Nuclear Medicine Resources Manual

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CHAPTER 5. GUIDELINES FOR GENERAL IMAGING

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started as early as 1.5 hours after injection when HEDP is used. By

commencing scanning earlier, more photons are yielded per injected amount of

tracer, resulting in an improvement of the system sensitivity. Delayed static

imaging can be reinforced with planar pinhole magnification, conventional

SPECT and pinhole SPECT when necessary (see the following paragraphs).

(d) Planar pinhole bone scintigraphy

Planar pinhole bone scintigraphy is performed using either single head or

dual head gamma camera systems simply replacing a multihole collimator(s)

with a pinhole collimator(s). Pinhole scintigraphy significantly enhances the

resolution through optical magnification. This mode generates either a single

magnified view or a pair of magnified views of a selected portion of the

skeleton in any desired projection. Dual head planar pinhole scintigraphy

eliminates the ‘blind zone’ seen on single head pinhole images and reduces the

scan time by half. Optimal pinhole scintigraphy of a portion of the skeleton

takes 15–20 min using a pinhole with a 4 mm aperture.

(e) Conventional single photon computed tomography of bone

Bone SPECT produces sectional images of a portion of the skeleton. The

standard projections are transverse, coronal and sagittal. SPECT can separate

selected plane or small volumes of tissue from other tissues that overlie or

underlie them, improving the image contrast up to sixfold. It is useful in

assessing the distribution of radioactivity qualitatively, although it does not

improve resolution. SPECT cameras can be single, dual or triple headed.

SPECT is used in the diagnosis of complex structures such as the spine, pelvis,

hip and temporomandibular joint. One of the most typical applications is the

evaluation of lower back pain or facet joint syndrome. In general, SPECT is not

suitable for the imaging of small, flat or thin bones. Sectional images can be

reconstructed three dimensionally.

(f) Pinhole single photon computed tomography of bone

Pinhole SPECT, a hybrid of pinhole scanning and SPECT, generates

magnified sectional images of a portion of the skeleton. Pinhole SPECT can be

achieved using any single head SPECT gamma camera system provided with a

filtered back-projection algorithm and a Butterworth filter. Pinhole SPECT

simultaneously enhances both the resolution and the contrast by optical magni

fication and tomography, respectively. The value of the limiting spatial

resolution of the planar pinhole scintigraphy is 2 line pair/cm, which is greater

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than the 1 line pair/cm resolution of an ordinary planar scan and similar to

those of CT scans, MRI and ultrasonography.

5.8.1.4. Patient preparation

The rationale for performing the imaging and the details of the procedure

itself should be explained to patients in advance. Unless contraindicated,

patients should be well hydrated by drinking at least two glasses (500 mL) of

water or other beverages between the time of injection and the time of delayed

imaging. Patients should be instructed to urinate immediately prior to delayed

imaging and to drink plenty of fluids for at least 24 hours after radiopharma

ceutical administration.

The following information should be obtained before commencing the

procedure:

—Clinical questions to be resolved by bone scintigraphy;

—History of trauma, infection, oedema, arthritis, neoplasm, metabolic bone

disease or limitation of function;

—Presenting symptoms and signs;

—History of recent scintigraphy, especially with

131

Ga and

111

In;

—Results of prior bone scintigraphy;

—Results of radiography, CT and MRI studies;

—History of therapy that might affect the results of the current study (e.g.

antibiotic, steroid, radiation, diphosphonate or iron therapies, as well as

chemotherapy);

—History of orthopaedic procedures (e.g. nailing repairs and prosthetic

implants) and non-orthopaedic surgery (e.g. ileal conduits), which might

affect the results of bone scintigraphy;

—Breast surgery and implants;

—Relevant laboratory data (e.g. PSA level in patients with prostate cancer);

—History of anatomical–functional renal abnormalities.

5.8.1.5. Clinical contraindications

If possible, elective bone scintigraphy should be deferred in pregnant

women. Similarly, breast feeding should be discontinued for 24 hours after the

injection of the radiopharmaceutical.

5.8.1.6. Observation and interpretation

Attention should be paid to the following points:

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—Observe altered tracer activity in bone, joint, muscle and tendon.

