Lymph glands, lymphatics and tumours

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Chapter 11 Lymph glands, lymphatics and tumours

Positron Emission Tomography Imaging

Positron emission tomography (PET) imaging is a technique used to detect and accurately stage malignant disease, to differentiate benign and malignant tissue, and to assess response to treatment. Until recently, PET imaging availability was restricted due to high capital cost and logistics of radiopharmaceutical supply. It uses short-lived cyclotron-produced radionuclides such as 18Fluorine, 11Carbon, 13Nitrogen and 15Oxygen with half-lives of 110, 20, 10 and 2 min respectively. 18Fluorine is the only one of these that has a half-life long enough to allow it to be produced off-site. This does permit 2-[18F]fluoro-2-deoxy-d-glucose (18F-FDG), the single most important PET radiopharmaceutical, to be used by sites without their own cyclotron.

The widespread acceptance of PET as a major advance is due to two major factors:

1. There is increased recognition in the literature of the role of the main PET tracer 18F-FDG, a glucose analogue that is taken up in tissue in proportion to cellular glucose metabolism. This is particularly useful for tumour imaging, since most tumours have increased glucose metabolism and will concentrate FDG. Malignant cells are characterized by increased glucose transporter molecules at the cell surface. FDG is phosphorylated by the enzyme hexokinase to a polar intermediate which does not cross cell membranes well and is, therefore, trapped in the cell. Hexokinase levels and activity are increased in malignant cells. The reverse reaction (glucose-6-phosphatase) is slow and the enzyme is commonly deficient in cancer cells.
2. Integrated PET CT scanners are now available. These units have separate PET and CT scanners installed in the same gantry. The patient undergoes a conventional CT scan (usually performed with low exposure factors to reduce radiation dose) immediately followed by a PET scan without moving on the same table-top. This allows fusion of the anatomical information from CT with the functional data from the PET scan, and hence accurate anatomical localization of metabolically active disease. The density data from the CT scan is also used to correct the PET data for differential attenuation of the emitted photons within the patient.

Normal physiological uptake is seen in organs that are hypermetabolic and big glucose users especially the brain and the heart, or active or recently active skeletal muscle. Variable uptake is seen in the gut and there is normal excreted urinary activity in the urinary tract. One confounding factor for interpretation may be normal physiological uptake in brown fat – particularly in the neck and paraspinal regions. Differentiation of this normal activity from pathology is greatly aided by the co-registration afforded by combined PET CT scanners.

However, FDG is not specific for cancer cells as any hypermetabolic cell such as those in sites of inflammation or infection will show increased uptake of FDG, so interpretation with reference to full clinical details and other imaging is important to avoid false-positive scans.

As the only PET tracer likely to be widely available in the near future, this section is restricted to FDG imaging. Discussion is also limited to the role of PET in oncological patients.

2-[18F]FLUORO-2-DEOXY-D-GLUCOSE (18F-FDG) PET SCANNING

Indications (oncology)

General

1. Distinguishing benign from malignant disease, e.g. lung nodules, brain lesions, etc.
2. Establishing the grade of malignancy, e.g. brain tumours, soft-tissue masses
3. Establishing the stage of disease, e.g. lung cancer, lymphoma, etc.
4. Establishing whether there is recurrent or residual disease, e.g. lymphoma, teratoma, seminoma, etc.
5. Establishing the site of disease in the face of rising tumour markers, e.g. colorectal, germ cell tumours, etc.
6. Establishing the response to therapy – pre, during and post therapy imaging
7. Identifying occult malignancy, e.g. paraneoplastic syndrome or the unknown primary in the setting of proven metastatic disease.

Specific

The following tumour specific indications are supported by grade A or grade B evidence (A: randomized controlled clinical trials, meta-analyses and systematic reviews; B: robust experimental or observational studies; C: other evidence where the advice relies on expert opinion and has the endorsement of respected authorities):

1. Lung cancer:

a Characterization of solitary pulmonary nodule where biopsy is not possible
b Staging of non-small cell lung cancer prior to surgery or radical radiotherapy.

