Optimization of the protocols for the use of contrast agents in PET/CT studies. / Optimización de los protocolos y del uso de contrastes en tomografía computarizada de los equipos de tomografía por emisión de positrones.

The introduction of PET/CT scanners in clinical practice in 1998 has improved care for oncologic patients throughout the clinical pathway, from the initial diagnosis of disease through the evaluation of the response to treatment to screening for possible recurrence. The CT component of a PET/CT study is used to correct the attenuation of PET studies; CT also provides anatomic information about the distribution of the radiotracer. CT is especially useful in situations where PET alone can lead to false positives and false negatives, and CT thereby improves the diagnostic performance of PET. The use of intravenous or oral contrast agents and optimal CT protocols have improved the detection and characterization of lesions. However, there are circumstances in which the systematic use of contrast agents is not justified. The standard acquisition in PET/CT scanners is the whole body protocol, but this can lead to artifacts due to the position of patients and respiratory movements between the CT and PET acquisitions. This article discusses these aspects from a constructive perspective with the aim of maximizing the diagnostic potential of PET/CT and providing better care for patients.

18F-FDG positron emission tomography in oncology: main indications. / Tomografía por emisión de positrones con 18F-FDG en oncología: principales indicaciones.

The development of molecular and functional imaging with new imaging techniques such as computed tomography, magnetic resonance imaging, and positron emission tomography (PET) among others, has greatly improved the detection of tumors, tumor staging, and the detection of possible recurrences. Furthermore, the combination of these different imaging modalities and the continual development of radiotracers for PET have advanced our understanding and knowledge of the different pathophysiological processes in cancer, thereby helping to make treatment more efficacious, improving patients' quality of life, and increasing survival. PET is one of the imaging techniques that has attracted the most interest in recent years for its diagnostic capabilities. Its ability to anatomically locate pathologic foci of metabolic activity has revolutionized the detection and staging of many tumors, exponentially broadening its potential indications not only in oncology but also in other fields such as cardiology, neurology, and inflammatory and infectious diseases.

N staging of lung cancer patients with PET/MRI using a three-segment model attenuation correction algorithm: initial experience.

OBJECTIVES: Evaluate the performance of PET/MRI at tissue interfaces with different attenuation values for detecting lymph node (LN) metastases and for accurately measuring maximum standardised uptake values (SUVmax) in lung cancer patients. MATERIALS AND METHOD: Eleven patients underwent PET/CT and PET/MRI for staging, restaging or follow-up of suspected or known lung cancer. Four experienced readers determined the N stage of the patients for each imaging method in a randomised blinded way. Concerning metastases, SUVmax of FDG-avid LNs were measured in PET/CT and PET/MRI in all patients. A standard of reference was created with a fifth experienced independent reader in combination with a chart review. Results were analysed to determine interobserver agreement, SUVmax correlation between CT and MRI (three-segment model) attenuation correction and diagnostic performance of the two techniques. RESULTS: Overall interobserver agreement was high (κ = 0.86) for PET/CT and substantial (κ = 0.70) for PET/MRI. SUVmax showed strong positive correlation (Spearman's correlation coefficient = 0.93, P < 0.001) between the two techniques. Diagnostic performance of PET/MRI was slightly inferior to that of PET/CT, without statistical significance (P > 0.05). CONCLUSIONS: PET/MRI using three-segment model attenuation correction for LN staging in lung cancer shows a strong parallel to PET/CT in terms of SUVmax, interobserver agreement and diagnostic performance. KEY POINTS: •F18-FDG PET/MRI shows similar performance to F18-FDG PET/CT in lung cancer N staging. •PET/MRI has substantial interobserver agreement in N staging. •A three-segment model attenuation correction is reliable for assessing the mediastinum.

Update on iodine-refractory differentiated thyroid carcinoma.

Radioiodine therapy represents a fundamental pillar in the routine adjuvant therapy of patients with high-risk differentiated thyroid carcinoma. However, a non-negligible percentage of these patients will develop iodine refractoriness, showing a worse prognosis, as well a lower survival, which demonstrates a clear need to explore different therapeutic approaches. Iodine refractory patient treatment continues to be a challenge, currently having different novel therapeutic options that should be known by the different specialties related to differentiated thyroid carcinoma (DTC). The aim of this work is to review iodine refractory thyroid carcinoma treatment, focusing especially on the definition of iodine refractoriness, highlighting its importance due to its high mortality, and introducing the different therapeutic options available for these patients.

