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Endocrine System

Endocrine System. In-vivo imaging and non-imaging applications in NM has a significant role in understanding the function and disorders of the endocrine systemThyroid, parathyroid, and adrenal glands most common.No other imaging or non-imaging procedures exists for other glands . Adrenal Gland Im

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Endocrine System

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    1. Endocrine System Small group of organs with a principal function of secreting hormones Hormones have regulatory effects on metabolic and biochemical processes throughout the body Endocrine glands consists of: >pituitary gland (anterior/posterior) >thyroid gland >parathyroid gland >islet cells of the pancreas >adrenal glands (cortex/medulla) >gonads (ovaries/testes)

    2. Endocrine System In-vivo imaging and non-imaging applications in NM has a significant role in understanding the function and disorders of the endocrine system Thyroid, parathyroid, and adrenal glands most common. No other imaging or non-imaging procedures exists for other glands

    3. Adrenal Gland Imaging Located at superior poles of the kidneys. Consist of outer cortex and inner medulla Cortex produces steroid hormones (aldosterone,cortisol) Medulla manufactures catecholamines (epinephrine/norepinephrine) hormones that control bodies response to stress

    4. Adrenal Gland Imaging Tumors of the adrenal medulla sre called Pheochromocytomas Symptoms include increased levels of epinephrine/non-epinephrine in blood and urine. NM used to identify sites of increased epinephrine/norepinephrine within adrenal bed and outside metastatic sites.

    5. Adrenal Gland Imaging Radiopharmaceutical used to image the adrenal medulla is I-131 methyliodobenzylguanidine (MIBG) Compound is structurally the same as norepinephrine, does not exert same effect.

    6. Adrenal Gland Imaging 1 day prior to injection, patient prep receives Lugols solution (potassium iodide) Solution saturates the thyroid gland preventing uptake of I-131 (minimize unnecessary exposure to thyroid) 0.5mCi I-131 administered IV.

    7. Adrenal Gland Imaging Anterior and Posterior images acquired at 1,3, and 7 days PI. (skull to pelvis) Patient is asked to void prior to study. Uptake normally in liver, spleen, and heart. Salivary glands and bladder may also be visualized.

    8. Adrenal Gland Imaging Metastases from Pheochromocytomas may be visualized in liver, bone, lymph nodes, heart, and lungs.

    9. Thyroid Imaging Located in the anterior neck between suprasternal notch and thyroid cartilage. Consists of 2 lobes approx 3-4 cm long. Isthmus connects lobes. Thyroid overlies trachea Highly vascular (superior/inferior thyroid arteries)

    10. Thyroid Imaging Thyroid imaging is one of the earliest NM procedures developed Based on physiological process of thyroid hormone production T-3(triiodothyronine) & T- 4(tetraiodothyronine)

    11. Thyroid Imaging T-3 and T-4 are products of iodine absorbed into the blood from digestion. Blood transports iodine in the form of iodide to the thyroid gland. Iodide is trapped by thyroid follicular cells. Process is called iodide pump.

    12. Thyroid Imaging Hormones produced in the thyroid are stored there until they are required by body. Thyroid controls many metabolic processes: growth and development, body temperature regulation, metabolism of proteins, lipids, carbohydrates, vitamins, and minerals.

    13. Thyroid Imaging Thyroid hormone production and secretion controlled by negative feedback. TSH (thyroid stimulating hormone) released by pituitary gland, regulates thyroid iodide uptake and release.

    14. Clinical Indications Evaluate gland structure to function Evaluate gland size and palpable nodules or masses. Identify ectopic thyroid tissue located from base of tongue to below sternum.

    15. Thyroid Imaging procedure Prior to dose administration patient should be questioned: previous thyroid surgery,thyroid symptoms, thyroid medications, recent radiographic procedures. Many medications, iodine containing foods, and radiographic procedures using iodinated contrast can affect radioiodine uptake.

    16. Thyroid Imaging procedure All females of chidbearing age should be questioned Lab values for thyroid hormones will aid in interpretation. Radiopharmaceuticals administered orally or intravenously Tc99m is tracer administered IV and imaging begins 15-30min PI.

    17. Thyroid Imaging Procedure I-123 sodium iodide is administered orally and imaged 3-4hrs or 16-24hrs.after administration I-131 sodium iodide is administered orally and imaged 6-24hrs after administration Patient placed supine with neck hyperextended.