2. Lymphoma:

a Assessment of residual masses post chemotherapy for disease activity

3. Colorectal cancer:

a Differentiation of local recurrence from post surgical or post radiotherapy fibrosis
b Exclusion of distant metastases prior to resection

4. Oesophageal cancer:

a Primary staging

5. Melanoma:

a Detection of distant metastases (sentinel node mapping preferred for regional nodal disease)

6. Thyroid cancer:

a Raised thyroglobulin; negative I-131 scan

7. Seminoma/teratoma:

a Assessing recurrent disease from seminoma or teratoma
b Residual masses post treatment

8. Soft-tissue sarcoma:

a Staging and grading

9. Other indications; there are other scenarios where PET may well be useful, but either the numbers are smaller or the evidence is more limited or less robust.

Contraindications

1. Recent chemotherapy – minimum interval of 2–3 weeks recommended
2. Recent radiotherapy – minimum interval of 8–12 weeks recommended
3. Poorly controlled diabetes, i.e. serum glucose >8.5 mmol l−1 at time of scanning.

Patient preparation

1. Fasting for 4–6 h, with plenty of non-sugary fluids
2. Monitor blood glucose before injection to ensure it is not elevated. Elevated blood glucose levels result in diversion of glucose to muscle. Consider rescheduling patient if blood glucose elevated. Administration of insulin is counter-productive as this diverts glucose uptake to muscle
3. A mild sedative such as diazepam may be given to reduce physiological muscle and brown fat uptake
4. Oral contrast may be administered to aid interpretation of the CT. Attenuation correction artifact on the PET images secondary to the high-density contrast has been shown not to be clinically significant.

Technique

1. Up to the UK limit of 400 MBq 18FDG intravenously (i.v.) (10 mSv effective dose (ED)) is administered.
2. To reduce muscle uptake of FDG, patients should remain in a relaxed environment such as lying in a darkened room (without talking if head and neck area are being imaged) between injection and scan.
3. Image at 1 h post injection. Later imaging has been reported to enhance tumour conspicuity due to a higher tumour to background ratio.
4. Imaging is preferred with the arms above the head to reduce beam hardening artifact on the CT.
5. CT:

a Low dose
b No i.v. contrast medium
c Positive or negative oral contrast agents according to local protocol are increasingly being used.

6. PET:

a From the base of skull to upper thighs (occasionally extended if melanoma or limb or head and neck tumours)
b 3–4 min for each of 5–6 bed positions for the PET

7. In some instances a diagnostic standard dose CT with i.v. contrast may be acquired as well, but in routine practice a diagnostic scan will usually be already available.

Other applications

Coronary artery disease (Chapter 8)

Assessment of myocardial viability.

Neurology (Chapter 13)

1. Location of epileptic foci
2. Assessment of dementia.

Further reading

British Nuclear Medicine Society Web Site guidelines –. www.bnms.org.uk, 2008.

.

Cook G.J., Wegner E.A., Fogelman I. Pitfalls and artifacts in 18FDG PET and PET/CT oncologic imaging. Semin. Nucl. Med.. 2004;34(2):122-133.

Kapoor V., McCook B.M., Torok F.S. An introduction to PET CT imaging. RadioGraphics. 2004;24(2):523-543.

Rohren E.M., Turkington T.G., Coleman R.E. Clinical applications of PET in oncology. Radiology. 2004;231(2):305-332.

von Schulthess G.K., Steinert H.C., Hany T.F. Integrated PET/CT: current applications and future directions. Radiology. 2006;238(2):405-422.

Gallium Radionuclide Tumour Imaging

This is rarely used, having almost entirely been superseded by cross-sectional techniques and PET scanning.1 The main disadvantages are the high radiation dose, the extended nature of the investigation, its non-specific nature, and difficulties in interpretation in the abdomen due to normal bowel activity.