Immunotherapy, cancer and PET. / Inmunoterapia, cáncer y PET.

The treatment of cancer by immunotherapy has been a revolution, as it is the first strategy that manages to control the disease for prolonged periods of time. Its efficacy is associated with different imaging response patterns and the appearance of new toxicities. We would highlight two patterns of tumour response: pseudoprogression, or growth of tumour lesions after the start of immunotherapy treatment, followed by a significant reduction in lesions, and hyperprogression, acceleration of tumour progression and metastasis early after the start of treatment. The emergence of such patterns has generated new metabolic response criteria, such as PECRIT, PERCIMT, imPERCIST and IPERCIST. Of particular interest are the new immunoPET-specific biomarkers, as they allow the identification of patients presenting the tumour target and are useful for predicting response to immunotherapy.

A multidisciplinary consensus on the morphological and functional responses to immunotherapy treatment.

The implementation of immunotherapy has radically changed the treatment of oncological patients. Currently, immunotherapy is indicated in the treatment of patients with head and neck tumors, melanoma, lung cancer, bladder tumors, colon cancer, cervical cancer, breast cancer, Merkel cell carcinoma, liver cancer, leukemia and lymphomas. However, its efficacy is restricted to a limited number of cases. The challenge is, therefore, to identify which subset of patients would benefit from immunotherapy. To this end, the establishment of immunotherapy response criteria and predictive and prognostic biomarkers is of paramount interest. In this report, a group of experts of the Spanish Society of Medical Oncology (SEOM), the Spanish Society of Medical Radiology (SERAM), and Spanish Society of Nuclear Medicine and Molecular Imaging (SEMNIM) provide an up-to-date review and a consensus guide on these issues.

Study of the adrenergic heart innervation with iodine 123-metaiodobenzylguanidine in heart failure before transplantation.

BACKGROUND: The incidence and prevalence of heart failure (HF) are constantly increasing. Heart failure depends on pump failure, inflammatory tracers, and the neurohormonal system. At advanced stages, the only treatment is heart transplantation (HT). We studied myocardial innervation in patients before HT. MATERIALS AND METHODS: The study included 15 patients (11 men and 4 women; age range, 18-69 years) with a diagnosis of New York Heart Association class III-IV or IV HF. Planar thoracic images were obtained, at 15 minutes and 4 hours after injection of 10 mCi of iodine 123-metaiodobenzylguanidine ((123)I-MIBG). Adrenal activity was measured quantitatively using a heart-to-mediastinum count ratio and a myocardial washout rate. Pathologic results were considered if heart-to-mediastinum count ratio was less than 1.8 and washout rate was more than 35%. RESULTS: The qualitative analysis revealed decreased (123)I-MIBG myocardial uptake in all patients. Using the quantitative scale, patients were classified into four groups, as follows: group 1, physiologic innervation, no patients; group 2, mild myocardial adrenergic involvement, one patient (6.7%); group 3, moderate myocardial adrenergic involvement, five patients (33.3%); and group 4, severe myocardial adrenergic involvement, 9 patients (60%). The washout rate was pathologic in 11 of the 15 patients (73.3%). CONCLUSIONS: Scintigraphy using (123)I-MIBG is a useful method to evaluate prognosis in patients with advanced HF and can be used to assess transplantation priorities. It will be necessary to study a larger number of patients to confirm these findings.

A multidisciplinary consensus on the morphological and functional responses to immunotherapy treatment

The implementation of immunotherapy has radically changed the treatment of oncological patients. Currently, immunotherapy is indicated in the treatment of patients with head and neck tumors, melanoma, lung cancer, bladder tumors, colon cancer, cervical cancer, breast cancer, Merkel cell carcinoma, liver cancer, leukemia and lymphomas. However, its efficacy is restricted to a limited number of cases. The challenge is, therefore, to identify which subset of patients would benefit from immunotherapy. To this end, the establishment of immunotherapy response criteria and predictive and prognostic biomarkers is of paramount interest. In this report, a group of experts of the Spanish Society of Medical Oncology (SEOM), the Spanish Society of Medical Radiology (SERAM), and Spanish Society of Nuclear Medicine and Molecular Imaging (SEMNIM) provide an up-to-date review and a consensus guide on these issues (AU)

Qualitative and quantitative performance of ¹8F-FDG-PET/MRI versus ¹8F-FDG-PET/CT in patients with head and neck cancer.

