Chapter 20: Diagnostic investigations
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Source: Adapted from Henkin ([64]), Peter and Gambhir ([121]), Ziessman et al. ([179]).
Diagnostic radioisotope procedures (nuclear medicine)
Definition
Nuclear medicine involves the administration of radioactive material in the form of a radiopharmaceutical to patients for diagnosis or therapy (DH [36], HPA [62]). In both cases, the radioactive material is attached to a pharmaceutical chosen according to the organ or system to be investigated or treated. For example, radioactively labelled phosphates will be concentrated in the bone and are therefore used for bone scans, whereas radioactive iodine (given in the form of sodium iodide) concentrates in the thyroid and is used for both imaging and treating various thyroid conditions, forming a radiopharmaceutical (DH [36], HPA [62]).
A radionuclide investigation involves administration of the appropriate radiopharmaceutical and using dynamic imaging or waiting a predetermined time to allow the radiopharmaceutical to be taken up in the organ to be investigated (Table 20.4). The patient is then positioned on the camera table, usually lying flat, and is required to keep still during the scan. Movement causes artefacts which reduce diagnostic accuracy. The scan may last 15–60 minutes (DH [36]).
Table 20.4 Radionuclide investigations
| Investigation/target organ | Radiopharmaceutical | Procedures and clinical interventions |
|---|---|---|
| Imaging studies | ||
| Bone scan | ||
| Used to assess bone function in which malignancy, fractures and diseases such as osteomalacia and Paget's disease can be diagnosed | Technetium (99mTc) phosphate and phosphonate compounds, including methylene diphosphonate (MDP) and hydroxymethylene diphosphonate (HDP) | Patient to drink 5–6 cups of fluid and to empty bladder regularly while waiting for scan. This is to enhance soft tissue clearance and minimize absorbed radiation dose to the bladder |
| Renogram (dynamic renal study) | ||
| Used to assess renal function by monitoring clearance of radiopharmaceutical via kidneys | 99mTc MAG3 Benzoylmercaptoacetyltriglycine 99mTc DTPA (diethylenetriamine penta‐acetic acid) | Patients to drink approximately 600 mL of fluid and to empty bladder prior to scan, which takes approximately 1 hour
Intravenous diuretic is to be administered to patient during the scan to diagnose obstructive uropathy (Russell [142]) |
| Static renal study | ||
| Used to assess size, shape, position and function of kidneys. Used to diagnose renal scarring in children | 99mTc DMSA (dimercaptosuccinic acid) | No preparation |
| Perfusion lung scan | ||
Used to assess blood supply to alveolar tree. Provides complementary information to a ventilation lung scan
Used to diagnose pulmonary embolism | 99mTc MAA (macroaggregated albumin) | Radiopharmaceutical is administered as a slow bolus intravenous injection. Patient to lie supine and breathe deeply while injection is being given. This is to enhance even distribution of MAA through the lung capillary bed. If the patient is pregnant, administered activity or dose needs to be reduced |
| Ventilation lung scan | ||
| Provides complementary information to a perfusion lung scan in diagnosis of pulmonary embolism. Used to assess patency of airways | 99mTc Technegas, 99mTc aerosol, 81mKr gas, 133Xe gas | A chest X‐ray performed within the preceding 24 hours is required prior to scan, to assist with interpretation of lung scan. Patient breathes the radiopharmaceutical through a special mouthpiece while scan is being performed |
| Cardiac studies: perfusion imaging | ||
| Used to assess areas of viable perfused myocardium. This is a two‐part test with myocardial perfusion monitored under stress and subsequently at rest. Stress may be exercise or pharmacologically induced. Often performed on patients with suspected coronary artery disease, recent myocardial infarction or those who have undergone coronary artery bypass surgery | 99mTc MIBI (methoxyisobutyl isonitrile), 99mTc tetrafosmin, 201Tl thallous chloride | Patient vital signs need to be closely monitored during post‐exercise period because there is the potential risk of triggering a myocardial infarction after stress
This test is usually performed within a cardiology unit with appropriately trained personnel and equipment. Patient is usually kept in the department until they have been assessed by a clinician |
| Cardiac studies: left ventricular ejection fraction/multiple gated acquisition scan | ||
| Used to evaluate cardiac function in patients prior to and during courses of chemotherapy containing cardiotoxic agents such as epirubicin | 99mTc‐labelled red blood cells | Current weight of patient is required for calculation of dose of a red blood cell labelling agent, which ensures red blood cells are labelled with required radioactivity. The volume calculated is then administered intravenously 20–30 minutes prior to scan. Patient lies supine for 30–40 minutes |
| Thyroid scan | ||
| May be used to confirm presence of one or more nodules within the thyroid, or to identify functional characteristics of nodule(s) | 99mTc pertechnetate, 123I/124I/131I sodium iodide | Patient to avoid foods containing iodine (including sea salt, seafood, cod liver oil, mineral tablets and kelp) for 3 days prior to test. These foods decrease uptake of radiopharmaceutical within thyroid bed. Patient to discontinue thyroid medication for between 3 days and 3 weeks prior to test, depending on specific instructions given by clinician |
| Parathyroid scan | ||
| Used to diagnose parathyroid adenomas in patients with primary hyperparathyroidism | 99mTc pertechnetate, 201Tl thallous chloride | This is a two‐part test, comprising a thyroid scan which is completed prior to the parathyroid scan. Patient should follow instructions for thyroid test |
