A bone scan or bone scintigraphy is a
nuclear medicine
Nuclear medicine or nucleology is a medical specialty involving the application of radioactive substances in the diagnosis and treatment of disease. Nuclear imaging, in a sense, is " radiology done inside out" because it records radiation emi ...
imaging technique of the bone. It can help diagnose a number of bone conditions, including
cancer of the bone or
metastasis
Metastasis is a pathogenic agent's spread from an initial or primary site to a different or secondary site within the host's body; the term is typically used when referring to metastasis by a cancerous tumor. The newly pathological sites, then ...
, location of bone
inflammation
Inflammation (from la, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants, and is a protective response involving immune cells, blood vessels, and molec ...
and
fractures (that may not be visible in traditional
X-ray images), and bone infection (osteomyelitis).
Nuclear medicine provides functional imaging and allows visualisation of
bone metabolism or
bone remodeling
Bone remodeling (or bone metabolism) is a lifelong process where mature bone tissue is removed from the skeleton (a process called ''bone resorption'') and new bone tissue is formed (a process called ''ossification'' or ''new bone formation''). ...
, which most other imaging techniques (such as X-ray
computed tomography, CT) cannot. Bone
scintigraphy
Scintigraphy (from Latin ''scintilla'', "spark"), also known as a gamma scan, is a diagnostic test in nuclear medicine, where radioisotopes attached to drugs that travel to a specific organ or tissue (radiopharmaceuticals) are taken internally and ...
competes with
positron emission tomography (PET) for imaging of abnormal metabolism in bones, but is considerably less expensive. Bone scintigraphy has higher
sensitivity but lower specificity than CT or MRI for diagnosis of
scaphoid fracture
A scaphoid fracture is a break of the scaphoid bone in the wrist. Symptoms generally includes pain at the base of the thumb which is worse with use of the hand. The anatomic snuffbox is generally tender and swelling may occur. Complications may ...
s following negative
plain radiography.
History
Some of the earliest investigations into skeletal metabolism were carried out by
George de Hevesy
George Charles de Hevesy (born György Bischitz; hu, Hevesy György Károly; german: Georg Karl von Hevesy; 1 August 1885 – 5 July 1966) was a Hungarian radiochemist and Nobel Prize in Chemistry laureate, recognized in 1943 for his key rol ...
in the 1930s, using
phosphorus-32
Phosphorus-32 (32P) is a radioactive isotope of phosphorus. The nucleus of phosphorus-32 contains 15 protons and 17 neutrons, one more neutron than the most common isotope of phosphorus, phosphorus-31. Phosphorus-32 only exists in small quantiti ...
and by
Charles Pecher in the 1940s.
In the 1950s and 1960s calcium-45 was investigated, but as a
beta emitter
In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which a beta particle (fast energetic electron or positron) is emitted from an atomic nucleus, transforming the original nuclide to an isobar of that nuclide. For exam ...
proved difficult to image. Imaging of
positron and
gamma emitters such as
fluorine-18
Fluorine-18 (18F) is a fluorine radioisotope which is an important source of positrons. It has a mass of 18.0009380(6) u and its half-life is 109.771(20) minutes. It decays by positron emission 96% of the time and electron capture 4% of the time ...
and
isotopes of strontium
The alkaline earth metal strontium (38Sr) has four stable, naturally occurring isotopes: 84Sr (0.56%), 86Sr (9.86%), 87Sr (7.0%) and 88Sr (82.58%). Its standard atomic weight is 87.62(1).
Only 87Sr is radiogenic; it is produced by decay from th ...
with
rectilinear scanners was more useful. Use of
technetium-99m
Technetium-99m (99mTc) is a metastable nuclear isomer of technetium-99 (itself an isotope of technetium), symbolized as 99mTc, that is used in tens of millions of medical diagnostic procedures annually, making it the most commonly used medical ra ...
(
99mTc) labelled
phosphate
In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid .
The phosphate or orthophosphate ion is derived from phosph ...
s,
diphosphonates or similar agents, as in the modern technique, was first proposed in 1971.
Principle
The most common
radiopharmaceutical
Radiopharmaceuticals, or medicinal radiocompounds, are a group of pharmaceutical drugs containing radioactive isotopes. Radiopharmaceuticals can be used as diagnostic and therapeutic agents. Radiopharmaceuticals emit radiation themselves, which ...
for bone scintigraphy is
99mTc with
methylene diphosphonate (MDP). Other bone radiopharmaceuticals include
99mTc with HDP, HMDP and DPD.
MDP
adsorbs onto the crystalline
hydroxyapatite mineral of bone. Mineralisation occurs at
osteoblasts, representing sites of bone growth, where MDP (and other diphosphates) "bind to the hydroxyapatite crystals in proportion to local blood flow and
osteoblastic activity and are therefore markers of bone turnover and bone perfusion".
