Pitfalls and Artifacts in the Use of PET/CT in Oncology Imaging

Overview of F18-FDG uptake patterns in retroperitoneal pathologies: imaging findings, pitfalls, and artifacts

INTRODUCTION

Retroperitoneum can be the origin of a wide variety of pathologic conditions and potential space for disease spread to other compartments of the abdomen and pelvis. Computed tomography (CT) and magnetic resonance imaging (MRI) are often the initial imaging modalities to evaluate the retroperitoneal pathologies, however given the intrinsic limitations, F18-FDG PET/CT provides additional valuable metabolic information which can change the patient management and clinical outcomes. We highlight the features of retroperitoneal pathologies on F18-FDG PET/CT and the commonly encountered imaging artifacts and pitfalls. The aim of this review is to characterize primary and secondary retroperitoneal pathologies based on their metabolic features, and correlate PET findings with anatomic imaging.

CONCLUSION

Retroperitoneal pathologies can be complex, ranging from oncologic to a spectrum of non-oncologic disorders. While crosse-sectional imaging (CT and MRI) are often the initial imaging modalities to localize and characterize pathologies, metabolic information provided by F18-FDG PET/CT can change the management and clinical outcome in many cases.

Application of an artificial intelligence-based tool in [18F]FDG PET/CT for the assessment of bone marrow involvement in multiple myeloma

PURPOSE

[18F]FDG PET/CT is an imaging modality of high performance in multiple myeloma (MM). Nevertheless, the inter-observer reproducibility in PET/CT scan interpretation may be hampered by the different patterns of bone marrow (BM) infiltration in the disease. Although many approaches have been recently developed to address the issue of standardization, none can yet be considered a standard method in the interpretation of PET/CT. We herein aim to validate a novel three-dimensional deep learning-based tool on PET/CT images for automated assessment of the intensity of BM metabolism in MM patients.

MATERIALS AND METHODS

Whole-body [18F]FDG PET/CT scans of 35 consecutive, previously untreated MM patients were studied. All patients were investigated in the context of an open-label, multicenter, randomized, active-controlled, phase 3 trial (GMMG-HD7). Qualitative (visual) analysis classified the PET/CT scans into three groups based on the presence and number of focal [18F]FDG-avid lesions as well as the degree of diffuse [18F]FDG uptake in the BM. The proposed automated method for BM metabolism assessment is based on an initial CT-based segmentation of the skeleton, its transfer to the SUV PET images, the subsequent application of different SUV thresholds, and refinement of the resulting regions using postprocessing. In the present analysis, six different SUV thresholds (Approaches 1-6) were applied for the definition of pathological tracer uptake in the skeleton [Approach 1: liver SUVmedian × 1.1 (axial skeleton), gluteal muscles SUVmedian × 4 (extremities). Approach 2: liver SUVmedian × 1.5 (axial skeleton), gluteal muscles SUVmedian × 4 (extremities). Approach 3: liver SUVmedian × 2 (axial skeleton), gluteal muscles SUVmedian × 4 (extremities). Approach 4: ≥ 2.5. Approach 5: ≥ 2.5 (axial skeleton), ≥ 2.0 (extremities). Approach 6: SUVmax liver]. Using the resulting masks, subsequent calculations of the whole-body metabolic tumor volume (MTV) and total lesion glycolysis (TLG) in each patient were performed. A correlation analysis was performed between the automated PET values and the results of the visual PET/CT analysis as well as the histopathological, cytogenetical, and clinical data of the patients.

RESULTS

BM segmentation and calculation of MTV and TLG after the application of the deep learning tool were feasible in all patients. A significant positive correlation (p < 0.05) was observed between the results of the visual analysis of the PET/CT scans for the three patient groups and the MTV and TLG values after the employment of all six [18F]FDG uptake thresholds. In addition, there were significant differences between the three patient groups with regard to their MTV and TLG values for all applied thresholds of pathological tracer uptake. Furthermore, we could demonstrate a significant, moderate, positive correlation of BM plasma cell infiltration and plasma levels of β2-microglobulin with the automated quantitative PET/CT parameters MTV and TLG after utilization of Approaches 1, 2, 4, and 5.

