomography, and therefore
reconstruction is not performed slice by slice.

 Diverging collimator (Figure c) is reserved to large structure imaging.
 Pin-hole collimator (Figure d) allows obtaining a mirror image with a variable magnification
function of collimator depth and object to collimator distance. This collimator is suitable for small
structures imaging such as thyroid and hip.

51.  Camera head or heads revolve about the patient, acquiring projection images from evenly spaced
angles
 May acquire images while moving (continuous acquisition) or may stop at predefined angles to
acquire images (“step and shoot” acquisition)
 Using too few projections creates radial streak artifacts in the reconstructed transverse images
 After projection images are acquired, they are usually corrected for axis-of-rotation misalignments
and for non uniformities
 Following these corrections, transverse image reconstruction is performed using either filtered back
projection ((as in CT) )or iterative methods

 SPECT image processing parameters include also the following:
 1. Filtering: improve image quality by removing noise and blur
 2. Reconstruction: by analytical or iterative methods
 3. Motion correction: recommended to reduce motion blur due to object motion
 4. Attenuation correction: identifying source of attenuation for image correction
 5. Quantification: assessment by image quantification of the affected area
 6. Normal database: reference used for calculation of extent and severity of defect
 7. Segmentation: process of partitioning a digital image into multiple segments to simplify and/or
change the representation of an image into something that is more meaningful and easier to analyze


52.  Gallium 67 citrate, once given intravenously, accumulates non-
specifically in areas of inflammation, infection, and neoplasm having an
affinity for rapidly dividing cells, i.e., WBC and tumor cells. Gallium can
be used in evaluating abscesses, lymphomas, sarcoidosis, and
osteomyelitis.
 Because of Gallium’s long half-life (78 hrs), if a technetium bone (half-
life of 6 hours) scan is being contemplated, it should be performed first.
 No longer a common test. A triple phase bone scan is the
diagnostic test of choice for confirming the diagnosis of osteomyelitis.
However, the triple phase bone scan, while highly sensitive, is non-
specific.
 Gallium imaging may increase the specificity of a positive bone scan,
especially if osteomyelitis is superimposed on another underlying acute
or chronic bone disease.
 The Gallium scan is also useful for monitoring the response to
treatment, with a reduction in Gallium 67 accumulation a good indicator
of a resolving osteomyelitis.

54.  The major salivary glands with a functioning parenchyma have the ability to take up
technetium 99m pertechnetate in sufficient quantities to be imaged, since the Te99 mimics
chloride influx into the acinar cells.
 Scintigraphy of these glands is used for functional evaluation and evaluating mass lesions.
Scintigraphy involves administering a radioactive tracer with an affinity for the organ or
tissue of interest; the distribution of the radioactivity is then recorded with a scintillation
camera.
 Other uses include detecting aplasia or agenesis of the gland, evaluating obstructive
disorders, traumatic lesions, fistulas, or function after surgery.
 By itself, this study is rarely diagnostic but is a useful adjunct.
 Initially, images are obtained five minutes after injection of technetium 99m pertechnetate.
 After ten minutes, the gland is stimulated by a sour drink or candy. Repeat images are then
obtained.
 Mass lesions in a gland usually present as areas of decreased uptake, with the notable
exception of Wharthin’s tumor and oncocytomas which demonstrate increased uptake and
decreased washout time.
 Patients with Sjogren’s Syndrome may have poor uptake of the radiopharmaceutical and poor
response to stimulation.
 Acute inflammation of the glands usually demonstrates increased uptake and increased
washout, whereas chronic inflammation shows decreased uptake.

55. 4

57.  The use of positron emission tomography (PET) metabolic imaging has
increased significantly over the last several years. PET imaging has value
in cardiovascular, neurological, psychiatric, and oncological diagnosis.
 PET is a functional imaging modality that allows the measurement of
metabolic reactions within the whole body. 18F-fluorodeoxyglocose
(FDG) is the radiopharmaceutical most commonly used in PET
scanning. FDG is a glucose analog that is transported into cells and
phosphorylated like glucose, but the metabolism stops at this point and
the phosphorylated FDG becomes trapped in the cell and starts to
accumulate.
 Most tumors, with a more rapid growth rate, have an increased rate of
glucose use due to an increased rate of glycolysis compared to normal
tissue or scar tissue. Consequently, FDG preferentially accumulates in
tumor cells and demonstrates an increased uptake especially in poorly
differentiated tumors. The accumulated FDG is detectable to the PET
camera. To assure adequate uptake of FDG, the patients are required to
fast to prevent hyperglycemia which would confound the result.

