Infection/Inflammation Imaging PDF

# Infection/Inflammation Imaging ## **Tracers** * **Gallium-67 (⁶⁷Ga)-citrate:** recommended for **chronic cases** * **Indium-111 (¹¹¹In) or technetium-99m (^99mTc):** recommended for **acute cases** ## Gallium Imaging * **⁶⁷Ga-citrate:** used to image...

# Infection/Inflammation Imaging ## **Tracers** * **Gallium-67 (⁶⁷Ga)-citrate:** recommended for **chronic cases** * **Indium-111 (¹¹¹In) or technetium-99m (^99mTc):** recommended for **acute cases** ## Gallium Imaging * **⁶⁷Ga-citrate:** used to image both **neoplastic** and **inflammatory diseases**. * **Mechanism by which gallium concentrates in tumor or infection sites:** unknown * **Clinical indications for gallium imaging:** * Localization of sources of **fever of unknown origin.** * Diagnosis of **osteomyelitis.** * Detection of **lung infections in immunocompromised patients.** * Evaluation and monitoring of **inflammatory processes**, such as **sarcoidosis.** ### **Clinical Procedure:** * **Preparation:** No special preparation needed prior to administration of ⁶⁷Ga-citrate. * **Dosage:** 4 to 6 mCi (148-222 MBq) * **Imaging:** Performed 4-72 hr after intravenous injection of the tracer. * **Imaging Techniques:** Planar or tomographic techniques may be performed. ### Image Findings: * **Normal distribution of ⁶⁷Ga-citrate:** * **Nasopharynx, lacrimal glands, salivary glands, bony thorax (ribs, sternum, clavicle, scapulae), external genitalia, liver, kidney (up to 48 hrs after injection), colon contents, pelvis, lumbar spine, sacrum, ileum, ischium**, and in **children** in active epiphyses of **long bones**. * **Liver uptake:** Intense. Liver is the most prominent structure seen in a normal gallium image. * **Kidneys:** Excrete 20-30% of administered dose during the first 24 hours. Renal Activity visualized up to 48 hours after tracer adminstration. * **Persistent renal activity after 48 hours:** Indicates disease. * **Changes in biodistribution:** May result from blood transfusions, chemotherapy, or iron therapy. These changes cause increased gallium concentration throughout the skeleton. * **Recent trauma:** May result in areas of increased uptake. * **Decreased gallium uptake:** May be noted when gadolinium for magnetic resonance imaging has been administered within 24 hours before gallium administration. ### **Technical Considerations:** * **Early Imaging (less than 48 hours):** Patients should be asked to void before pelvis is imaged. * **Delayed Imaging (greater than 48 hours):** Concentration of ⁶⁷Ga within the intestinal contents, particularly within the large bowel, will be visualized. * **Bowel Clearance:** Laxatives or enemas may be prescribed to help decrease activity. * **Bowel Preparations:** Contraindicated in patients who are acutely ill or unable to eat solid food. * **Gastrointestinal Exams:** Radiographic exams of the gastrointestinal tract performed with barium should be scheduled after gallium imaging ## ¹¹¹In-labeled Leukocyte Imaging * **Leukocytes:** White blood cells that accumulate in areas of infection. * **Indium-111 (¹¹¹In):** Radiotracer used to label leukocytes, which permits detection of infection sites using nuclear medicine imaging techniques. * **Common Clinical Indications:** * Detect sources of fever of unknown origin. * Detect sites of inflammatory bowel disease. * Detect osteomyelitis. ### Leukocyte Labeling: * **Procedure:** White cells are isolated from the patient's blood. ¹¹¹In-oxine is added to the leukocytes and binds to components within them. This procedure takes around 2 hours. Strict aseptic technique is crucial. * **Labeling Efficiency:** 70-90% * **Patients Taking Meds:** Steroids, aspirin, or antibiotics will have lower labeling efficiency. It is important to ensure that donor patients receive their own blood back. * **Separation:** White blood cells must be separated from red blood cells and platelets to ensure accurate image results, because platelets concentrate in sites of thrombosis rather than in areas of infection. ### Imaging: * **Adminstration:** Radiolabeled leukocytes are administered within 1-2 hours to ensure viability. * **Imaging Time:** 1-4 or 16-30 hours after the labeled leukocytes are administered. * **Views:** Anterior and posterior views of the head, abdomen, pelvis, and chest, as well as views of the extremities, should be obtained. ### **Technical Considerations:** * **Injection:** Inject labeled leukocytes slowly through a large-gauge needle to avoid damaging the cells. * **Extravasation:** Compromises image quality and may result in a false-negative image if insufficient leukocytes are administered intravenously. ## ^99mTc-labeled Leukocyte Imaging: * **Advantages:** 99mTc is a better tag for gamma cameras. Faster acquisition times, better image quality, and lower absorbed radiation dose. * **Clinical Indications:** Similar to those for ¹¹¹In-labeled leukocytes, but may be more sensitive in the detection of inflammation or ischemia in the small bowel and the detection of acute osteomyelitis. ### **Leukocyte Labeling:** * **Procedure:** Leukocytes are labeled with 99mTc using 99mTc-exametazime (HMPAO). 99mTc-pertechnetate is reconstituted with 99mTc-exametazime and then added to white cells isolated from a sample of the patient's whole blood. Procedure is similar to ¹¹¹In labeling, except that 99mTc-exametazime is added to WBCs suspended in plasma, rather than ¹¹¹In-oxine. ### Imaging: * **Protocol:** Similar to ¹¹¹In-labeled leukocyte imaging. * **Pelvis and Abdomen:** Early imaging of the pelvis and abdomen is critical, because bowel activity appears very early after administration of ^99mTc-labeled leukocytes. * **Collimator:** Low-energy, all-purpose, high-resolution, or parallel-hole collimator with a narrow window centered on 140 keV should be used. * **Single-Photon Emission Computed Tomography (SPECT):** Also possible. ## **Bone Marrow Imaging (Combined White Blood Cell and Sulfur Colloid Imaging):** * **Procedure:** A comparative analysis between normal uptake of ^99mTc sulfur colloid in the bone marrow and ¹¹¹In-labeled white blood cells (WBCs) can be used to determine the origin of infection in either bone marrow or bone itself. ### **^99mTc-sulfur Colloid:** * **Dosage:** 10 mCi (370 MBq) * **Preparation Time:** Freshly prepared technetium 99m (^99mTc) sulfur colloid less than 2 hours old should be used. * **Interval:** At least 30 minutes between injection and imaging should be observed to maximize radiotracer clearance from the circulation. * **Imaging Time:** 10 minutes. ### ¹¹¹In-labeled WBC: * **Procedure:** Labeled and reinjected on the first day. Images are acquired 24 hours later. Marrow imaging can be performed either at the same time as WBC labeling or immediately after completion of WBC labeling. * **Timing:** * If performed before WBC labeling, a low-energy, high-resolution parallel-hole collimator and 15%-20% window centered on 140 keV should be used. * If performed after WBC imaging, a 10% window centered on 140 keV should be used. The rest of the acquisition parameters can remain unchanged. * **Simultaneous Dual Isotope Imaging:** Can be performed with a medium-energy parallel-hole collimator. ## **¹⁸F-FDG Inflammation and Infection Imaging:** * **EANM/SNMMI Guideline:** Available on the SNMMI website and in the reference/suggested reading, below. * **Indications:** Generally, all indications that can be used for WBC imaging for infection and inflammation can be assessed using ¹⁸F-FDG. * **Note:** This technique has limited use clinically, but it should be noted as an alternative to WBC imaging and Gallium-67 citrate imaging.