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 Table of Contents  
Year : 2022  |  Volume : 7  |  Issue : 2  |  Page : 77-81

Is 99mtechnetium (Pertechnetate) more efficient in clinical evaluation of thyroid lesions compared to 123iodine? A scoping review

1 Department of Radiological Sciences, King Khalid University, Abha, Saudi Arabia
2 Department of Diagnostic Radiology, College of Applied Medical Sciences, Jazan University, Saudi Arabia
3 Medical Research Center, Jazan University, Jazan, Saudi Arabia
4 Department of Radiological Sciences, College of Applied Medical Sciences, King Saud University, Riyadh, Saudi Arabia

Date of Submission18-Apr-2021
Date of Acceptance01-Dec-2021
Date of Web Publication27-Dec-2022

Correspondence Address:
Dr. Magbool Alelyani
Department of Radiological Sciences, King Khalid University, Abha 62529
Saudi Arabia
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/KKUJHS.KKUJHS_17_21

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Background: This research aims to find out which radiopharmaceutical is more efficient to evaluate thyroid lesions, such as hyperthyroidism, Graves' disease (GD), or even cold or hot thyroid nodule identification (is 99mtechnetium [99mTc] or 123iodine [123I] suitable in this case?). Materials and Methods: An extensive computerized search was done by the authors, revealing 61 studies in total. 49 studies were excluded for various reasons, so only 12 were eligible for inclusion in this review. Results: Majority of the studies suggested that the use of 99mTc over 123I. 99mTc is a suitable choice to evaluate thyroid disorders. However, 123I can be broadly used in assessing thyroid functions, detecting malignancy and causes of thyrotoxicosis, calculating therapeutic dosages of 131I, and identifying cold or hot lesions effectively due to its superior accumulation in thyroid. Conclusion: 99mTc is a nonphysiologic compound widely used to evaluate thyroid abnormalities, and it has a noticeably low biodistribution in the thyroid. On the other hand, 123I is an organic compound with excellent biodistribution that is used to gather further information on thyroid functions and susceptibility and prevalence of toxic adenoma, GD, and cold or hot thyroid nodule evaluation.

Keywords: 123Iodine, 99mtechnetium, Graves, hypothyroidism, thyroid nodules, thyrotoxicosis

How to cite this article:
Alelyani M, Alshehri M, Shubayr N, Alashban Y, Alshihri A. Is 99mtechnetium (Pertechnetate) more efficient in clinical evaluation of thyroid lesions compared to 123iodine? A scoping review. King Khalid Univ J Health Sci 2022;7:77-81

How to cite this URL:
Alelyani M, Alshehri M, Shubayr N, Alashban Y, Alshihri A. Is 99mtechnetium (Pertechnetate) more efficient in clinical evaluation of thyroid lesions compared to 123iodine? A scoping review. King Khalid Univ J Health Sci [serial online] 2022 [cited 2023 Jan 30];7:77-81. Available from: https://www.kkujhs.org/text.asp?2022/7/2/77/365754

  Introduction Top

The thyroid is an endocrine gland that secretes hormones directly into the bloodstream. Thyroxin (T4), triiodothyronine (T3), and calcitonin are produced by the thyroid. Iodine is an important factor in the synthesis of T4 and T3. T4 contains only four iodine atoms, and T3 contains only three iodine atoms.[1] In this way, the thyroid gland plays an important role in metabolic functions, such as controlling digestive functions, muscles, and the heart. Moreover, it has a profound impact on the growth of human body.

The thyroid is a unique structure shaped like a butterfly. Its anatomical position is between C5 and T1 anterior to the neck and inferior to the laryngeal prominence (commonly known as the Adam's apple). The thyroid can experience disorders such as hyperthyroidism, hypothyroidism, thyroiditis, thyroid nodules, and cancerous thyroid, which all present with different symptoms and should be investigated if suspected.