CONCLUSIONS

The automated, volumetric, whole-body PET/CT assessment of the BM metabolic activity in MM is feasible with the herein applied method and correlates with clinically relevant parameters in the disease. This methodology offers a potentially reliable tool in the direction of optimization and standardization of PET/CT interpretation in MM. Based on the present promising findings, the deep learning-based approach will be further evaluated in future prospective studies with larger patient cohorts.

Joint motion estimation and penalized image reconstruction algorithm with anatomical priors for gated TOF-PET/CT

The presence of respiratory motion not only degrades the reconstructed image but also limits the utilization of anatomical priors in emission tomography. In this study, we explore the potential application of a joint motion estimation and penalized image reconstruction algorithm using anatomical priors in gated time-of-flight positron emission tomography/computed tomography (PET/CT). The algorithm is able to warp both the activity image and the attenuation map to align them with the measured data with the facilitation of anatomical information contained in the attenuation map. Five patient datasets, three acquired in single-bed position and two acquired in whole-body continuous-bed-motion mode, are included. For each patient, the attenuation map is derived from a breath-hold CT. The Parallel Levels Sets (PLS) is chosen as a representative anatomical prior. In addition to demonstrating the reliability of the estimated motion and the benefits of incorporating anatomical prior, preliminary results also indicate that the algorithm shows the potential to reconstruct an activity image in the space corresponding to that of the attenuation map, which could be applied to address the potential misalignment issue in applications involving multiple PET acquisitions but a single CT.

Radiation Safety and Accidental Radiation Exposures in Nuclear Medicine

Medical radiation accidents and unintended events may lead to accidental or unintended medical exposure of patients and exposure of staff or the public. Most unintended exposures in nuclear medicine will lead to a small increase in risk; nevertheless, these require investigation and a clinical and dosimetric assessment. Nuclear medicine staff are exposed to radiation emitted directly by radiopharmaceuticals and by patients after administration of radiopharmaceuticals. This is particularly relevant in PET, due to the penetrating 511 keV γ-rays. Dose constraints should be set for planning the exposure of individuals. Staff body doses of 1-25 µSv/GBq are reported for PET imaging, the largest component being from the injection. The preparation and administration of radiopharmaceuticals can lead to high doses to the hands, challenging dose limits for radionuclides such as ⁹⁰Y and even ¹⁸F. The risks of contamination can be minimized by basic precautions, such as carrying out manipulations in purpose-built facilities, wearing protective clothing, especially gloves, and removing contaminated gloves or any skin contamination as quickly as possible. Airborne contamination is a potential problem when handling radioisotopes of iodine or administering radioaerosols. Manipulating radiopharmaceuticals in laminar air flow cabinets, and appropriate premises ventilation are necessary to improve safety levels. Ensuring patient safety and minimizing the risk of incidents require efficient overall quality management. Critical aspects include: the booking process, particularly if qualified medical supervision is not present; administration of radiopharmaceuticals to patients, with the risk of misadministration or extravasation; management of patients' data and images by information technology systems, considering the possibility of misalignment between patient personal data and clinical information. Prevention of possible mistakes in patient identification or in the management of patients with similar names requires particular attention. Appropriate management of pregnant or breast-feeding patients is another important aspect of radiation safety. In radiopharmacy activities, strict quality assurance should be implemented at all operational levels, in addition to adherence to national and international regulations and guidelines. This includes not only administrative aspects, like checking the request/prescription, patient's data and the details of the requested procedure, but also quantitative tests according to national/international pharmacopoeias, and measuring the dispensed activity with a calibrated activity meter prior to administration. In therapy with radionuclides, skin tissue reactions can occur following extravasation, which can result in localized doses of tens of Grays. Other relevant incidents include confusion of products for patients administered at the same time or malfunction of administration devices. Furthermore, errors in internal radiation dosimetry calculations for treatment planning may lead to under or over-treatment. According to literature, proper instructions are fundamental to keep effective dose to caregivers and family members after patient discharge below the Dose constraints. The IAEA Basic Safety Standards require measures to minimize the likelihood of any unintended or accidental medical exposures and reporting any radiation incident. The relative complexity of nuclear medicine practice presents many possibilities for errors. It is therefore important that all activities are performed according to well established procedures, and that all actions are supported by regular quality assurance/QC procedures.