Indications

1. Hodgkin’s and non-Hodgkin’s lymphoma: assessment of residual masses after therapy and early diagnosis of recurrence1
2. Gallium imaging has been used with variable success in a variety of other tumours, e.g. hepatoma, bronchial carcinoma, multiple myeloma and sarcoma
3. It has also been used in benign conditions such as sarcoidosis and for localization of infection or in suspected orthopaedic infection

Contraindications

None.

Radiopharmaceutical

67Ga-Gallium citrate, 150 MBq maximum (17 mSv ED).

Normal accumulation is seen in the liver, bone marrow and nasal sinuses, and variably in the spleen, salivary and lacrimal glands. There is significant excretion via the gut and some via the kidneys. 67Ga has a half-life of 78 h and principal γ-emissions at 93, 185 and 300 keV, so image quality is fairly poor.

Equipment

1. Gamma camera, preferably with whole-body and single-photon emission computed tomography (SPECT) facilities
2. Medium- or high-energy collimator.

Patient preparation

If the abdomen is being investigated, laxatives may be given (if not contraindicated) for 2 days after injection of 67Ga-citrate to clear bowel activity. Additionally, an enema or suppository may be given on the day of imaging.

Technique

1. 67Ga-citrate is administered i.v.
2. Delayed images are acquired as below with energy windows about the lower two or all three of the main photopeaks.

Images

1. 48 and 72 h. Whole-body, spot views and SPECT as appropriate. SPECT can increase the sensitivity and specificity of the investigation
2. Non-specific bowel activity can be discriminated by imaging on two separate occasions. Activity in bowel contents should move between scans and abnormal areas of accumulation will be stationary. If there is still any doubt at 72 h, later images at up to 7 days may prove helpful.

Additional techniques

1. A radionuclide bone scan may be performed prior to gallium imaging.
2. A radiocolloid scan may help to discriminate between lesions in the region of the liver or spleen and normal uptake in these organs. Image subtraction techniques may be used.

Aftercare

Normal radiation safety precautions.

Complications

None.

Reference

1 Seam P., Juweid M.E., Cheson B.D. The role of FDG-PET scans in patients with lymphoma. Blood. 2007;110(10):3507-3516.

Further reading

Bombardieri E., Aktolun C., Baum R.P., et al. 67Ga scintigraphy: procedure guidelines for tumour imaging. Eur. J. Nucl. Med. Mol. Imaging.. 2003;30(12):BP125-131.

.

Front D., Bar-Shalom R., Israel O. The continuing clinical role of gallium 67 scintigraphy in the age of receptor imaging. Semin. Nucl. Med.. 1997;27(1):68-74.

Radioiodine Metaiodobenzylguanidine Scan

Metaiodobenzylguanidine (MIBG) is a noradrenaline (norepinephrine) analogue. It is taken up actively across cell membranes of sympathetic and adrenal medullary tissue into intracellular storage vesicles. There is no further metabolism, and it remains sequestered and localized in the storage vesicles of catecholamine-secreting tumours and tumours of neuroendocrine origin.1

Indications

Localization and staging of the following tumours of neuroendocrine origin:

1. Neuroblastoma
2. Phaeochromocytoma
3. Carcinoid tumours
4. Medullary thyroid carcinoma
5. Other neuroendocrine tumours.

Contraindications

None.

Radiopharmaceuticals

1. 123Iodine(I)-metaiodobenzylguanidine (MIBG), 250 MBq typical, 400 MBq max (6 mSv ED with thyroid blockade). The 13-h half-life of 123I allows imaging up to 48 h
2. 131I-labelled MIBG is also available, and is still in common use outside Europe where 123I-MIBG is not made commercially. However, the higher photon energy of the emitted gamma rays renders it an inferior imaging agent and results in a higher radiation dose to the patient. It should only be considered where 123I-MIBG cannot be obtained.

Equipment

1. Gamma-camera, preferably with whole-body imaging and SPECT capabilities
2. Low-energy general purpose collimator for 123I.