BACKGROUND AND PURPOSE: MR imaging and PET/CT are integrated in the work-up of head and neck cancer patients. The hybrid imaging technology (18)F-FDG-PET/MR imaging combining morphological and functional information might be attractive in this patient population. The aim of the study was to compare whole-body (18)F-FDG-PET/MR imaging and (18)F-FDG-PET/CT in patients with head and neck cancer, both qualitatively in terms of lymph node and distant metastases detection and quantitatively in terms of standardized uptake values measured in (18)F-FDG-avid lesions. MATERIALS AND METHODS: Fourteen patients with head and neck cancer underwent both whole-body PET/CT and PET/MR imaging after a single injection of (18)F-FDG. Two groups of readers counted the number of lesions on PET/CT and PET/MR imaging scans. A consensus reading was performed in those cases in which the groups disagreed. Quantitative standardized uptake value measurements were performed by placing spheric ROIs over the lesions in 3 different planes. Weighted and unweighted κ statistics, correlation analysis, and the Wilcoxon signed rank test were used for statistical analysis. RESULTS: κ statistics for the number of head and neck lesion lesions counted (pooled across regions) revealed interreader agreement between groups 1 and 2 of 0.47 and 0.56, respectively. Intrareader agreement was 0.67 and 0.63. The consensus reading provided an intrareader agreement of 0.63. For the presence or absence of metastasis, interreader agreement was 0.85 and 0.70. The consensus reading provided an intrareader agreement of 0.72. The correlations between the maximum standardized uptake value in (18)F-FDG-PET/MR imaging and (18)F-FDG-PET/CT for primary tumors and lymph node and metastatic lesions were very high (Spearman r = 1.00, 0.93, and 0.92, respectively). CONCLUSIONS: In patients with head and neck cancer, (18)F-FDG-PET/MR imaging and (18)F-FDG-PET/CT provide comparable results in the detection of lymph node and distant metastases. Standardized uptake values derived from (18)F-FDG-PET/MR imaging can be used reliably in this patient population.

Recurrent and metastatic breast cancer PET, PET/CT, PET/MRI: FDG and new biomarkers.

Primary breast cancer often displays only moderately increased glucose metabolism resulting in a low sensitivity of positron emission tomography (PET) using [F-18]fluorodeoxyglucose (FDG) in detecting small breast carcinomas, locoregional micrometastases and non-enlarged tumor infiltrated lymphnodes. In contrast, distant breast cancer metastases are generally characterized by significantly increased metabolic activity compared to normal tissue. Therefore, FDG-PET provides accurate diagnostic information as a whole body imaging modality in staging of breast cancer patients. The metabolic information from FDG-PET/CT is often more sensitive than conventional imaging for the detection of distant metastases, particularly in the recurrent setting. FDG-PET is superior in detecting tumor-involved distant lymphnodes, particularly those which are normal in size, as well as in characterizing enlarged lymphnodes as positive or negative for malignancy. Of note, CT is superior in detecting small lung metastases. Although the overall sensitivity for bone scintigraphy and FDG-PET are comparable, bone scintigraphy seems to be superior in the detection of osteoblastic disease whereas FDG-PET is superior for osteolytic metastases, suggesting a complementary role for both imaging procedures. FDG-PET/MR has an evolving role in breast cancer management, for example in the detection of liver metastases and in the research setting for treatment monitoring. The utilization of PET for prediction of treatment response to primary chemotherapy is an area of active research, using FDG as well as other PET biomarkers including [F-18]Fluoroestradiol, [F-18]Fluorothymidine and integrin targeting tracer for monitoring anti-angiogenic therapy.

[Positron emission tomography/magnetic resonance: Present and future]. / Tomografía por emisión de positrones/resonancia magnética: presente y futuro.

PET/MRI has recently been introduced onto the market after several years of research and development. The simple notion of combining the molecular capabilities of the PET and its difference available radiotracers with the excellent tissue resolution of the MRI and wide range of multiparametric imaging techniques has generated great expectations upon the possible uses of this technology. Many challenges must be worked out. However, the most urgent one is the derivation of the MRI-based attenuation correction map. This is especially true because the PET/CT has already demonstrated a huge clinical impact within oncology, neurology and cardiology during its short existence. Despite these difficulties, research is being carried out at a rapid pace in the clinical setting in order to find areas in which the PET/MRI is superior to other existing imaging modalities. In the few initial publications found up to date that have analyzed its clinical role, areas have been identified where PET/CT can migrate to PET/MRI, even if only to suppress the CT scan's ionizing radiation. Nonetheless, there are many theoretical applications in which the PET/MRI can further improve the field of diagnostic imaging. In this article, we will review those applications, the evidence existing regarding the MRI and PET that support those premises as well as that which we have learned in the short period of one year with our experience using the PET/MRI.