FAPI-04 Uptake in Healthy Tissues of Cancer Patients in 68Ga-FAPI-04 PET/CT Imaging

Objective

The aim of this study is to investigate the uptake of ⁶⁸Ga-FAPI-04 in normal tissues and calculate standardized uptake values (SUVs) for various organs in the body.

Methods

A total of 49 patients who underwent ⁶⁸Ga-FAPI-04 PET/CT were included in our study. The following organs were identified on CT images: brain, parotid, and submandibular glands, palatine tonsils, thyroid, lymph nodes (if present), breasts, lungs, thymus, left ventricle walls, mediastinal blood pool, vertebral bone marrow, liver, spleen, pancreas, stomach, small and large intestines, adrenal glands, kidneys, uterus, testes, and prostate. Median, minimum, and maximum values (max) and average (avg) values of standard uptake value (SUV) of tissues and organs were calculated.

Results

The accumulation of ⁶⁸Ga-FAPI in normal organs showed variations. The cerebral/cerebellar cortex exhibited no ⁶⁸Ga-FAPI uptake, while the scalp showed low uptake. Low uptake was also observed in the lung parenchyma, esophagus, left ventricle walls, nipple, and glandular breast tissue. In the abdominopelvic area, the pancreas exhibited low uptake, which was higher in the tail region. Low uptake was observed in the renal cortex. Intense ⁶⁸Ga-FAPI uptake was observed throughout the uterus, which was higher in the corpus. There was no uptake of ⁶⁸Ga-FAPI in the bone cortex and medulla.

Conclusion

We determined the physiological uptake and SUVmax of FAPI-04 in different tissues and organs and created a guide for researchers.

Chest PET/MRI in Solid Cancers: Comparing the Diagnostic Performance of a Free-Breathing 3D-T1-GRE Stack-of-Stars Volume Interpolated Breath-Hold Examination (StarVIBE) Acquisition With That of a 3D-T1-GRE Volume Interpolated Breath-Hold Examination (VIBE) for Chest Staging During Whole-Body PET/MRI

BACKGROUND

Whole-body positron emission tomography/magnetic resonance imaging (WB-PET/MRI) is increasingly used in oncology. However, chest staging remains challenging.

PURPOSE

To compare the diagnostic performance of a free-breathing 3D-T1-GRE stack-of-stars volume interpolated breath-hold examination (StarVIBE) with that of a 3D-T1-GRE volume interpolated breath-hold examination (VIBE) during WB-PET/MRI for chest staging.

STUDY TYPE

Retrospective, cohort study.

POPULATION

One hundred and twenty-three patients were referred for initial staging of solid cancer, 46 of whom had pulmonary nodules and 14 had pulmonary metastasis.

FIELD STRENGTH/SEQUENCE

Free-breathing 3D-T1-GRE stack-of-stars (StarVIBE) and Cartesian 3D-T1-GRE VIBE at 3.0 T.

ASSESSMENT

Image quality was assessed using a 4-point scale and using the signal-to-noise ratio (SNR) of lung parenchyma and contrast-to-noise ratio (CNR) of pulmonary nodules. Diagnostic performances of both sequences were determined by three independent radiologists for detection of pulmonary nodules, lymph node involvement, and bone metastases using chest CT, pathology, and follow-up as reference standards.

STATISTICAL TESTS

Paired Student's t-test; chi-squared; Fisher's exact test. A P value <0.05 was considered statistically significant.

RESULTS

StarVIBE quality was judged as better in 34% of cases and at least equivalent to VIBE in 89% of cases, with significantly higher quality scores (4 [4-4] vs. 3 [3-4], respectively). SNR and CNR values were significantly higher with StarVIBE (8 ± 1.3 and 9.7 ± 4.6, respectively) than with VIBE (1.8 ± 0.2 and 5.5 ± 3.3, respectively). Compared to VIBE, StarVIBE showed significantly higher sensitivity (73% [95% CI 62-82] vs. 44% [95% CI 33-55], respectively) and specificity (95% [95% CI 88-99] vs. 67% [95% CI 56-77]) for pulmonary nodules detection and significantly higher sensitivity (100% [95% CI 89-100] vs. 67% [95% CI 48-82], respectively) for detection of lymph node involvement. Sensitivities for bone metastases detection were not significantly different (100% [95% CI 88-100] vs. 82% [95% CI 63-94], P = 0.054).