Thyroid disorders have been very common in recent years. For instance, when the thyroid gland is unable to adequately produce iodine, known as hypothyroidism, the most common cause is iodine deficiency,[2] whereas weight gain is a likely sign of thyroid hormone deficiency. Among diabetic population, few reports showed higher prevalence of thyroid disorders.[3] Other signs associated with hypothyroidism include increased diastolic blood pressure due to lower cardiac output.[4]

In 2009, over 37,000 people were diagnosed with thyroid cancer.[5] On the other hand, hyperthyroidism affects more women than men.[6] If the thyroid is over-active and produces an excess of iodine, hyperthyroidism occurs. This disorder causes Graves' disease (GD), which is considered as the main symptoms of hyperthyroidism. Weight loss, tachycardia, and fatigue are very common in elderly patient who suffer from hyperthyroidism.[7]

Globally, although thyroid disorders are common in the Saudi Arabia, the thyroid cancer ranked 2nd among female and 13th among male.[8] In 2006, there was an increased prevalence in number of people who suffered from thyroid cancer in the United States. However, in the early 1990s, the incidence rate of thyroid abnormalities is almost stable.[9] The incidence of thyroid cancer in Korean Society is increased in both males and females; the probability of thyroid cancer increases in those who aged between 40 and 50 years.[10]

The primary purpose of this research is to discover which radiopharmaceutical is most efficient for the assessment of patients who suffer from a wide range of thyroid disorders.

  Materials and Methods Top

As demonstrated in [Table 1] the authors searched electronic databases including Medscape, ScienceDirect, and PubMed yielding a total of 61 studies, 49 of which were excluded for various reasons and the remaining 12 were eligible for inclusion in this report. All these articles appearing in English, which were published from 1970 to 2020, were included in this research, as shown in [Figure 1].
Table 1: Studies inclusion and their findings alongside sample size regarding 99mtechnetium and 123iodine

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Figure 1: PRISMA diagram showing the searching, eligibility, and inclusion process

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We extended the search scope to include grey literature including authorized government websites such as the Saudi Ministry of Health, which contains unpublished articles in research engines. The following keywords were used to get accurate and relevant results: “'123Iodine' or '99mTc pertechnetate' or 'thyroid imaging' or 'thyroid uptake' or 'thyroid accumulation.'”

  Results Top

The vast majority of total searched articles showed that 99mtechnetium (99mTc) and 123iodine (123I) are relatively efficient in thyroid lesions assessment. However, 99mTc is preferable because of its short half-life and scan time. Its only disadvantage is its minimal thyroid accumulation due to its nontrapped and nonphysiologic properties, which will cause it to be expelled quickly from the thyroid.

On the other hand, 123I has a more significant thyroid accumulation due to its physiological properties, which make organized reaction with thyroid hormones. Before scan, the patient will have to wait up to 4 h to start the thyroid examination.

  Discussion Top

Comparison between 123-iodide and 99mtechnetium-pertechnetate

As illustrated in the [Table 2] according to Saha, 123I half-life is approximately 13.2 h. The 123I decays by electron capture and the abundance of gamma ray is nearly 83%.[22] In contrast, the half-life of 99mTc is 6 h, it decays by isomeric transition, and its gamma ray abundance is 90%. The absorbed dose is 13.00 rad/mCi for 123I, whereas 99mTc is 1300.00 rad/mCi. “The preferable dose of iodine is approximately 200–400 μCi, whereas 99mTc is 2–10 mCi.”[23]
Table 2: Important details regarding 123iodine and 99mtechnetium

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99mTc-pertechnetate is not organically bound and may not be suitable to be used to measure thyroid uptake by far. 99mTc is not organified or incorporated with thyroid hormones.[24] Moreover, it may provide poor details regarding cold or hot thyroid nodules. Since it is not organified, it will not be retained in the thyroid for longer period of time.[25] In contrast to 123I, it is trapped and organified by thyroid nodules and combined into thyroglobulin.[23] The iodine particles will interact with thyroid hormones and retained within thyroid longer. Therefore, 123I will efficiently accumulate and provide more details regarding thyroid condition.[26]

Energy and excretion routes of 123iodine and 99mtechnetium

When a patient is injected with 99mTc, the patient will be exposed to a radiation dose of approximately 140 KeV emitted by a tracer inside the patient body. If the patient was advised to take 123I, it will be administered orally and excreted by the urinary system. In addition, the patient will be exposed to a relatively high radiation dose of 159 KeV, which is larger than the 99mTc radiation dose. The excretion routes of both 99mTc and 123I are through the kidneys and exit of the body in the form of feces. Other advantages and disadvantages of both 99mTc and 123iodine are highlighted in [Table 3].
Table 3: Advantages and disadvantages of 123iodine and 99mtechnetium (pertechnetate) with administration method and estimated scan time