Patient preparation

1. Where possible, stop medications that interfere with MIBG uptake.2 These include tricyclic antidepressants, antihypertensives, cocaine, sympathomimetics, decongestants containing pseudoephedrine, phenylpropanolamine and phenylephrine (many available over the counter) and others.
2. Thyroid blockade, to reduce radiation dose to the thyroid continuing for 24 h after 123I-MIBG injection:

a Adults – either oral potassium perchlorate (400 mg, 1 h before MIBG injection, then 200 mg every 6 h) or oral potassium iodate (85 mg twice daily starting 24 h before MIBG injection)
b Children – Lugol’s iodine 0.1–0.2 ml diluted with water or milk three times a day starting 48 h before MIBG injection. Potassium iodate is more palatable – the tablets need splitting for paediatric dosage.

Technique

1. MIBG is administered slowly i.v. over 1–2 min (a fast injection may cause adrenergic side-effects).
2. Imaging at 24 h (sometimes additionally at 4 or 48 h), emptying bladder before pelvic views.

Images

1. Anterior and posterior abdomen, 10–20 min per view
2. Whole-body imaging for comprehensive search for metastases
3. SPECT may help to localize lesions, particularly in thorax and abdomen. Hybrid CT-SPECT scanners will help anatomical localization.

Additional techniques

1. If therapy with 131I-MIBG is being considered, quantitative assessment can be performed using geometric mean and attenuation correction to calculate percentage of administered dose residing in tumour at 24 h.
2. 111In-octreotide, which binds to somatostatin receptors frequently expressed in neuroendocrine and other tumours, is an alternative imaging agent to MIBG. It appears to be more sensitive for carcinoids, and may be useful in cases where the MIBG scan is negative. It also has therapeutic analogues under development.

Aftercare

Normal radiation safety precautions (see Chapter 1).

Complications

None.

References

1 Ilias I., Pacak K. Current approaches and recommended algorithm for the diagnostic localization of pheochromocytoma. J. Clin. Endocrinol. Metab.. 2004;89(2):479-491.

2 Solanki K.K., Bomanji J., Moyes J., et al. A pharmacological guide to medicines which interfere with the biodistribution of radiolabelled meta-iodobenzylguanidine (MIBG). Nucl. Med. Commun.. 1992;13(7):513-521.

Somatostatin Receptor Imaging

Somatostatin is a physiological neuropeptide which has biological effects including inhibition of growth hormone release, and suppression of insulin and glucagon excretion. Octreotide (a long-acting analogue of the human hormone, somatostatin) can be used therapeutically to inhibit hormone production by carcinoids, gastrinomas and insulinoma, etc. A number of tumours, particularly those of neuroendocrine origin, express neuroendocrine receptors. Imaging after the administration of radionuclide-labelled somatostatin analogues such as octreotide, therefore, allows their localization.1

Indications

Localization and staging of the following tumours of neuroendocrine origin:

1. Carcinoid
2. Gastrinoma
3. Phaeochromocytoma
4. Medullary cell Ca thyroid
5. Small cell lung cancer
6. Pituitary.

Although sometimes used for the assessment of insulinomas, these latter tumours are more variably visible with octreotide (approx. 50%) than carcinoids, gastrinomas and phaeochromocytomas, which are seen in 80–100% of cases.

Contraindications

None.

Radiopharmaceuticals

111Indium (In) pentetreotide (a DTPA conjugate of octreotide) 220 MBq i.v. (ED 17 mSv).

Equipment

1. Gamma-camera, preferably with whole-body imaging and SPECT capabilities
2. Medium energy for 111In.

Patient preparation

1. Some centres use bowel preparation
2. Oral hydration to help with renal clearance. There is usually high renal uptake
3. In patients with possible insulinoma i.v. glucose should be available because of a small risk of inducing hypoglycaemia
4. Discontinue oral somatostatin to avoid competitive inhibition.