58.  There are many clinical uses for PET in head and neck cancer. PET can detect
nodal neck disease in oral squamous cell carcinoma (OSCCA), often at an earlier
stage than CT or MRI which rely on morphological change PET can be used to
assess the response of a tumor to treatment, diagnose recurrence, detect residual
disease, or detect distant unknown metastases. PET scanning is helpful in
evaluating a neck mass or evaluating a neck without palpable adenopathy (staged
as a N0 neck) in oral squamous cell carcinoma. PET is especially useful when
trying to localize an occult primary tumor. PET has not shown any usefulness in
pre-operative evaluation of salivary gland neoplasms.
 In OSCCA, there has been a great deal of interest in using PET to evaluate the
clinically N0 neck for occult or micrometastasis before any changes are visible on
CT or MRI.16 Preliminary studies in this area have been very encouraging. If the
sensitivity and specificity of PET in evaluating nodal neck disease in OSCCA is
found to be clinically acceptable, then many patients will be spared an elective
neck dissection. However, PET can give false positive results. FDG may
accumulate in non-neoplastic tissue such as new granulation tissue, areas of
inflammation, and early post-op scarring. For example, the OSCCA patient with a
recently irradiated neck would likely have a false positive result for two to three
months after the conclusion of radiation treatment. False positives can also occur
in conditions such as tuberculosis and sarcoidosis.
 Overall, while the sensitivity can be lacking, the specificity is high.

59. 5

62.  Lymphoscintigraphy is an exciting technique that is receiving
much clinical research attention in the treatment of oral and
head/neck malignancy, especially OSCCA. Lymphoscintigraphy is
already used routinely in the treatment and staging of breast
cancer and malignant melanoma.
 Briefly, technetium 99m sulfur-colloid is injected in four to six
subcutaneous sites around the neoplastic lesion. The radioactive
colloid will be carried away in the lymphatic channels to the first
echelon lymph node draining that area, the so-called sentinel
node. The sentinel node is felt to be the best predictor of nodal
spread of the tumor. The pattern of lymphatic spread and the
sentinel node can then be imaged using a gamma camera. One to
two hours later, in the operating room, the surgeon using a hand
held gamma counter is able to localize the node and remove it.

63.  The sentinel node is evaluated for metastatic disease. If the sentinel
node is free of disease, it is presumed the remaining nodes in the
regional nodal basin are free of disease. On the other hand, if the
sentinel node is positive for disease, then the remaining nodes are
removed.
 Because of sentinel node mapping, many women with breast cancer
have been spared full axillary nodal dissections and the sequella of
persistent upper extremity lymphadema. The sentinel node is any node
that receives drainage from any given anatomic location. It can be
located in the neck, axillae, groin, or elsewhere in the body. It can
theoretically be in any of the 6 levels of the neck, if it is the primary first
echelon node draining the site of a primary malignancy.
 Currently there are numerous clinical research protocols being
performed at centers across the country where the accuracy of sentinel
node biopsy in the treatment of OSCCA is being evaluated. This again
could play an important role in the management of the N0 neck, where
the sentinel node is removed and evaluated. If the node is disease free,
the patient is spared an elective neck dissection. On the other hand, if
the node is positive, the patient goes on to a more formal neck
dissection.

64. 6

66. 7

68.  References:
 1- Baur DA, Heston TF, Helman JI. Nuclear
Medicine in Oral and Maxillofacial Diagnosis: A
Review for the Practicing Dental Professional. J
Contemp Dent Pract 2004 February ;(5)1:094-104.
 2- INTRODUCTION TO NUCLEAR MEDICINE. Gill
Clarke 2005.
 3- ENGG 167. MEDICAL IMAGING. Nov. 6. Nuclear
Medicine & SPECT imaging. (a lecture from
Internet)