—Note whether increased (or sometimes decreased) activity in the

individual lesion is intense, moderate or mild.

—Identify specifically the bone, joint, muscle and tendon affected.

—Observe if lesions are:

● Single or multiple;

● Focal, diffused or generalized;

● Unilateral, bilateral, axial or appendicular;

● Well or ill defined.

—Describe as accurately as possible the location of the lesion in terms of its

topography (e.g. the epiphysis, metaphysis or diaphysis, cortex, medullary

space, periosteum, joint, muscle or tendon).

—Describe the location in as precise and anatomical terms as possible.

—On follow-up scintigraphy, describe morphologically and semi-quantita-

tively the changes that have occurred since the previous study. The lesions

may be improved, aggravated or unaltered. If any therapy was

performed, evaluate the change in terms of the response. Use caution not

to interpret ‘flare-up’ as aggravation.

—Abnormalities should be interpreted with other available information

including clinical history, physical examination, other imaging studies and

laboratory tests.

—Observe abnormal tracer activity in extramusculoskeletal organs such as

the lungs, liver, spleen, kidneys and bladder.

—Check for artefacts (motion, attenuation objects, urine contamination,

etc.).

5.8.1.7. Reporting

In reporting, be sure to:

(a) Describe the technique used:

— Flow images;

— Blood pool images;

— Delayed images;

— Injection site;

— Magnification or SPECT images (if performed).

(b) Describe abnormal tracer accumulation:

— Increased;

— Decreased;

— Number, site and pattern of abnormal accumulation;

— Bone and joint findings;

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323

— Soft tissue findings.

(d) Compare with previous bone scans.

(e) Draw conclusions:

— Use a narrow differential diagnosis as much as possible.

— Recommend further definitive stud(ies) if the differential diagnosis is

broad.

5.8.1.8. Sources of error

The following sources of error should be noted:

—Injection artefacts;

—Urine contamination or a urinary diversion reservoir;

—Prosthetic implants, radiographic contrast materials or other attenuating

materials that obscure normal structures;

—Surgical deformation;

—Homogeneously increased bone activity (e.g. superscans);

—Motion of patient, table or camera head;

—Greater than necessary collimator-to-patient distance;

—Imaging too soon after injection before radiopharmaceutical has been

optimally cleared from soft tissues;

—Restraint artefacts caused by soft tissue compression;

—Prior administration of a higher energy radionuclide (

131

Ga or

111

In),

or of a

99m

Tc radiopharmaceutical that accumulates in an organ that can

obscure or confound the skeletal activity;

—Radioactivity extraneous to patient;

—Significant findings outside the ROI may be missed if a limited study is

performed;

—Radiopharmaceutical degradation or improper tagging;

—Changing bladder activity during SPECT of pelvic region;

—Lesions without alteration of tracer activity;

—Pubic lesions obscured by underlying bladder activity;

—Renal failure.

5.8.1.9. General methodological considerations

Bone scintigraphy usually starts by imaging the whole skeleton in both

anterior and posterior projections. This is followed by planar spot or pinhole

imaging to highlight the ROI. Standard views may be supplemented by an

oblique or other special view as indicated. Among the special views are the

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Waters’ view of the maxillary bone, the seated view of the sacrum and coccyx,

the ‘butterfly view’ of the sacroiliac joints, the ‘frog-leg view’ of the hip joints,

the ‘sunrise view’ of the patella and the ‘tunnel view’ of the intercondylar notch

of the distal femur. For adequate visualization of the hips, knees and fibulas,

particularly in children, the feet should be turned inwards with the toes close

together (radiographic neutral position or reverse frog-leg view). In general, it

is desirable to take two crossing or orthogonal views whenever one finds

suspicious lesions on one view.

Planar pinhole scintigraphy can be performed using both a single and a

dual head gamma camera system. A pinhole collimator can be aligned to any

desired angle, permitting all-angle imaging, a distinct technical advantage. The

scan time is usually 15–20 min. Aperture sizes of available pinhole collimators

vary from 2 to 6 mm, with 4 mm being the optimal size. A pair of two magnified

images can be obtained by dual head pinhole scintigraphy.