Technique

Image at 24 h and 48 h if necessary:

1. Anterior and posterior abdomen, 10–20 min per view
2. Whole-body imaging for comprehensive search for metastases
3. SPECT may help to localize lesions, particularly in thorax and abdomen. Hybrid CT-SPECT scanners will help anatomical localization.

Additional techniques

MIBG may be positive in octreotide negative tumours and vice versa.

Aftercare

Normal radiation safety precautions (see Chapter 1).

Complications

None.

Reference

1 Krenning E.P., Kwekkeboom D.J., Bakker W.H., et al. Somatostatin receptor scintigraphy with [111In-DTPA-D-Phe1] and [123I-Tyr3]-octreotide: the Rotterdam experience with more than 1000 patients. Eur. J. Nucl. Med.. 1993;20(8):716-731.

Lymph Node Imaging

RADIOGRAPHY

On plain films lymph nodes may show:

1. Directly:

a as a soft tissue mass, e.g. hilar lymph glands on a chest X-ray
b calcified nodes, e.g. following tuberculosis or treatment of malignancy

2. Indirect evidence from displacement of normal structures, e.g. displacement of ureters seen during excretion urography.

ULTRASOUND

Advantages:

1. Non-invasive and without risk to the patient
2. Helpful in the neck and axilla in particular, especially with Doppler analysis and US-guided fine-needle aspiration or core biopsy

Disadvantages:

1. Highly operator-dependent
2. Intestinal gas is a major factor in poor visualization. Unsuitable for the mediastinum.

COMPUTED TOMOGRAPHY

Technique is dealt with in other chapters.

Advantages:

1. Can image all nodes
2. Technically easy to perform.

Disadvantages:

1. Internal structure is not seen
2. Gives no indication of nature, apart from on the basis of size, and possibly on basis of enhancement characteristics.

MAGNETIC RESONANCE IMAGING

Technique is dealt with in other chapters.

Advantages:

1. Can image all nodes
2. Technically easy to perform.

Disadvantages:

1. Internal structure is not seen
2. Gives no indication of nature, apart from on the basis of size.

MAGNETIC RESONANCE LYMPHANGIOGRAPHY

Currently under assessment is MR lymphangiography. High-resolution T2*-weighted MR scans are obtained prior to and post the injection of lymphotropic superparamagnetic nanoparticles. Normal nodes are high signal on the pre-contrast scan, but lose signal on the post contrast signal due the T2* effect from the iron content in the particles taken up by normal reticuloendothelial cells. Nodes containing malignant tissue retain their high signal intensity on the post contrast scans and small tumour deposits can be detected in even normal-sized nodes.1

RADIOGRAPHIC LYMPHANGIOGRAPHY

This is a technically difficult and invasive examination requiring limited operative exposure of lymphatic vessels for cannulation, usually in the feet. Lipiodol, the usual contrast material, is no longer available and operator expertise is also largely no longer available. It has been superseded by cross-sectional imaging techniques such as US, CT and MRI, and functional assessment with FDG PET and some other radionuclide imaging procedures.

RADIONUCLIDE LYMPHOSCINTIGRAPHY

Lymphoscintigraphy provides a less invasive alternative to conventional lymphography. High-resolution anatomical detail is not possible.

Indications

1. Localization of the ‘sentinel’ node in breast carcinoma2 and malignant melanoma using a hand-held probe. In recent years, this has become the major indication for lymphoscintigraphy. The technique in itself does not diagnose nodes affected by malignancy; rather it identifies the node most likely to be involved and, therefore, to allow histological sampling. Although still awaiting completion of long-term clinical trials, the early indications are that if the first or ‘sentinel’ node in the lymphatic drainage chain from the primary site is shown to have negative histology (approx. 60% of cases in breast cancer), then more extensive nodal clearance and associated morbidity can be avoided
2. Differentiation of lymphoedema from venous oedema
3. Assessment of lymphatic flow in lymphoedema.3

Contraindications

Hypersensitivity to human albumin products.

