The combination of positron emission tomography (PET) with magnetic resonance imaging (MRI) has been the subject of several studies in recent years. Positron emission tomography is the most sensitive and specific imaging modality in the detection of metabolic changes, but presents limited spatial resolution. On the other hand, MRI presents a significant spatial resolution, besides evaluating soft tissues signal intensity with excellent contrast resolution. The present iconographic essay is aimed at demonstrating the potential clinical application of PET/MRI coregistration. The studies were performed in a dedicated PET unit with 18F-fluorodeoxyglucose (FDG) as radiopharmaceutical and coregistered with 1.5 T or 3 T brain MRI. The brain images fusion software presents an already well-established accuracy, so a significant synergy between a functional PET study and an excellent MRI anatomical detail is achieved. The most attractive clinical applications of this approach are the following: epileptogenic zone assessment in patients refractory to drug therapy, identification of patients with cognitive impairment at higher risk for progression to dementia and differentiation of dementias and Parkinsonian syndromes.

Keywords: Fluorodeoxyglucose, FDG, Positron emission tomography, PET, Magnetic resonance imaging, Fusion, Clinical neurology

OBJECTIVE: The present study is aimed at validating a 3D acquisition protocol for positron emission tomography as a replacement for the 2D mode, to reduce the radiation dose delivered to patients, without any loss in the quality of images. MATERIALS AND METHODS: The study comprised 27 simulations in a Discovery ST equipment with four-minute 2D acquisitions, and two-minute and four-minute 3D acquisitions, utilizing a chest phantom according to the National Electrical Manufacturers Association protocol. Six spheres with different diameters were inserted into this phantom as a means for determining the images quality. The images were blindly reviewed by three experienced nuclear physicians who did not know the acquisition modes. Each observer attributed a score 1 when one of the spheres was not identified, or 2 for visible spheres. RESULTS: The qualitative analysis based on generalized kappa coefficient demonstrated that the frequency of visible spheres was higher with four-minute 3D acquisitions (85%), with an also higher interobserver agreement (88.9%), generalized kappa = 0.725 [0.507;0.942]. CONCLUSION: The protocol with four-minute 3D acquisition with lower 18F-FDG activity can be utilized for patients with a biotype similar to the phantom, without any loss in the imaging quality.

Keywords: PET/CT, Imaging quality, 2D mode, 3D mode, 18F-FDG, Dose reduction

Malignant melanoma is a common and aggressive disease that frequently causes metastases to the small bowel. This study illustrates a case of small bowel intussusception secondary to metastatic melanoma visualized at 18F-FDG PET/CT in a 48-year-old woman who had this examination for restaging purposes.

Keywords: PET/CT, Melanoma, Intussusception

Radiation therapy represents an important alternative for curative treatment of patients with nonsmall cell lung cancer. However, an accurate definition of the volume to be irradiated becomes even more important, considering that lungs are highly sensitive to radiation. Most recently, combined FDG-PET/CT scan has been utilized, and the literature reports its significant role in the planning of radiation therapy, since it seems to influence the target-volume delineation in cases of lung cancer. Differences between diagnostic and treatment equipments must be taken into consideration when FDG-PET/CT scan is utilized in the planning of radiation therapy. The present study discusses some of the many technical problems that must be solved when PET is incorporated into the planning of radiation therapy for non-small cell lung cancer.

Keywords: Radiotherapy, PET scan, Planning, Lung cancer

The authors present a list of recommendations on the utilization of 18F-FDG PET/CT in oncology for the diagnosis, staging and detection of cancer, as well as in the follow-up of the disease progression and possible recurrence. The recommendations were based on the analysis of controlled studies and a systematic review of the literature including both retrospective and prospective studies regarding the clinical usefulness and the impact of 18F-FDG PET/CT on the management of cancer patients. 18F-FDG PET/CT should be utilized as a supplement to other conventional imaging methods such as computed tomography and magnetic resonance imaging. Positive results suggesting changes in the clinical management should be confirmed by histopathological studies. 18F-FDG PET should be utilized in the diagnosis and appropriate clinical management of cancer involving the respiratory system, head and neck, digestive system, breast, genital organs, thyroid, central nervous system, besides melanomas, lymphomas and occult primary tumors.

Keywords: FDG-PET; Oncology; Diagnosis; Clinical indications.

Breast hemangioma is a rare benign tumor that presents either absent or low 18F-fluoro-2-deoxy-D-glucose (FDG) uptake at positron emission tomography (PET). The authors report the case of a breast nodule pathologically compatible with hemangioma in a woman whose PET-scan has demonstrated increased FDG uptake (simulating a malignant tumor). A brief review of factors leading to false positive and false negative PET results is also undertaken.

Keywords: PET/CT; FDG-18F; Hemangioma; Breast.