Pinhole SPECT can be achieved by simply substituting a multihole

collimator, used for planar SPECT, by a pinhole collimator. Acquisition, recon

struction and display are the same as in planar SPECT. At present, this

technique is applicable only to the peripheral appendicular bones and joints,

such as those of the ankle and wrist, because of the mechanically limited range

of the detector’s orbit.

Three phase scintigraphy, useful in assessing the vascularity of a bone

lesion, can be interpreted in a semi-quantitative way. It can localize bone

infection and distinguish it from soft tissue lesions. A recommended protocol is

an immediate post-injection angiography (16 consecutive frames of 2–4 s

images), blood pool imaging within 10 min of injection and delayed static bone

imaging after 1.5–4 hours and eventually 24 hours after injection of

99m

Tc-MDP

or -HEDP (the later constitutes a fourth phase).

Indium-111 labelled granulocyte scintigraphy is suitable for the

diagnosis of infective bone diseases. The specificity is about 90%, but

sensitivity is only 50%. This is expensive, and the separation of pure granulo

cytes, which is necessary to increase sensitivity, demands high technical

skills. Formerly,

Ga was used for bone imaging, but nowadays its use is

mostly restricted to osteomyelitis of the spine, where false negative studies

have been reported with

111

In granulocyte scintigraphy. Technetium-99m

labelled anti-granulocyte antibodies,

99m

Tc-HMPAO labelled white blood

cells (WBCs) and

99m

Tc-ciprofloxacin can also be used for diagnosing bone

infections.

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325

5.8.1.10. Interventions

The pelvis can be difficult to evaluate when there is tracer activity in the

bladder. In patients with pelvic symptoms, one or more of the following

additional views are useful:

—A second image taken immediately after voiding.

—An image taken sitting on the detector (oblique or lateral views).

—An image taken after a 24 hour delay.

—A magnified view or SPECT. Single or multiple rapid (acquisition over

5–10 min) SPECT acquisitions are recommended to avoid artefacts

caused by changing activity in the bladder.

—Bladder catheterization should be reserved for those patients who are

unable to void and for whom visualization of the pelvis is essential.

5.8.1.11. Normal and abnormal bone scintigraphy

It is essential to be thoroughly familiar with normal bone findings in order

to accurately recognize pathology. Physiologically, there tends to be a distinct

accumulation of tracer in the cranial vault, facial bones around the nasal cavity,

shoulders, manubriosternal junction, sternoclavicular joints, spine, sacroiliac

joints, pelvis and hips. The larger joints in the extremities may also show

prominent accumulations. It is well known that tracer accumulates intensely in

the physes of growing bones.

Scintigraphic abnormalities of bones and joints are presented as either

increased or decreased uptakes, often described as ‘hot areas’ and ‘cold areas’

respectively. A cold area is also referred to as a photopenic or photon-deficient

area. Increased uptake can be graded as mild, moderate and marked. Among a

range of parameters that may distort scan findings, the tilting of the body to

either side is probably the most critical. Since photon energy diminishes rapidly

according to the inverse distance square law, even a slight difference between

the target–detector distances results in significant image distortion and

asymmetry. Thus, bone structures closest to the detector may appear unusually

hot, leading to an erroneous interpretation.

Bone scintigraphic abnormalities can be recognized in three essential

ways: morphology, tracer uptake pattern and vascularity. Morphological

alterations are expressed in terms of size, shape and position, and radionuclide

uptake pattern and vascularity as increased, unaltered or decreased. Most bone

lesions present as hot rather than cold areas. Lesions that tend to display cold

areas include acute avascular necrosis, lytic metastasis and multiple myeloma.