DATA CONCLUSION

Owing to improved SNR and CNR and spatial resolution, a free-breathing 3D stack-of-stars T1-GRE sequence improves chest staging in comparison with standard 3D-T1-GRE VIBE and may be integrated in WB-PET/MRI acquisitions for initial staging of solid cancer.

LEVEL OF EVIDENCE

3 TECHNICAL EFFICACY: Stage 2.

Increased FDG Uptake of the Pectoral Girdle and Serratus Anterior Due to Wallpaper Stripping on PET/CT-Exquisite Demonstration of the Biomechanics

ABSTRACT

According to published guidelines and routine procedures, patients are instructed to avoid strenuous exercise for 6 to 24 hours before FDG imaging, avoiding unfavorable muscular uptake. A 40-year-old man with esophageal carcinoma underwent FDG PET/CT for response assessment. Intense uptake was noted in the muscles of the right upper limb and chest. The patient stated he had avoided exercise before scanning. On further questioning, he was found to be a professional painter and decorator and had been working stripping wallpaper. Marked skeletal FDG uptake occurs in subjects who have strenuously exerted themselves before or after the injection of FDG.

Pitfalls on PET/CT Due to Artifacts and Instrumentation

PET/CT has become a preferred imaging modality over PET-only scanners in clinical practice. However, along with the significant improvement in diagnostic accuracy and patient throughput, pitfalls on PET/CT are reported as well. This review provides a general overview on the potential influence of the limitations with respect to PET/CT instrumentation and artifacts associated with the modality integration on the image appearance and quantitative accuracy of PET. Approaches proposed in literature to address the limitations or minimize the artifacts are discussed as well as their current challenges for clinical applications. Although the CT component can play an important role in assisting clinical diagnosis, we concentrate on the imaging scenarios where CT is used to provide auxiliary information for attenuation compensation and scatter correction in PET.

Infection Control of COVID-19: Surgical Mask-Related Facial Cutaneous Artifact on FDG PET/CT

ABSTRACT

In accordance with published international COVID-19 pandemic guidance (American College of Nuclear Medicine, British Nuclear Medicine Society, and European Association of Nuclear Medicine), the use of face masks has become an essential part of infection control for both patients and staff. A 56-year-old man with mantle cell lymphoma underwent staging FDG PET/CT, which demonstrated avid lymphadenopathy below the diaphragm and an unusual diffuse FDG uptake projected over the face, raising the suspicion of cutaneous lymphomatous involvement. On reflection of the clinical scenario and scanning conditions, cutaneous involvement was discounted; the pattern of uptake and lack of CT correlate were supportive of a cutaneous artifact related to the presence of the patient's mask.

The hot embolus of 18F-fluorodeoxyglucose

Scanning oncological patients with ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) for their disease staging, evaluation of treatment response, and monitoring/management has become a standard of care. The use of the radioactive fluorine in the FDG molecule helps establish cell/tissue lines high on glucose consumption and hence metabolically active. Abnormalities are detected on the scan as areas of increased uptake. However, these areas of increased (hot) uptakes do not necessarily translate into a pathological finding. A comprehensive knowledge of the uptakes of the tracer and the potential "pitfalls" that may be associated with them should be known and kept in mind during scan reading. One such pitfall is the "hot clot" or "pulmonary emboli," and we report two such cases encountered at our setup and discuss their causes and how they should be identified and avoided.