Actualización en carcinoma diferenciado de tiroides refractario a radioyodo / Update on iodine-refractory differentiated thyroid carcinoma

La terapia con radioyodo constituye un pilar fundamental en la terapia adyuvante de rutina de los pacientes con carcinoma diferenciado de tiroides de alto riesgo. Sin embargo, un porcentaje no despreciable de estos pacientes desarrollaran un estado de refractariedad a este tratamiento, mostrando un peor pronóstico, disminuyendo la supervivencia y la esperanza de vida, lo que demuestra una clara necesidad de explorar distintos abordajes terapéuticos. El tratamiento de los pacientes refractarios al radioyodo sigue siendo un desafío, disponiendo en la actualidad de distintas opciones terapéuticas novedosas que deben ser conocidas por las distintas especialidades relacionadas con el carcinoma diferenciado de tiroides (CDT). El objetivo del presente trabajo es hacer una revisión del CDT refractario al tratamiento con yodo radiactivo, centrándose especialmente en la definición de yodorrefractariedad, destacando su importancia por su elevada mortalidad, e introducir las diferentes opciones terapéuticas disponibles para estos pacientes (AU)

Radioiodine therapy represents a fundamental pillar in the routine adjuvant therapy of patients with high-risk differentiated thyroid carcinoma. However, a non-negligible percentage of these patients will develop iodine refractoriness, showing a worse prognosis, as well a lower survival, which demonstrates a clear need to explore different therapeutic approaches. Iodine refractory patient treatment continues to be a challenge, currently having different novel therapeutic options that should be known by the different specialties related to differentiated thyroid carcinoma (DTC). The aim of this work is to review iodine refractory thyroid carcinoma treatment, focusing especially on the definition of iodine refractoriness, highlighting its importance due to its high mortality, and introducing the different therapeutic options available for these patients (AU)

[Abdominal splenosis: an often underdiagnosed entity]. / Esplenosis abdominal: una entidad frecuentemente infradiagnosticada.

Splenosis is defined as the heterotopic autotransplantation of splenic tissue because of a ruptured spleen due to trauma or surgery. It is a benign and incidental finding, although imaging tests may sometimes orient toward malignancy simulating renal tumors, abdominal lymphomas, endometriosis, among other. We report the case of a 42-year old male in whom a MRI was performed after a study due to abdominal pain. Multiple enlarged lymph nodes were observed in the abdomen, suggestive of lymphoproliferative disease. As an important background, splenectomy was carried out due to abdominal trauma at age 9. After several studies, it was decided to perform a (99m)Tc-labeled heat-damaged red blood cell scintigraphy that showed multiple pathological deposits distributed throughout the abdomen, and even the pelvis, being consistent with splenosis.

[Effective doses associated to the usual multimodal examinations in nuclear medicine]. / Dosis efectivas asociadas a las exploraciones multimodales habituales en medicina nuclear.

OBJECTIVE: To know the effective doses (E) that can be given in the common multimodal procedures in nuclear medicine, Single Photon Emission Tomography and Positron Emission Tomography, combined with Computed Tomography, SPECT/CT and PET/CT. Effective dose will be expressed according to Background Equivalent Radiation Time (BERT) and the contribution of the CT scan to the total dose will also be studied. MATERIAL AND METHODS: The effective dose of each procedure has been calculated as the sum of the external radiation dose (CT part) and internal one (radiopharmaceutical administration). Data from each side were collected through extensive literature search. RESULTS: A range of minimum and maximum effective dose [E(min), E(max)] associated with each procedure is shown. These doses range from 0.5 to 49.1 mSv. BERT ranges from 2.6 months to 20.4 years. The CT contribution to the total effective dose varies from 2.1% to 93%, according to the image acquisition protocol and its purpose. Performing a diagnostic CT scan increases the dose up to a factor of 4.3 times compared to the dose used for CT acquisition for attenuation correction and anatomic localization. CONCLUSIONS: This article focus on the effective dose level that can be given in multimodal procedures, bearing in mind that the data are subject to constant changes and should be updated periodically. It is important to know the dosimetric impact when the CT scan is added. The application of optimized protocols according to the indication of the study reduces the patient's exposure without the loss of significant information.