Transcript Ideal Radionuclide

Radiology and Endocrinology
ANATOMY
• Radiography
• Ultrasound
• CT
• MRI
FUNCTION
• Radionuclide
Imaging
- Scintigraphy
- PET
Radionuclide Imaging
• Images metabolic pathways
• Pharmaceutical which mimics a
component of a normal metabolic
pathway is administered to the patient
• Pharmaceutical radiolabelled so that its
distribution in the patient can be
visualised with a gamma camera
Ideal Radionuclide
• emits gamma radiation at suitable energy
for detection with a gamma camera
(60 - 400 kev, ideal 150 kev)
• should not emit alpha or beta radiation
• half life similar to length of test
• cheap
• readily available
Ideal radiopharmaceutical
• cheap and readily available
• radionuclide easily incorporated without
altering biological behaviour
• radiopharmaceutical easy to prepare
• localises only in organ of interest
• t1/2 of elimination from body similar to
duration of test
Thyroid - radiography
• Little role
• Thyroid mass diagnosed incidentally on
chest radiograph
• Thoracic inlet views may demonstrate
tracheal compression
Thyroid - ultrasound
• High resolution (5 - 10 MHz)
• Confirms - mass is thyroid
cystic or solid
single or multiple
• cannot distinguish solid carcinoma from
solid dominant nodule
• Not useful in hyperthyroidism
Thyroid - CT/MRI
• Not as good as US at resolving lesions
within the thyroid
• Best tests for assessing mediastinal
disease
• CT better than MRI for calcification
• MRI better than CT for distinguishing
between fibrosis and residual tumour
Thyroid - scintigraphy
99m PERTECHNETATE
Trapped but not organified
Competes with iodide for uptake
Cheap and readily available
IODINE (123I or 131 I)
Trapped and organified
Better for retrosternal goitres
Expensive, cyclotron generated
RECENT (10 days) IODINE CONTRAST
BLOCKS UPTAKE
Thyroid scintigraphy
99m Tc
123 NaI
ADMIN
iv
po/iv
PATIENT
PREP
withdraw thyroid Rx
avoid high Iodine foods
IMAGING
15 min pi
1-2hr pi
24 hr po
Hyperthyroidism
RN uptake
1. Thyroid gland (>95%)
Toxic nodular goitre
Diffuse toxic goitre (Graves)
Thyroiditis
2. Exogenous T3/4/iodine
Iatrogenic
Iodine - induced
(XRay contrast, amiodarone)
Thyroid nodules
Risk of malignancy
Overall
10%
US - cystic
0.3 - 10%
US - solid
????
RNI - cold
16%
RNI - hot
4%
First line investigation: Cytology +/- US
RNI in thyroid disease
• Investigation of hyperthyroidism
• Location of ectopic thyroid tissue
(congenital hypothyroidism, retrosternal
goitre)
• Little role in thyroid nodules
ry
1 Hyperparathyroidism
Adenomas
Hyperplasia
Carcinoma
Type
%
Single
Chief cell
Clear cell
80
15
1
4
RN parathyroid imaging
99mTc
/ 201Tl
subtraction scans
99mTc-MIBI
early/late scans
False positives: thyroid pathology
False negatives: parathyroid hyperplasia
Both good for ectopic parathyroids
Parathyroid imaging
• US
not good at finding ectopic glands
• CT
Contrast
Surgical artifacts
• MRI Good for localisation and ectopic
glands
Imaging parathyroids
Uncomplicated 1ry hyperparathyroidsim
90 -95% surgical success rate without
imaging
Recurrent/persistent hyperparathyroidism
surgical success rate without imaging -50%
with imaging - 90%
(combined RNI + MRI)
Adrenal glands
Cortex
aldosterone
cortisol
adrenal androgens
Medulla
adrenalin
Adrenal glands
• AXR - may show calcification
• US - large masses only (unless neonatal)
• CT - can detect small lesions
- cannot distinguish metastases
from non-functioning adenomas
• MRI - small lesions
- may distinguish mets from
non-functioning adenomas
Adrenal cortical RNI
• Radiolabelled cholesterol esters
(75 Seleno-methylnorcholesterol,
131 I - 6B iodomethyl-19-norcholesterol)
• Image at 4 and 7 days
• > 50% difference in activity between
sides is abnormal
RNI in Cushings syndrome
ACTH-dependent CS
pituitary/ectopic
ACTH -independent CS
bilat nodular hyperplasia
adrenocortical adenoma
bilat
Adrenocortical carcinoma
bilat
bilat
uni
Cushings syndrome
Diagnosis
- biochemistry
Localisation - CT/MRI
for
1. Pituitary ACTH-dependent
2. Ectopic ACTH-dependant
3. ACTH - independant
RNI not usually necessary
RNI and Cushings syndrome
Used for
1. Finding residual functioning adrenal
remnants if recurrent disease after prior
bilateral adrenalectomy
2. Somatostatin receptor scanning for
ectopic ACTH from small bronchial
carcinoid tumours
Primary aldosteronism
• small tumours may not be seen with
CT/MRI
• RNI + dexamethasone suppression can
find tumours < 1cm
• Adrenal visualisation before 5 days is
abnormal (bilateral/unilateral)
Adrenal medullary RNI
Phaeochromocytoma
Paraganglioma
Neuroblastoma
Ganglioneuroblastoma
Ganglioneuroma
Adrenal medullary RNI
• Metaiodobenzylguanidine (MIBG)
- localises in catecholamine storage
vesicles of adrenergic nerve endings
- 123 I or 131 I
• somatostatin receptor imaging
111 In octreotide
MIBG
•
•
•
•
phaeochromocytomas (95% sensitivity)
neuroblastoma
(80 - 90% sens)
carcinoid
medullary thyroid carcinoma
(MEN syndromes)
Phaeochromocytomas
10%
malignant
bilateral
extra- adrenal
paediatric
Phaeochromocytomas
Diagnosis - biochemistry
Localisation
CT if > 2cm
RNI to exclude - small tumours
- bilateral adrenal
- multifocal
- metastases
‘Incidentalomas’
Incidental adrenal mass in patients
undergoing abdominal imaging (2%)
Q. Is it functioning?
Is it benign or malignant?
Functioning ‘incidentalomas’
Diagnosis
Clinical features
Biochmistry
Confirmation
RNI
Non-functioning
Non-functioning adenoma vs. metastasis
• CT using attenuation values
• MRI - chemical shift imaging
Radiology and Endocrinology
Localisation
not
Diagnosis
IMAGING
and the
ENDOCRINE SYSTEM