Potential role of 18F-FDG PET/CT in a case of progressive Rosai Dorfman disease

Rosai Dorfman disease is a rare form of nonlangerhans cell histiocytosis, presenting with extensive lymphadenopathies. Treatment in most cases of nodal disease, involves close observation; however, extranodal involvement requires a more definitive treatment strategy. Herein, we report a case of extensive Rosai Dorfman disease in a 43-year-old woman presenting for evaluation of treatment response by 18F-FDG PET/CT after frequent relapses and disease progression. In addition to extensive lymphadenothapies in cervical, supraclavicular, superior mediastinum, axillary, abdominopelvic and inguinofemoral regions, the patient had metabolically active bone and subcutaneous lesions which were not previously recognized. Following this 18F-FDG PET/CT study, the patient management was changed to sirolimus and prednisolone. To choose the best treatment option for Rosai Dorfman patients, knowledge of the full extent of disease is important. Compared with conventional imaging, 18F-FDG PET/CT has the advantage of being a whole-body imaging modality and can recognize disease involvement prior to any anatomical changes.

Additional Value of 2-[18F]FDG PET/CT Comparing to MRI in Treatment Approach of Anal Cancer Patients

Accurate staging and treatment planning are imperative for precise management in Anal Cancer (ACa) patients. We aimed to evaluate the additive and prognostic value of pre-treatment 2-[¹⁸F]fluoro-2-deoxy-d-glucose positron emission tomography/computed tomography (2-[¹⁸F]FDG PET/CT) in the staging and management of ACa compared to magnetic resonance imaging (MRI). This retrospective study was conducted on 54 patients. Pre-treatment 2-[¹⁸F]FDG PET/CT studies and MRI reports were compared considering the primary tumor, pelvic lymph nodes, and metastatic lesions. The impact of 2-[¹⁸F]FDG PET/CT in the management and its prognostic value, using maximum standardized uptake value (SUVmax), were assessed. Discordant findings were found in 46.3% of patients (5 in T; 1 in T and N; 18 in N; and 1 in M stage). 2-[¹⁸F]FDG PET/CT resulted in up-staging in 9.26% and down-staging in 3.7% of patients. Perirectal lymph nodes were metabolically inactive in 12.9% of patients. Moreover, 2-[¹⁸F]FDG PET/CT resulted in management change in 24.1% of patients. Finally, SUVmax provided no prognostic value. 2-[¹⁸F]FDG PET/CT altered staging and management in a sizable number of patients in this study, and supports a need for a change in guidelines for it to be used as a routine complementary test in the initial management of ACa.

68Ga/64Cu PSMA Bio-Distribution in Prostate Cancer Patients: Potential Pitfalls for Different Tracers

BACKGROUND

68Ga-PSMA is a widely useful PET/CT tracer for prostate cancer imaging. Being a transmembrane protein acting as a glutamate carboxypeptidase enzyme, PSMA is highly expressed in prostate cancer cells. PSMA can also be labeled with 64Cu, offering a longer half-life and different resolution imaging. Several studies documented bio-distribution and pitfalls of 68Ga-PSMA as well as of 64Cu- PSMA. No data are reported on differences between these two variants of PSMA. Our aim was to evaluate physiological distribution of these two tracers and to analyze false positive cases.

METHODS

We examined tracer bio-distribution in prostate cancer patients with negative 68Ga-PSMA PET/CT (n=20) and negative 64Ga-PSMA PET/CT (n=10). A diagnostic pitfall for each tracer was documented.

RESULT

Bio-distribution of both tracers was similar, with some differences due to renal excretion of 68Ga- PSMA and biliary excretion of 64Cu-PSMA. 68Ga-PSMA uptake was observed in sarcoidosis while 64Cu- PSMA uptake was recorded in pneumonitis.

DISCUSSION

Both tracers may present similar bio-distribution in the human body, with similar uptake in exocrine glands and high intestinal uptake. Similarly to other tracers, false positive cases cannot be excluded in clinical practice.

CONCLUSION

The knowledge of difference in bio-distribution between two tracers may help in interpretation of PET data. Diagnostic pitfalls can be documented, due to the possibility of PSMA uptake in inflammation. Our results are preliminary to future studies comparing diagnostic accuracies of 68Ga-PSMA and 64Cu-PSMA.

