Department of Nuclear Medicine, University Hospital Essen, University of Duisburg-Essen, Hufelandstrasse 55, 45122, Essen, Germany.
Eur J Nucl Med Mol Imaging. 2011 Oct;38(10):1862-8. doi: 10.1007/s00259-011-1866-1. Epub 2011 Jul 8.
This study compares intrinsically coregistered 124I positron emission tomography (PET) and CT (PET/CT) and software coregistered 124I PET and MRI (PET/MRI) images for the diagnosis and dosimetry of thyroid remnant tissues and lymph node metastases in patients with differentiated thyroid carcinoma (DTC).
After thyroidectomy, 33 high-risk DTC patients (stage III or higher) received 124I PET/CT dosimetry prior to radioiodine therapy to estimate the absorbed dose to lesions and subsequently underwent a contrast-enhanced MRI examination of the neck. Images were evaluated by two experienced nuclear medicine physicians and two radiologists to identify the lesions and to categorize their presumable provenience, i.e. thyroid remnant tissue (TT), lymph node metastasis (LN) and inconclusive tissue. The categorization and dosimetry of lesions was initially performed with PET images alone (PET only). Subsequently lesions were reassessed including the CT and MRI data.
The analyses were performed on a patient and on a lesion basis. Patient-based analyses showed that 26 of 33 (79%) patients had at least one lesion categorized as TT on PET only. Of these patients, 11 (42%) and 16 (62%) had a morphological correlate on CT and MRI, respectively, in at least one TT PET lesion. Twelve patients (36%) had at least one lesion classified as LN on PET only. Nine (75%) of these patients had a morphological correlate on both CT and MRI in at least one LN PET lesion. Ten patients (30%) showed at least one lesion on PET only classified as inconclusive. The classification was changed to a clear classification in two patients (two LN) by CT and in four (two TT, two LN) patients by MRI. Lesion-based analyses (n=105 PET positive lesions) resulted in categorization as TT in 61 cases (58%), 16 (26%) of which had a morphological correlate on CT and 33 (54%) on MRI. A total of 29 lesions (27%) were classified as LN on PET, 18 (62%) of which had a morphological correlate on CT and 24 (83%) on MRI. In 16 lesions (15%) PET alone allowed no definite categorization. Categorization was achieved with the aid of CT and MRI, respectively, in five (one TT, four LN) and in six (two TT, four LN) lesions. In direct comparison, 23 lesions were not discernible on CT but clearly visible on MRI, 15 of which were smaller than 10 mm and about two thirds were classified as TT. Redoing dosimetry based on the volume information from MRI for these small lesions would have changed the initial therapy regime in five patients. These patients would have received (131)I therapy with standardized activities of 3.7 GBq or 7.4 GBq instead of activities higher than 10 GBq and would have benefited from reduced radiation exposure.
PET/MRI is superior to PET/CT in terms of tracing back a PET focus to a morphological correlate. For this reason PET/MRI enhances diagnostic certainty for lesions<10 mm and improves pretherapeutic lesion dosimetry in DTC.
本研究旨在比较碘-124 正电子发射断层扫描（PET）与 CT （PET/CT）固有配准以及碘-124 PET 与 MRI（PET/MRI）软件配准，以诊断和计量分化型甲状腺癌（DTC）患者的甲状腺残留组织和淋巴结转移。
甲状腺切除术后，33 例高危 DTC 患者（III 期或以上）在放射性碘治疗前接受 124I PET/CT 剂量测定，以估计病变的吸收剂量，随后进行颈部增强 MRI 检查。两名有经验的核医学医师和两名放射科医师对图像进行评估，以识别病变并对其假定来源进行分类，即甲状腺残留组织（TT）、淋巴结转移（LN）和不确定组织。最初仅使用 PET 图像进行病变的分类和剂量测定（仅 PET）。随后，在包括 CT 和 MRI 数据的情况下重新评估病变。
对患者和病变进行了分析。基于患者的分析显示，33 例患者中有 26 例（79%）至少有一个病变在仅 PET 上被归类为 TT。在这些患者中，11 例（42%）和 16 例（62%）在至少一个 TT PET 病变中 CT 和 MRI 有形态学相关性。12 例患者（36%）至少有一个病变在仅 PET 上被归类为 LN。在至少一个 LN PET 病变中，这些患者中有 9 例（75%）CT 和 MRI 均有形态学相关性。10 例患者（30%）在仅 PET 上至少有一个病变被归类为不确定。通过 CT，2 例（2 例 LN）和 MRI，4 例（2 例 TT，2 例 LN），将分类改为明确分类。基于病变的分析（n=105 个 PET 阳性病变）导致 61 例（58%）分类为 TT，其中 16 例（26%）在 CT 上有形态学相关性，33 例（54%）在 MRI 上有形态学相关性。共有 29 个病变（27%）在 PET 上被归类为 LN，其中 18 个（62%）在 CT 上有形态学相关性，24 个（83%）在 MRI 上有形态学相关性。在 16 个病变（15%）中，仅 PET 无法进行明确分类。分别通过 CT 和 MRI 对 5 个（1 个 TT，4 个 LN）和 6 个（2 个 TT，4 个 LN）病变进行了分类。直接比较，23 个病变在 CT 上不可见，但在 MRI 上清晰可见，其中 15 个病变小于 10 毫米，约三分之二被归类为 TT。对于这些小病变，根据 MRI 的体积信息重新进行剂量测定，将改变 5 名患者的初始治疗方案。这些患者将接受（131）I 治疗，标准化活度为 3.7GBq 或 7.4GBq，而不是高于 10GBq 的活度，并将受益于减少辐射暴露。
与 PET/CT 相比，PET/MRI 在追踪 PET 焦点到形态学相关性方面更具优势。因此，PET/MRI 提高了<10mm 病变的诊断确定性，并改善了 DTC 的术前病变剂量测定。
