parathyroid scintigraphy

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Technetium-99m Tetrofosmin parathyroid scintigraphy in hyperparathyroidism: A Comparative study with Technetium -99mSestamibi Scintigraphy

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Technetium-99m Tetrofosmin parathyroid scintigraphy in hyperparathyroidism: A Comparative study with Technetium -99mSestamibi Scintigraphy : 

Technetium-99m Tetrofosmin parathyroid scintigraphy in hyperparathyroidism: A Comparative study with Technetium -99mSestamibi Scintigraphy Dr Anjali Jain, Dr (Col)Sudhir Tripathi, Dr Ishita Sen, Sir Ganga Ram Hospital New Delhi

Slide 2: 

Objective: To compare Tc-99m sestamibi scintigraphy with Tc-99m tetrofosmin scintigraphy in imaging abnormal parathyroid glands. To compare Tc-99m tetrofosmin/pertechnetate subtraction scintigraphy (Dual tracer) with dual phase imaging.

Study Design : 

Study Design Prospective study: Patients of suspected hyperparathyroidism in the department of Nuclear medicine at Sir Ganga Ram hospital, New Delhi (July 2005-November2007) Inclusion criteria: Patients with primary, secondary and tertiary hyperparathyroidism Patients with suspicious parathyroid mass on conventional imaging Exclusion criteria: Pregnant and lactating women Recent nuclear medicine procedure

Material and Methods : 

Material and Methods Two approaches: Dual tracer: 1. 3 mci of pertechnetate (Thyroid agent) is given iv 2. In the same position 20 mci of 99m Tc sestamibi given iv and images are acquired. 3. With the appropriate computer software the two images are subtracted to get the adenomatous tissue. 4. On a separate day, same protocol can be followed with Tc-99m tetrosmin.

Slide 5: 

Dual phase: Along with the early images acquired in the earlier protocol, delayed images are acquired at 2 hours for both sestamibi and tetrofosmin Image acquisition Images acquired by dual head gamma camera, high resolution parallel hole collimator, 20% window at 140 KeV photopeak. Planar static images of the neck and mediastinum are acquired at 10 min & 2hrs for both the agents. Isotime imaging for 10 minutes SPECT imaging when required.

Principle of imaging : 

Principle of imaging Pertechnetate is taken up by the thyroid tissue only Dual Tracer: Mitochondrial agents (Sestambi and tetrofosmin) are taken up by the thyroid and the abnormal parathyroid glands Subtraction of the two images will give us the final adenomatous tissue Dual phase: Tracer is taken up by the thyroid and abnormal parathyroid on early images. On delayed imaging at 2 hours, there is wash out of the tracer from the thyroid tissue and retention in the adenoma so that it stands out clear to be visualised

Results : 

Results Sensitivity of sestamibi-94.1% Sensitivity of tetrofosmin-79.4% Sensitivity of sestamibi/pertechnetate subtraction-97% Sensitivity of Tetrofosmin/pertechnetate subtraction -94%

Case I : 

Case I 26 yrs/M Presented with left arm swelling & pain x 1 month Left patellar fracture x 2 yr back B/L shoulder dislocation

Investigations: : 

Investigations: X ray left arm: Multiple cystic lesion involving humerus bone S. Calcium – 11 mg/dl S. Phosphorus – 3.30 mg/dl Alk. Phos. – 378 IU/l PTH – 772.32 pg/ml Total 24 urinary calcium level – WNL USG neck - normal

Case II : 

Case II 18 yrs male Presented with pancreatitis and pancreatic pseudocyst. S.Calcium-12.7 mg/dl S. Phoshate-2.5 mg/dl S. PTH-534pg/ml

Case III : 

Case III 53 yrs Female Presented with backache and bodyache x 1 yr Past history of thyroid surgery in 1992 for cold nodule, Presently on Eltroxin S. Calcium- 12.5 mg/dl S. Phosphate – 2.9 mg/dl S. PTH – 346 pg/ml USG neck – No evidence of parathyroid adenoma

Case IV : 

Case IV 31 yr female Presented with backache since 1 month History of fracture Rt humerus after trivial trauma S. Calcium-11.4 mg/dl S.phosphorus-1.6mg/dl S.PTH – 101.23pg/ml MRI Neck and Thorax- ? left lower adenoma

Slide 16: 

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Case V : 

Case V 65 years female History of rheumatoid arthritis and osteoporosis Parathormone -84.7 pg/ml S.calcium- 9.3 mg/dl S. Phosphorus- 3.3 mg/dl

Detailed analysis of a subgroup : 

Detailed analysis of a subgroup Primary hyperparathyroid Sample size -38 Male -15 Female-23 Clinical Presentation Bone Pain -18 Fractures- --------- Asymtomatic-9 Renal calculus-6 Others-4

Sensitivity and Specificity of SestaMIBI and Tetrofosmin : 

Sensitivity and Specificity of SestaMIBI and Tetrofosmin Tc-99m Sestamibi Sample size,(n)= 38 True Positive= 32 False Negative= 2 False Positive -0 True negative-4 Tc-99m Tetrofosmin Sample size,(n)= 38 True Positive= 27 False Negative= 7 False Positive -0 True negative-4

Sensitivity and Specificity of subtraction imaging : 

Sensitivity and Specificity of subtraction imaging Sestamibi/pertechnetate subtraction Sample size,(n)= 38 True Positive= 33 False Negative= 1 False Positive -0 True negative-4 Tetrofosmin/pertechnetate subtraction Sample size,(n)= 38 True Positive= 32 False Negative= 2 False Positive -0 True negative-4

Specificity : 

Specificity Tc99m Sestamibi and sestamibi/pertechnetate subtraction Sample size,(n)= 38 True Negative -4 False Positive -0 Tc 99 m Tetrofosmin and tetrofosmin/pertechnetate subtraction. Sample size,(n)= 38 True Negative- 4 False Positive -0

Conclusion : 

Conclusion Tc 99m SestaMIBI is a better agent than Tc 99m Tetrofosmin for imaging primary hyperparathyroidism Image quality of Tetrofosmin is poor making the interpretation of the adenoma difficult Uptake of Tetrofosmin in the adenomatous tissue is poor in the early image Delayed images show early washout making its visualization faint and difficult Washout from the thyroid tissue is poor in the delayed image, so that the adenomatous tissue does not stand out separate from the thyroid.

