Endocrine System

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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
• gtpituitary gland (anterior/posterior)
• gtthyroid gland
• gtparathyroid gland
• gtislet cells of the pancreas
• gtadrenal glands (cortex/medulla)
• gtgonads (ovaries/testes)

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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

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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

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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.

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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.

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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.

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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.

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Adrenal Gland Imaging

• Metastases from Pheochromocytomas may be
  visualized in liver, bone, lymph nodes, heart,
  and lungs.

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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)

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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)

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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

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Thyroid Imaging Procedure

• Normal findings
• gtbutterfly shaped structure with a uniform
  symmetric distribution of activity
• gtright lobe slightly larger than left
• gtisthmus not well defined
• gtpyramidal (third lobe) may be visualized.

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Thyroid Imaging Procedure

• Abnormal findings
• gtenlarged thyroid gland
• gtvisualization of functioning and
  non-functioning thyroid nodules
• gtfunctioning HOT nodules represent benign
  cysts or tumors
• gtnon-functioning COLD nodules represent
  carcinoma, benign adenoma, cysts, hematoma,
  inflammatory condotions.

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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

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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)

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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.

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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

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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

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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.

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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.

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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

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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

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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.

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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.

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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.

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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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