    18. Thyroid Imaging procedure Pinhole or LEHR collimator used for imaging Images are acquired in the anterior and oblique projections Marker images acquired anteriorly at supersternal notch and over thyroid cartlidge. Ectopic thyroid tissue suspected an anterior view of mediastinum is obtained

    20. Thyroid Imaging Procedure Normal findings: >butterfly shaped structure with a uniform symmetric distribution of activity >right lobe slightly larger than left >isthmus not well defined >pyramidal (third lobe) may be visualized.

    21. Thyroid Imaging Procedure Abnormal findings: >enlarged thyroid gland >visualization of functioning and non-functioning thyroid nodules >functioning HOT nodules represent benign cysts or tumors >non-functioning COLD nodules represent carcinoma, benign adenoma, cysts, hematoma, inflammatory condotions.

    22. Thyroid Uptake Procedure If using I-123 or I-131 capsules a thyroid uptake is obtained Measures amount of radioactive iodide that is taken and retained within thyroid gland. Uptake at 2-6hrs measures iodine trapping Uptake at 24-48hrs measures rate of iodine is lost from gland

    23. Thyroid Uptake Procedure I-123 and I-131 in capsule or liquid form (most common capsule) Preferred thyroid uptake, possible with Tc99m. Patient preparation same as radioiodine thyroid imaging NPO and fasting 2hrs post administration Data (uptake) collected with thyroid uptake probe (sodium iodide crystal flat field collimator)

    24. Thyroid Uptake Procedure Thyroid gland counts are collected with patient in supine or seated (erect) position Neck is hyperextended, probe over centered between suprasternal notch and thyroid cartlidge.

    25. Thyroid Uptake Procedure Thyroid uptake calculations are obtained by Patient counts from the neck and patient background. Counts from standard (capsule) and room background 1min counts are obtained for each. Normal values= 4hrs 6%-18% 24hrs 10%-35%

    26. Radioiodine Whole-body Imaging Post thyroid-ectomy (carcinoma) whole body radioiodine imaging is acquired To identify remaining residual thyroid tissue or metastasis. I-131 sodium iodide most commonly used. 1-10mCi I-131 administered orally

    27. Radioiodine whole body Imaging Patient preparation similar to thyroid imaging Anterior and posterior images of body from head to mid-femur acquired. 24-48 hrs post administration Anatomical landmarks placed on images, activity seen in salivary glands, thyroid tissue remnants, stomach, esophagus, functioning metastasis.

    28. Parathyroid Imaging 4 parathyroid glands located on posterior aspect of poles of thyroid gland Produce and secrete parathyroid hormone (PTH) Responsible for regulating level and distribution of calcium and phosphorus.

    29. Parathyroid Imaging Imaging useful when primary hyperthyroidism is suspected. Tumor in one of the parathyroid glands or hyperplasia of all four glands lead to excess PTH to be secreted. PTH stimulates the removal of calcium from bones, affects nervous system, muscle contraction, etc. Treatment is surgical removal of hyperplastic gland or tumor

    30. Parathyroid Imaging Parathyroid imaging acquired with either dual phase or dual tracer technique: :dual phase Tc99m sestamibi 5-25 mCi is administered :localizes in both thyroid/parathyroid tissue : tracer washes out of normal thyroid tissue quicker than abnormal parathyroid tissue

    31. Parathyroid Imaging Imaging 10min PI and again 1.5hr-2.5hr PI is obtained Abnormal parathyroid demonstrates retention of tracer, becomes better visualized on delay images.

    32. Parathyroid Imaging Dual tracer technique: Tc99m or I-123 sodium iodide (distinguish normal thyroid tissue) Tc99m-sestamibi or thallium-201 (localizes in both thyroid and abnormal parathyroid tissue) Advantages/Disadvantages: :scatter high energy to low energy :length of images (pt.cooperation) :activity of each tracer/time required for I123 to localize.

    33. Parathyroid Imaging Both images are normalized, so counts per pixel are the same for both images. Tc99m/I-123 images are subtracted from Tc99m sestamibi/thallium-201 images. Final images reveal area of abnormal parathyroid.

    34. Parathyroid Imaging Dual phase techniques has several advantages: One injection and tracer (Tc99m sestemibi) No computer subtraction needed Radiation dose decreased to patient.


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