The more active the
bone turnover, the more radioactive material will be seen. Some
tumor
A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...
s,
fractures and
infection
An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable dis ...
s show up as areas of increased uptake.
Note that the technique depends on the osteoblastic activity during remodelling and repair processes following initial osteolytic activity. This leads to a limitation of the applicability of this imaging technique with diseases not featuring this osteoblastic (reactive) activity, for example with
multiple myeloma. Scintigraphic images remain falsely negative for a long period of time and therefore have only limited diagnostic value. In these cases CT or MRI scans are preferred for diagnosis and staging.
Technique
In a typical bone scan technique, the patient is injected (usually into a vein in the arm or hand, occasionally the foot) with up to 740
MBq
''MBQ'' is an original English-language manga created by Tokyopop's Rising Stars of Manga second-place winner Felipe Smith.
''MBQ'' is an expansion of his second-place winning entry in the third Rising Stars competition. It is the story of a y ...
of
technetium-99m-MDP and then scanned with a
gamma camera
A gamma camera (γ-camera), also called a scintillation camera or Anger camera, is a device used to image gamma radiation emitting radioisotopes, a technique known as scintigraphy. The applications of scintigraphy include early drug development ...
, which captures planar
anterior and posterior or
single photon emission computed tomography
Single-photon emission computed tomography (SPECT, or less commonly, SPET) is a nuclear medicine tomographic imaging technique using gamma rays. It is very similar to conventional nuclear medicine planar imaging using a gamma camera (that is, ...
(SPECT) images.
In order to view small lesions SPECT imaging technique may be preferred over planar scintigraphy.
In a single phase protocol (skeletal imaging alone), which will primarily highlight osteoblasts, images are usually acquired 2–5 hours after the injection (after four hours 50–60% of the activity will be fixed to bones).
A two or three phase protocol utilises additional scans at different points after the injection to obtain additional diagnostic information. A dynamic (i.e. multiple acquired frames) study immediately after the injection captures
perfusion information.
A second phase "blood pool" image following the perfusion (if carried out in a three phase technique) can help to diagnose inflammatory conditions or problems of blood supply.
A typical
effective dose obtained during a bone scan is 6.3
millisieverts (mSv).
File:Woldobonescan.JPG, Person undergoing a bone scan on the skull
File:SPECT CT.JPG, A patient undergoing a SPECT bone scan.
PET bone imaging
Although bone scintigraphy generally refers to gamma camera imaging of
99mTc radiopharmaceuticals, imaging with
positron emission tomography (PET) scanners is also possible, using
fluorine-18
Fluorine-18 (18F) is a fluorine radioisotope which is an important source of positrons. It has a mass of 18.0009380(6) u and its half-life is 109.771(20) minutes. It decays by positron emission 96% of the time and electron capture 4% of the time ...
sodium fluoride
Sodium fluoride (NaF) is an inorganic compound with the formula . It is used in trace amounts in the fluoridation of drinking water, in toothpaste, in metallurgy, and as a flux. It is a colorless or white solid that is readily soluble in water. I ...
(
18F">sup>18FaF).
For
quantitative measurements,
99mTc-MDP has some advantages over
18F">sup>18FaF. MDP renal clearance is not affected by urine flow rate and simplified data analysis can be employed which assumes
steady state
In systems theory, a system or a process is in a steady state if the variables (called state variables) which define the behavior of the system or the process are unchanging in time. In continuous time, this means that for those properties ''p' ...
conditions. It has negligible tracer uptake in
red blood cells, therefore correction for plasma to whole blood ratios is not required unlike
18F">sup>18FaF. However, disadvantages include higher rates of protein binding (from 25% immediately after injection to 70% after 12 hours leading to the measurement of freely available MDP over time), and less
diffusibility due to higher
molecular weight
A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioch ...
than
18F">sup>18FaF, leading to lower
capillary permeability.
There are several advantages of the PET technique, which are common to PET imaging in general, including improved
spatial resolution
In physics and geosciences, the term spatial resolution refers to distance between independent measurements, or the physical dimension that represents a pixel of the image. While in some instruments, like cameras and telescopes, spatial resolut ...
and more developed
attenuation
In physics, attenuation (in some contexts, extinction) is the gradual loss of flux intensity through a medium. For instance, dark glasses attenuate sunlight, lead attenuates X-rays, and water and air attenuate both light and sound at variabl ...
correction techniques. Patient experience is improved as imaging can be started much more quickly following radiopharmaceutical injection (30–45 minutes, compared to 2–3 hours for MDP/HDP).
18F">sup>18FaF PET is hampered by high demand for scanners, and limited tracer availability.
References
External links
*
{{Bone, cartilage, and joint procedures
3D nuclear medical imaging
Medical imaging
Radiology
Scintigraphy