OBJECTIVE: To evaluate the accuracy and cost-effectiveness of metabolic staging (MS) with FDG-PET as compared with the conventional staging (CS) strategy in the preoperative staging of non-small cell lung cancer (NSCLC). MATERIALS AND METHODS: A total of 95 patients with initial diagnosis of NSCLC were staged before undergoing treatment. The MS and CS results were compared with regard to treatment definition and incidence of futile thoracotomies with both strategies. RESULTS: Metabolic staging with FDG-PET upstaged 48.4% and downstaged 5.3% of the patients, and would lead to change in the treatment of 41% of cases. Thoracotomy was considered as futile in 47% of the patients with CS, and in 19% of the patients with MS. The cost of futile thoracotomies in eight patients with MS was R$ 79,720, while in 31 patients with CS it would be R$ 308,915. Just such saving in costs would be more than enough to cover the costs of all FDG-PETs (R$ 126,350) or FDG-PET/CTs (R$ 193,515) for the 95 patients. CONCLUSION: The metabolic staging with FDG-PET is more accurate than CS in patients with NSCLC. Both FDG-PET and FDG-PET/CT are cost-effective methods and their utilization is economically justifiable in the Brazilian public health system.

Keywords: Non-small cell lung cancer; FDG-PET; Staging; Cost-effectiveness.

OBJECTIVE: To correlate the results of ¹⁸F-fluoro-2-deoxy-D-glucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT) performed with a specific protocol for assessment of breasts with histological/immunohistochemical findings in breast carcinoma patients. MATERIALS AND METHODS: Cross-sectional study with prospective data collection, where patients with biopsy-confirmed breast carcinomas were studied. The patients underwent PET/CT examination in prone position, with a specific protocol for assessment of breasts. PET/CT findings were compared with histological and immunohistochemical data. RESULTS: The authors identified 59 malignant breast lesions in 50 patients. The maximum diameter of the lesions ranged from 6 to 80 mm (mean: 32.2 mm). Invasive ductal carcinoma was the most common histological type (n = 47; 79.7%). At PET/CT, 53 (89.8%) of the lesions demonstrated anomalous concentrations of ¹⁸F-FDG, with maximum SUV ranging from 0.8 to 23.1 (mean: 5.5). A statistically significant association was observed between higher values of maximum SUV and histological type, histological grade, molecular subtype, tumor diameter, mitotic index and Ki-67 expression. CONCLUSION: PET/CT performed with specific protocol for assessment of breasts has demonstrated good sensitivity and was associated with relevant histological/immunohistochemical factors related to aggressiveness and prognosis of breast carcinomas.

Keywords: Breast cancer; PET/CT; Histology.

OBJECTIVE: The present study was aimed at evaluating the effective radiation dose in patients submitted to PET/CT for the diagnosis of mild cognitive impairment. MATERIALS AND METHODS: TLD-100 detectors inserted into an Alderson Rando® anthropomorphic phantom were utilized to measure the absorbed dose coming from the CT imaging modality. The anthropomorphic phantoms (male and female adult versions) were submitted to the same technical protocols for patients' images acquisition. The absorbed dose resulting from the radiopharmaceutical injection was estimated by means of the model proposed by the ICRP publication 106. RESULTS: The effective dose in patients submitted to this diagnostic technique was approximately (5.34 ± 1.99) mSv. CONCLUSION: Optimized protocols for calculation of radioactive activity injected into patients submitted to this diagnostic technique might contribute to reduce the effective radiation dose resulting from PET/CT in the diagnosis of mild cognitive impairment.

Keywords: Dosimetry; PET/CT; Mild cognitive impairment.

OBJECTIVE: To evaluate the level of ambient radiation in a PET/CT center. MATERIALS AND METHODS: Previously selected and calibrated TLD-100H thermoluminescent dosimeters were utilized to measure room radiation levels. During 32 days, the detectors were placed in several strategically selected points inside the PET/CT center and in adjacent buildings. After the exposure period the dosimeters were collected and processed to determine the radiation level. RESULTS: In none of the points selected for measurements the values exceeded the radiation dose threshold for controlled area (5 mSv/year) or free area (0.5 mSv/year) as recommended by the Brazilian regulations. CONCLUSION: In the present study the authors demonstrated that the whole shielding system is appropriate and, consequently, the workers are exposed to doses below the threshold established by Brazilian standards, provided the radiation protection standards are followed.

Keywords: Dosimetry; Thermoluminescence dosimetry; PET/CT.

OBJECTIVE: To analyze standardized uptake values (SUVs) using three different tube current intensities for attenuation correction on ¹⁸FNaF PET/CT scans. MATERIALS AND METHODS: A total of 254 ¹⁸F-NaF PET/CT studies were analyzed using 10, 20 and 30 mAs. The SUVs were calculated in volumes of interest (VOIs) drawn on three skeletal regions, namely, right proximal humeral diaphysis (RH), right proximal femoral diaphysis (RF), and first lumbar vertebra (LV1) in a total of 712 VOIs. The analyses covered 675 regions classified as normal (236 RH, 232 RF, and 207 LV1). RESULTS: Mean SUV for each skeletal region was 3.8, 5.4 and 14.4 for RH, RF, and LV1, respectively. As the studies were grouped according to mAs value, the mean SUV values were 3.8, 3.9 and 3.7 for 10, 20 and 30 mAs, respectively, in the RH region; 5.4, 5.5 and 5.4 for 10, 20 and 30 mAs, respectively, in the RF region; 13.8, 14.9 and 14.5 for 10, 20 and 30 mAs, respectively, in the LV1 region. CONCLUSION: The three tube current values yielded similar results for SUV calculation.