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5.8.1.12. Clinical applications

Scintigraphy is useful for the following diseases and conditions:

(1) Acute infective diseases of bone;

(2) Tuberculosis of bone;

(3) Non-infective inflammations of bone;

(4) Indium-111 and

99m

Tc labelled leucocytes and

Ga scans in bone

infections;

(5) Transient synovitis of the hip;

(6) Acute pyogenic arthritis;

(7) Osteoarthritis;

(8) Rheumatoid arthritis;

(9) Ankylosing spondylitis;

(10) Reiter’s syndrome;

(11) Reflex sympathetic dystrophy syndrome;

(12) Avascular necrosis of bone;

(13) Osteochondroses;

(14) Traumatic and sports injuries of bone;

(15) Periarticular rheumatism syndromes;

(16) Muscular and musculotendinous rheumatism syndromes;

(17) Metabolic diseases of bone;

(18) Benign and primary malignant bone tumours;

(19) Metastatic bone tumours;

(20) Tumorous conditions of bone.

(1) Acute infective diseases of bone

Acute infective diseases of the bone include osteomyelitis, osteitis,

cortical abscesses and periostitis. Acute osteomyelitis typically involves

metaphysis of the long bones where the end-arteries are distributed,

providing favourable conditions for bacterial embolization. Osteitis, which

commonly occurs in association with osteomyelitis, is the infection of

compact bone. Cortical abscesses are a special form of acute pyogenic

infection in which the infective focus is within the cortex. This occurs either

singly or in conjunction with osteomyelitis. Garre’s sclerosing osteitis is a

variant of chronic osteomyelitis.

Pinhole scintigraphy can distinguish these conditions by specifically

locating the anatomic pathological site and assessing the tracer uptake pattern

of the individual diseases. For example, the metaphyseal bone marrow is

5.8. MUSCULOSKELETAL SYSTEM

327

primarily involved in acute osteomyelitis, the cortical bone in abscesses and the

periosteum in periostitis.

Spondylitis is the acute pyogenic infection of the spine. Infection is either

blood borne or the direct result of a traumatic wound or surgery. Infective

spondylitis, both acute and chronic, produces the characteristic ‘sandwich’ sign

on magnified scintigraphs. This sign consists of intense tracer uptake in two

apposing end-plates with narrowed disc space.

(2) Tuberculosis of bone

Tuberculosis can affect the spine, skull and appendicular bones. Tubercu-

losis is more common in the spine than in other bones. Pathologically, bone

tuberculosis is characterized by destruction with relatively mild reactive bone

formation. With chronicity, it may form cysts accompanied by sclerosis. A

special form of tuberculosis, which involves the finger in infants, is known as

spina ventosa.

Planar bone scan findings are usually not specific, but pinhole scinti-

graphy reveals findings of diagnostic value. The diseased bone shows a

localized area of increased tracer uptake, occasionally with associated

photopenic area(s). The latter finding denotes either necrosis or cystic changes.

In the spine, as in acute infective spondylitis, tuberculosis involves two or more

neighbouring vertebrae and intervertebral discs. Extended tracer uptake can

be seen deep in the vertebral bodies, confirming that the chronic granulo

matous process spreads from the end-plate into the vertebral body.

(3) Non-infective inflammations of bone

Non-infective inflammations of the bone include osteitis condensans ilii,

osteitis pubis, condensing osteitis of the clavicle, sternocostoclavicular hyperos

tosis, infantile cortical hyperostosis and radiation osteitis. Tietze’s disease may

also be included in this category. Each of these diseases manifests characteristic

signs on pinhole images that are comparable to radiographic signs.

(4) Indium-111 and

99m

Tc labelled leucocytes and

Ga scans in bone

infections

White blood cells, either granulocytes or lymphocytes, labelled with

111

99m

Tc and

Ga, are used for the detection of bone infections. Granulocytes

avidly accumulate in acute infective foci while lymphocytes accumulate

primarily in chronic foci. The sensitivity and specificity of

111

In-leucocyte scans

have been variously reported, ranging between 50 and 100%, and 69–100%,

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respectively. Technetium-99m HMPAO labelled leucocytes, anti-granulocyte

monoclonal antibodies and antibiotics labelled with

99m

Tc are used for the same

purpose. The image quality of

99m

Tc-HMPAO leucocyte scans has been

reported to be comparable or superior to that of

111

In-leucocyte scans.

However, there is much normal uptake of

99m

Tc-HMPAO in the axial skeleton,

reducing the diagnostic value. A

99m

Tc-HMPAO leucocyte bone scan is more

suited for the rapid screening of acute infections, whereas

111

In labelled

leucocytes are preferred for chronic cases. Gallium-67 scans are non-specific,

accumulating in both inflammatory and neoplastic lesions.