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Thyroid uptake test

This section raises the question of why do we need to see the level of thyroid uptake. “Thyroid uptake” is a term that describes the ability of the thyroid gland to absorb radioactive iodine. The thyroid will take up iodine from the blood to manufacture thyroid hormones (hence, the term “thyroid uptake”), and when large amounts of iodine accumulate in the thyroid, GD occurs.[27] Regarding patients who suffer from hyperthyroidism, their uptake percentages can help physicians determine the causes of the disorder.[23]

Hereditary factors are considered as risk factor of GD; however, the incidence of GD gets lower when you avoid smoking and follow a healthy lifestyle.[28] During pregnancy, hyperthyroidism gets abated, whereas it gets exacerbated after childbearing.[29] Thyroiditis, on the other hand, known as an inflammatory disease of thyroid that causes thyroid dysfunction has lower iodine uptake than GD.[30] Thyroid uptake level is a significant signal to identify thyroid diseases. Further details are found in [Table 4].
Table 4: Pathologies which affect the thyroid, along with levels of thyroid uptake determination[23]

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Four different groups of patients undertaken thyroid scan showed a different thyroid uptake according to type of pathology they suffer from. These pathologies are GD, toxic multinodular goiter (MNG), toxic adenoma (TA), and thyroiditis.

Group 1 shows that in patients who have already suffered GD, the level of iodine uptake is the highest compared to Groups 2, 3, and 4, with an uptake percentage of 80% to 90%. Another group of patients suffering from MNG display thyroid uptake of a mild/normal estimated percentage of iodine of less than 50%. On the other hand, in patients with TA, the percentage is nearly 50% with a normal/less-than-normal iodine uptake. In Group 4, if the patient has thyroiditis, the level of uptake in the thyroid is too low.[23]

The radiopharmaceutical in [Figure 2] is 123I, which demonstrates excellent biodistribution within the thyroid, thus providing an excellent diagnostic image quality. A physician can then easily decide which disease is present. Picture A shows a normal thyroid that did not absorb much iodine, unlike Picture B shows excessive iodine uptake by the thyroid, which is a significance sign of GD. Picture C shows toxic MNG, in which a large quantity of iodine is absorbed on the right side of the thyroid, whereas Picture D shows TA, during which iodine is mainly absorbed in the middle of thyroid.[23],[26]
Figure 2: 123Iodine showing different thyroid disorders[31]

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[Figure 3] demonstrates GD. As mentioned earlier, 99mTc is a nonorganified (nonphysiologic) compound, and it may not be accumulated, distributed, or absorbed by the thyroid properly. When comparing this image with Picture B in [Figure 2] of GD, the distribution of 99mTc is clearly not as extensive as that of 123I.[20],[23]
Figure 3: 99mTechnetium of enlarged thyroid[32]

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As shown in the [Figure 4] picture A, on the left, has a low total (99mTc) uptake of 0.49%, with its nonfunctioning area invisible in the image. In Picture B, 123I shows greater clarity, and its nonfunctioning region is clearly seen, with a total uptake of 19.5%.[23]
Figure 4: (a and b) Both images showing palpable nodules[33]

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  Conclusion Top

As shown in the [Table 5] 99mTc is widely available and affordable, and it is characterized by nontrapped and nonphysiologic properties. 99mTc can be quickly eliminated because of its insufficient accumulation in the thyroid, which provides little information on thyroid nodules. In contrast, 123I is trapped and organified by thyroid hormones, and it has excellent biodistribution. It also stays longer in the thyroid and produces better thyroid accumulation; despite its cost and long diagnostic examinations, it is nevertheless far more effective than 99mTc in evaluating and determining thyroid malfunctions and causes of hyperthyroidism.
Table 5: Accumulation of 99mtechnetium (pertechnetate) and 123iodine in thyroid scintigraphy

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Authors extend their appreciation to the College of Applied Medical Sciences Research Center and Deanship of Scientific Research at King Saud University for funding this project.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4]

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]


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