Slide 27: 

Subtraction imaging is very useful for correct interpretation of the adenoma especially in associated thyroid disorders. More sensitive Imaging time is less

Review of literature : 

Review of literature

Hyperparathyroidism : 

Hyperparathyroidism Primary ( PTH, normal or Ca 2+ ) Adenoma 90% Hyperplasia 10% Carcinoma < 0.1% Secondary ( PTH appropriate to low Ca 2+ ) Chronic Renal Failure Vitamin D Deficiency Tertiary Continued excess PTH secretion following prolonged secondary hyperparathyroidism.

Signs/Symtoms : 

Signs/Symtoms Asymptomatic (mild, < 2.99) “Bones, stones, abdominal groans, psychic moans”

Investigations : 

Investigations Imaging should be performed only after the diagnosis of primary HPT is established by biochemical findings In patients with primary HPT who have not undergone previous neck surgery, preoperative localization imaging is controversial Radiological localization of hyperfunctioning PTH tissue was reserved for re-exploration surgery. Intractable secondary and tertiary hyperparathyroidism where surgical management is planned, pre operative parathyroid scan may be done to localize functioning ectopic parathyroid glands.

Indications for Imaging : 

Indications for Imaging Shaha et al describe the following patients in whom preoperative imaging studies are warranted: Asymptomatic patients with mild hypercalcaemia. Patients in hypercalcaemic crisis in whom urgent diagnosis is needed Patients with associated malignancies Obese patients with short necks

Slide 33: 

Patients with cervical spinal problems in whom neck extension may be difficult Patients with associated palpable thyroid abnormalities High-risk patients in whom operative time is crucial or in whom local anesthesia must be used

Imaging Modalities : 

Imaging Modalities Sensitivity of US in detecting parathyroid adenomas is 55-83%. US is especially limited in the mediastinum; in this area, its sensitivity is as low as 29% The sensitivity of CT in detecting parathyroid adenomas is 40-90%. The sensitivity for MRI is 57-100%. MRI is especially useful in detecting ectopic mediastinal glands, with reported sensitivities of 88-96%. Sensitivity of the nuclear medicine techniques in detecting parathyroid adenomas is 90-100%.

Nuclear scintigraphy : 

Nuclear scintigraphy With the advent of MIRP (Minimally invasive radioguided parathyroidectomy) parathyroid scintigraphy is now recommended not only in persistent or recurrent hyperparathyroidism but also in every case prior to first surgery. Radiopharmaceuticals used are Tl-201-Tc99m Pertechnetate subtraction 99m Tc Sestamibi 99m Tc Tetrofosmin.

Radiopharmaceuticals : 

Radiopharmaceuticals .1. Tl-201-Tc99m Pertechnetate subtraction scintigraphy is not used now 2.Tc Sestamibi (2-methoxy isobutyl isonitrile) is now considered the best preoperative localising modality for detection of parathyroid adenomas Its favourable characteristics are Optimal photon energy (140 Kev) Short Half life (6 hours) Low radiation

Tc 99m Tetrofosmin (Trans –dioxo-bis complex)- : 

Tc 99m Tetrofosmin (Trans –dioxo-bis complex)- Mitochondrial agent similar to sestaMIBI Low effective dose of absorbed radiation Preparation does not requires heating

Tc 99m tetrofosmin in parathyroid imaging.. Diff opinions : 

Tc 99m tetrofosmin in parathyroid imaging.. Diff opinions Masatoshi ishibashi et al .. SestaMIBI and Tetrofosmin both have equal sensitivity for localization of abnormal parathyroid glands. The sensitivity of these tracers is high compared to USG or MRI Froberg A.C. et al.. Tc 99m Tetrofosmin is less suitable for double phase parathyroid scintigraphy because the increase in lesion to thyroid ratio in delayed images seen with sestaMIBI was not seen with Tetrofosmin Nowak B. et al.. Tc 99m Tetrofosmin is a suitable agent for parathyroid imaging only if used together with Tc 99m pertechnetate. It seems to lack the differential wash out characteristics between thyroid and parathyroid as seen with MIBI

Slide 39: 

Tc 99m Tetrofosmin may be a suitable tracer for imaging abnormal parathyroid glands, but the early images are better than the delayed ones. Also Tetrofosmin clears more slowly from the normal thyroid gland compared to sestaMIBI Tetrofosmin has the same success rate as sestaMIBI for detection of adenomas on early images. In contrast to MIBI delayed imaging has no diagnostic impact.

Dual tracer imaging : 

Dual tracer imaging Presently a single tracer (Dual phase) imaging early and late acquisitions is now widely used Concomitant thyroid selective imaging is essential when there is underlying thyroid disease or a history of neck surgery or occasionally can uncover a subtle lesion However many investigators found that the difference in kinetics of Tc 99 m sestaMIBI could not be observed in all adenomas and hence, consider thyroid scintigraphy to be mandatory.

Take home message : 

Take home message Tc 99 m sestaMIBI dual tracer technique with a thyroid agent (pertechnetate) along with the delayed images should be the technique of choice Tetrofosmin is not as good as sestaMIBI

Thank You! : 

Thank You!

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