Radiopharmaceuticals

1. 99mTechnetium (Tc)-nanocolloidal albumin (particle size <80 nm), 40 MBq maximum (0.4 mSv ED) total for all injections. The colloid is injected intradermally and cleared from the interstitial space by lymphatic drainage.
2. A number of other colloids are used around the world for sentinel node imaging, and other radiopharmaceuticals have been used for lymphoscintigraphy.

Equipment

1. Gamma-camera
2. High-resolution general purpose collimator.

Patient preparation

Clean injection sites.

Technique

1. Sentinel node imaging:

Example protocols are:

a breast carcinoma: inject 99mTc-colloid in approximately 5 ml volume intradermally for palpable lesions and around the tumour under US guidance for non-palpable lesions
b melanoma: inject 99mTc-colloid intradermally in a ring of locations around the melanoma site, with a volume of about 0.1 ml for each injection.

Static images are taken at intervals until the first node is seen. For breast cancer, take anterior and left or right lateral images with the arm raised as for surgery. Mark the skin over the node in both axes to guide surgical incision and intraoperative location with a gamma-detecting probe.
With effectively no background activity in the body, anatomical localization on the images is needed. A 57Cobalt flood source (usually available for routine camera quality assurance) can be placed for a short period under the imaging couch to produce a body outline on the image.

2. Other anatomical sites of investigation or for investigation of lymphatic drainage/lymphoedema:

a 99mTc-colloid in 0.1–0.3 ml volume is injected intradermally at sites depending upon the area to be studied, e.g. for nodes below diaphragm and lower limb drainage – injections in each foot in the first and second web spaces for drainage or over the lateral dorsum of the foot for lymphatics or for axillary nodes and upper limb drainage injections in each hand in the second and third web spaces.
b Static images are taken of the injection site(s) immediately, followed by injection site, drainage route and liver images at intervals, e.g. 15, 30, 60 and 180 min, continuing up to 24 h or until the liver is seen. Visualization of the liver indicates patency of at least one lymphatic channel (except early liver activity within 15 min, which implies some colloid entry into blood vessels).

Analysis

If more frequent imaging or a long dynamic study is performed, time-activity curves for regions along the drainage route can be plotted and used to quantify flow impairment.

Aftercare

Normal radiation safety precautions.

Complications

Anaphylactic reaction – rare.

References

1 Harisinghani M.G., Barentsz J., Hahn P.F., et al. Noninvasive detection of clinically occult lymph-node metastases in prostate cancer. New Engl. J. Med.. 2003;348(25):2491-2499.

2 Krynyckyi B.R., Kim C.K., Goyenechea M.R., et al. Clinical breast lymphoscintigraphy: optimal techniques for performing studies, image atlas, and analysis of images. RadioGraphics. 2004;24(1):121-145.

3 Witte C.L., Witte M.H., Unger E.C., et al. Advances in imaging of lymph flow disorders. RadioGraphics. 2000;20(6):1697-1719.

Radionuclide Imaging of Infection and Inflammation

A number of radionuclide techniques exist for this, the most commonly used of which is radionuclide-labelled leucocyte imaging.1,2 The ready availability and sensitivity for collections and inflammation of anatomical imaging techniques such as US and CT has, however, reduced the demand for radionuclide procedures.

Indications

1. Diagnosis and localization of obscure infection and inflammation in soft tissue and bone
2. Assessment of inflammatory activity in disorders such as inflammatory bowel disease, e.g. Crohn’s.

Contraindications

None.