Keywords: ¹⁸F-NaF PET/CT; SUV; Tube current; mAs.

OBJECTIVE: To evaluate the prevalence of exclusive lower extremity metastases, specifically in the femur and below the knee, observed at ¹⁸F-NaF PET/CT. MATERIALS AND METHODS: One thousand consecutive PET/CT studies were retrospectively evaluated for the presence of exclusive uptake in lower extremities suggesting metastatic involvement. The presumptive diagnoses based on such uptakes were subsequently obtained by evaluation of other imaging studies. RESULTS: No exclusive uptake suggestive of metastasis below the femur was observed in the present series. Exclusive uptake was observed in the proximal femur with a presumptive diagnosis of metastasis in two patients. CONCLUSION: The prevalence of exclusive metastasis below the femur is low and scanning from head to knees is appropriate in most cases.

Keywords: PET/CT; ¹⁸F-NaF; Scintigraphy; Bone; Metastasis.

OBJECTIVE: To assess the cutoff values established by ROC curves to classify ¹⁸F-NaF uptake as normal or malignant. MATERIALS AND METHODS: PET/CT images were acquired 1 hour after administration of 185 MBq of ¹⁸F-NaF. Volumes of interest (VOIs) were drawn on three regions of the skeleton as follows: proximal right humerus diaphysis (HD), proximal right femoral diaphysis (FD) and first vertebral body (VB1), in a total of 254 patients, totalling 762 VOIs. The uptake in the VOIs was classified as normal or malignant on the basis of the radiopharmaceutical distribution pattern and of the CT images. A total of 675 volumes were classified as normal and 52 were classified as malignant. Thirty-five VOIs classified as indeterminate or nonmalignant lesions were excluded from analysis. The standardized uptake value (SUV) measured on the VOIs were plotted on an ROC curve for each one of the three regions. The area under the ROC (AUC) as well as the best cutoff SUVs to classify the VOIs were calculated. The best cutoff values were established as the ones with higher result of the sum of sensitivity and specificity. RESULTS: The AUCs were 0.933, 0.889 and 0.975 for UD, FD and VB1, respectively. The best SUV cutoffs were 9.0 (sensitivity: 73%; specificity: 99%), 8.4 (sensitivity: 79%; specificity: 94%) and 21.0 (sensitivity: 93%; specificity: 95%) for UD, FD and VB1, respectively. CONCLUSION: The best cutoff value varies according to bone region of analysis and it is not possible to establish one value for the whole body.

Keywords: ¹⁸F-NaF PET/CT; ROC curve; Cutoff values; Normal uptake; Malignant uptake

PET/CT is widely used for the evaluation of patients with thoracic malignancies. Although the levels of ¹⁸F-fluorodeoxyglucose (FDG) uptake are usually high in neoplastic diseases, they can also be physiological, due to artifacts. In addition, FDG uptake can occur in benign conditions such as infectious, inflammatory, and iatrogenic lesions. Furthermore, some malignant tumors, such as adenocarcinoma in situ (formerly known as bronchoalveolar carcinoma) and carcinoid tumors, may not show FDG uptake. Here, we illustrate the main pitfalls and artifacts in the interpretation of the results of oncologic PET/CT of the chest, outlining strategies for avoiding misinterpretation.

Keywords: Pitfalls; Chest; PET/CT; Oncology.

Os nervos cranianos representam extensões das estruturas funcionais do cérebro que cruzam a cabeça e o pescoço. Eles estão ligados a diferentes estruturas cranianas e se relacionam com diversas doenças. Uma compreensão profunda de sua complexa anatomia e aparência normal de imagem permite ao examinador identificar e caracterizar com mais precisão as anormalidades. A ressonância magnética com contraste é uma importante ferramenta para avaliar essas estruturas, especialmente as sequências tridimensionais de precessão livre de estado estacionário, que proporcionam alta resolução espacial e de partes moles, apesar da fina espessura dos nervos cranianos. Na maioria dos casos, os achados de imagem são inespecíficos, e uma anamnese completa, exame físico dirigido e testes laboratoriais são necessários para estreitar o diagnóstico diferencial. Este ensaio iconográfico ilustra e discute doenças congênitas, traumáticas e vasculares dos nervos cranianos, mostrando imagens em uma abordagem fisiopatológica.

Keywords: Neuroimagem/métodos; Radiologia/métodos; Ressonância magnética/métodos; Nervos cranianos/diagnóstico por imagem.