(5) Transient synovitis of the hip

Transient synovitis, also known as irritable hip syndrome, transient

arthritis or transient coxitis, is a self-limited non-specific inflammatory disease

of the hip in children. Technetium-99m MDP scintigraphy may demonstrate an

ill defined, increased uptake in the hip joint on vascular and static images. In

contrast, pinhole scintigraphy precisely localizes tracer uptake to the synovia,

which cover the femoral head and acetabular fossa. Such uptake is due to an

increase in blood flow through the anastomotic vascular channels in the

inflamed synovium. The tracer uptake may be prominent in the active stage but

rapidly returns to normal with rest and conservative treatment. It is to be noted

that in the early stage with large synovial effusion, tracer uptake may become

reduced due to ischaemia of the femoral head created by capsular distension.

(6) Acute pyogenic arthritis

Like acute osteomyelitis, pyogenic arthritis is difficult to diagnose radio-

graphically in its early stages. However, bone scintigraphy reveals an increased

blood flow and blood pool in septic joints, and intense tracer uptake in the

subchondral bone on static images in the early stages. The ‘wrapped bone’ sign,

which indicates diffuse synovitis, is characteristic. The intensity of subchondral

tracer uptake in acute pyogenic arthritis has been described as roughly paral

lelling the intensity of infection. Dual head pinhole scintigraphy produces a

pair of either the anterior and posterior, or the medial and lateral, images,

permitting a three dimensional analysis of the disease.

(7) Osteoarthritis

Osteoarthritis is the most common disease of the joints. Histologically, it

is characterized by the derangement and eventual destruction of the cartilage

and subchondral bone without obvious inflammation. Synovitis is not a

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constant feature. The involvement is random, pauciarticular and asymmetrical.

The knees, hips and spine are the most common sites. Bone scintigraphs may

show discrete unifocal or multifocal tracer uptake in subchondral bones, and

can be spotty, patchy or segmental in type. When synovitis is present, tracer

uptake becomes diffuse.

(8) Rheumatoid arthritis

Rheumatoid arthritis is characterized by diffuse synovitis, pannus

formation, and cartilagous and bone destruction. Involvement is symmetrical

and polyarticular. Whole body bone scans are the only way to portray

symmetric polyarthritis panoramically; spot views can depict characteristic

changes in both large and small joints in great detail. Pinhole scintigraphy is

useful in delineating many scintigraphic signs of rheumatoid arthritis. Nuclear

angiography provides information on lesional vascularity and on the activity of

the pathological process. In remission, vascularity reverts to normal.

(9) Ankylosing spondylitis

Ankylosing spondylitis and Reiter’s syndrome are the two most common

seronegative spondyloarthropathies (SNSAs). Ankylosing spondylitis is a non-

specific inflammatory disease of the sacroiliac joints and the spine. The disease

primarily involves the synovial components of the sacroiliac joints and the

cartilaginous discovertebral junctions as well as the apophyseal, costovertebral

and neurocentral joints of the vertebrae. In the late stage of the disease, bony

ankylosis of these joints ensues. Planar bone scintigraphy reveals symmetric

intense tracer uptake in the sacroiliac joints and/or spine. Pinhole scintigraphy

can portray the characteristic ribbon-like tracer uptake in the synovial joints of

the spine, producing a ‘bamboo spine’ appearance. In the late stage, tracer

uptake becomes reduced, reflecting a quiescent metabolic state.

(10) Reiter’s syndrome

Reiter’s syndrome is not, as once considered, a rare disease. The

syndrome consists of a triad of urethritis, arthritis and conjunctivitis. The

disease mechanism is still obscure, but an interaction between several different

infective organisms and a specific genetic background is currently being given

serious consideration. Pathologically, the main alterations are present in the

enthesis, which is the site of insertion of a tendon, ligament or articular capsule

into the bone, creating characteristic inflammatory enthesopathy. Typical

clinical manifestations include Achilles tendinitis, calcanean plantar fasciitis