Radiopharmaceuticals

1. 111In-labelled leucocytes, 20 MBq maximum (9 mSv ED). 111In-oxine, tropolonate and acetylacetonate are highly lipophilic complexes that will label leucocytes, erythrocytes and platelets. The leucocytes have to be labelled in vitro and the labelled cell suspension reinjected. ABO/Rh-matched donor leucocytes can be used with neutropenic patients or to reduce infection hazard in HIV-positive patients.111In has a half-life of 67 h and principal gamma emissions at 171 and 245 keV. There is no confounding uptake in bowel and this technique may be more suitable for chronic or more low-grade infections because of the longer imaging window (4–48 h).
2. 99mTc-hexamethylpropyleneamineoxime (HMPAO)-labelled leucocytes, 200 MBq max (3 mSv ED). HMPAO is also a highly lipophilic complex which preferentially labels granulocytes. The cell-labelling technique is similar to that for 111In, but HMPAO has the advantage that kits can be stocked and used at short notice. There is more bowel uptake as a result of biliary excretion than with 111In-labelled leucocytes, so images must be taken earlier than 4 h post injection for diagnosis of abdominal infection. The 99mTc label delivers a lower radiation dose than 111In-labelled leucocytes and has better imaging resolution, which can, for example, help to identify inflammation in small bowel.
3. 67Ga-gallium citrate, 150 MBq max (17 mSv ED). This localizes in inflammatory sites. Formerly the most commonly used agent, it has now largely been replaced by labelled leucocyte imaging. There is significant bowel activity up to 72 h, so delayed imaging may be necessary for suspected abdominal infection, and accuracy in the abdomen is less than elsewhere. 67Ga, with a T1/2 of 78 h and principal γ-emissions at 93, 185 and 300 keV, delivers a significantly higher radiation dose than 99mTc-HMPAO- and 111In-labelled leucocytes, but it has the advantage of requiring no special preparation.
4. 99mTc- or 111In-human immunoglobulin (HIG). This is a newer agent for which a commercial kit is available for 99mTc labelling. It has the advantage of not requiring a complex preparation procedure, but its place relative to labelled leucocytes is still a matter of debate.
5. 99mTc-sulesomab (Leukoscan). This is another more recent commercial agent comprising a labelled antigranulocyte monoclonal antibody fragment. It also has a simple preparation procedure, and is finding a role in the diagnosis of orthopaedic infections.
6. 18F-FDG PET has been used to evaluate obscure infection or suspected infection of orthopaedic hardware.

Equipment

1. Gamma camera, preferably with whole body imaging facility
2. Low-energy high-resolution collimator for 99mTc, medium-energy for 111In, medium- or high-energy for 67Ga.

Patient preparation

None.

Technique

1. The radiopharmaceutical is administered intravenously
2. Image timing depends upon the radiopharmaceutical used and the suspected source of infection. Whole-body imaging may be employed for all of the radiopharmaceuticals:

a 111In-labelled white cells. Static images are acquired at 3 and 24 h post injection. Further imaging at 48 h may prove helpful.
b 99mTc-HMPAO-labelled white cells. For suspected abdominal infections, image at 0.5 and 2 h, i.e. before significant normal bowel activity is seen. For other sites, image at 1, 2 and 4 h. Additional 24-h images may be useful.
c 67Ga-citrate. Images are acquired at 48 and 72 h for regions where normal bowel, urinary and blood pool activity may obscure abnormal collection sites. Later images may prove helpful in non-urgent cases. Extremities and urgent cases may be imaged from as early as 6 h. If not contraindicated, laxatives given for 48 h post injection will help to clear bowel activity.

Additional techniques

1. The diagnosis of bone infection may be improved by combination with three-phase radioisotope bone scanning or bone marrow imaging.
2. Comparison with a radiocolloid scan may help to discriminate between infection in the region of the liver or spleen and normal uptake in these organs.

Aftercare

Normal radiation safety precautions (see Chapter 1).

Complications

None.

References

1 Peters A.M., Lavender J.P. Editorial. Imaging inflammation with radiolabelled white cells; 99mTc-HMPAO or 111In? Nucl. Med. Commun.. 1991;12:923-925.

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2 Love C., Palestro C.J. Radionuclide imaging of infection. J. Nucl. Med. Technol.. 2004;32(2):47-57.

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