| Tumour imaging | ||
| Used to differentiate between metabolically active tumours and space‐occupying lesions, or for the diagnosis of unknown primary tumours | 18F 2‐fluorodeoxyglucose (FDG) | Patient to fast for up to 6 hours prior to injection, with only water to be taken. Patients may experience a metallic taste in the mouth immediately after administration. Waiting interval between injection and scan is 30 minutes, scan being performed with a positron emission tomography (PET) camera |
| Used to diagnose infection and diagnose and stage cancers such as lung, Hodgkin disease lymphomas and neuroendocrine tumours | 67Ga gallium citrate | Due to excretion of gallium citrate via the gastrointestinal tract, patients should be given laxatives or encouraged to increase fibre and fluid intake to avoid constipation |
| Used to diagnose and assess patients with neuroectodermal tumours including phaeochromocytomas, neuroblastomas, carcinoid, medullary thyroid cancers and paragangliomas | 123I mIBG (meta‐iodobenzylguanidine) | Patient must take Lugol's iodine or potassium iodide for 2 days prior to and 3 days after day of administration. mIBG may cause hypertension and is administered slowly over a 10‐minute period. On occasions, patients may experience some discomfort at the injection site. This may be relieved by applying heat to the area of discomfort and reducing rate of infusion. For paediatric patients, it is preferable to administer mIBG via a central venous catheter. Some drugs that act on the adrenergic system may interfere with uptake of mIBG |
| Often used in conjunction with mIBG scans to assist with localization of the primary tumour and sites of metastatic spread in the aforementioned diseases, e.g. neuroendocrine tumours | 111In octreotide
DTPA‐d‐Phe‐1‐octreotide | Patients with insulinoma should have their blood sugar levels monitored before and after injection. An intravenous solution containing glucose should be available in case of hypoglycaemia. Patients should be encouraged to increase fluid and fibre intake to avoid constipation |
| Sites of infection | ||
| To identify areas of lymphocyte localization in patients with either acute or chronic inflammatory infections | Labelled white blood cells | 50 mL of blood is taken from patient using a 19 G needle. Labelled blood is reinjected after approximately 2 hours, following which patient is scanned later the same day and/or the following day |
| Gastrointestinal tract | ||
| To determine cause of gastrointestinal bleeding, including Meckel's diverticulum | 99mTc pertechnetate | Patients (usually children) need to fast for 4–6 hours before scan; adults to fast from midnight |
| Non‐imaging studies | ||
| Kidney function | ||
| Measurement of glomerular filtration rate (GFR) provides an assessment of renal function. Often used in renal transplant patients, in compromised renal function due to long‐term use of certain drugs (e.g. ciclosporin) or in patients with systemic lupus erythematosus. Oncology patients often have renal function assessed prior to chemotherapy, particularly if regimen includes platinum‐based cytotoxic agents | 51Cr EDTA (ethylenediamine tetra‐acetic acid) | Renal clearance of administered radiopharmaceutical is assessed from residual radioactivity in blood samples taken from patient at either 3 hours, or at 2, 3 and 4 hours post injection. Patient's height and weight are required to enable GFR to be calculated accurately. It is important that no hydration or blood products are commenced during the test as this may alter results of test |
| Red cell mass/plasma volume | ||
| Often used to diagnose polycythaemia vera in patients with cardiovascular disease | 125I human serum albumin, 51Cr or 99mTc‐labelled red blood cells | 10 mL of blood is taken from patient using a 19 G needle. Labelled blood is re‐injected after approximately 1.5 hours, following which patient's blood is taken at 10‐minute intervals for 40 minutes. Patient's height and weight are recorded |
| Sentinel node localization. Sentinel lymph nodes receive drainage from the breasts (Luini et al. [95]). By undertaking biopsies of these nodes, the surgeon can predict the cancer status of all nodes in the axillary region. This procedure allows for accurate diagnosis of the patient's cancer status, avoiding unnecessary axillary dissection (Schrenk et al. [144]) | 99mTc colloid | 0.1–0.2 mL is injected intradermally into the designated area on the breast for location of main sentinel node. Minimum of 1 hour (up to 24 hours) prior to surgical procedure
During the procedure all staff must wear their film badges and those handling the specimen must wear finger dosimeters. The theatre door should be labelled with a warning controlled area sign and disposable drapes and gowns should be used. The specimen should be placed in a screw‐top container, which is labelled with the radioactive symbol and the details recorded in the log book. The specimen is then stored for 48 hours in a temperature monitored fridge, after which time it is sent to histopathology in the normal way. The radioactive label is removed in histology after 1 week when the specimen is then considered non‐radioactive |
| On completion of the procedure, the used drapes, gown and gloves should be placed in a hospital approved clinical waste bag and the environment and waste monitored to ensure no contamination is present. Any contaminated items should be marked radioactive and stored in a secure store until sufficient radioactive decay has occurred. Only then should the warning symbols be removed by the physics department and the waste disposed of as clinical waste | ||