Molecular Imaging for Particle Therapy: Current Approach and Future Directions

During the last decades, radiation oncology has been subject to a number of technological innovations. Particle therapy has evolved in parallel to the modern high-precision photon radiotherapy techniques and offers a superior dose distribution with decreased integral dose to healthy tissues. With advancing precision of treatment, the necessity for accurate and confident target volume delineation is rising. When morphological imaging reaches its limitations, molecular imaging can provide valuable information.

11C-Choline PET/CT in Recurrent Prostate Cancer: Retrospective Analysis in a Large U.S. Patient Series

Our purpose was to evaluate the performance of ¹¹C-choline PET/CT in detecting biochemically recurrent prostate cancer (PCa) in a large non-European cohort (in the context of emerging evidence for prostate-specific membrane antigen PET in this setting) and to map patterns of PCa recurrence. Methods: We retrospectively analyzed ¹¹C-choline PET/CT scans from 287 patients who were enrolled in an imaging protocol based on rising prostate-specific antigen (PSA) levels (mean, 3.43 ng/mL; median, 0.94 ng/mL; range, 0.15-89.91 ng/mL) and suspected recurrent PCa. A total of 187 patients had undergone primary radical prostatectomy (RP) (79/187 had secondary radiotherapy), 30 had undergone primary radiotherapy, and 70 had a persistent PSA elevation after receiving initial treatment (69 after RP, 1 after radiotherapy). The level of suspicion for recurrence on ¹¹C-choline PET/CT was scored (0, negative; 1, equivocal; 2, positive) by 2 readers. The correlation between ¹¹C-choline PET/CT positivity and initial treatment, Gleason score, National Comprehensive Cancer Network stage, PSA level, PSA doubling time, PSA velocity, and time between initial treatment and PET imaging was evaluated. Prostate Cancer Molecular Imaging Standardized Evaluation (PROMISE) criteria were used to map ¹¹C-choline recurrence patterns. Results: Considering scores 1 and 2 as positives, consensus between the 2 readers deemed 66% of the ¹¹C-choline PET/CT scans as positive. When sorted by PSA level, 45% of patients with a PSA of less than 0.5 ng/mL, 56% of patients with a PSA of 0.5-0.99 ng/mL, 70% of patients with a PSA of 1.0-1.99 ng/mL, and 90% of patients with a PSA of at least 2.0 ng/mL scored either 1 or 2 on ¹¹C-choline PET/CT scans. When considering scores of 2 only, ¹¹C-choline PET/CT positivity was 54% (28%, 46%, 62%, and 81%, respectively, for patients with PSA < 0.5 ng/mL, 0.5-0.99 ng/mL, 1.0-1.99 ng/mL, and ≥ 2.0 ng/mL). In multivariate analysis, only PSA level was significantly associated with scan positivity. Pattern analysis showed that pelvic lymph nodes were the most common site of recurrence, and 28% of patients had ¹¹C-choline-positive suspected recurrences outside the initial treatment field. Conclusion: ¹¹C-choline PET/CT can detect PCa recurrence even among patients with low PSA levels when interpretation accounts for the clinical context, providing a certain pretest probability. Until prostate-specific membrane antigen agents are fully approved for PCa, choline PET/CT may provide clinical utility.

Patient Repositioning Reveals a Malignant Pleura Effusion Initially Mistaken as a Bone Metastasis on 18FDG PET/CT

A 70-year-old woman with breast cancer underwent F-FDG PET/CT for restaging. An FDG-avid focus corresponding to a rib on CT images was identified and interpreted as suggestive of an osseous metastasis. A PET/CT-guided biopsy was planned with the patient in prone position. Prone images demonstrated the FDG focus "moved" to the anterior chest and corresponding to pleural fluid. The diagnosis was altered from osseous metastases to pleural malignancy, and the bone biopsy was not performed. This case not only emphasizes the sensitivity of PET in the detection of malignancy, but also highlights the difficulty localizing small, mobile, FDG-avid foci.

Prognostic value of volumetric metabolic parameter changes determined by during and after radiotherapy-based 18 F-FDG PET/CT in stage III non-small cell lung cancer

The aim of this prospective study was to evaluate the prognostic value of volumetric metabolic parameters assessed by during and after radiation-based therapy ¹⁸ F-FDG PET/CT in patients with stage III non-small cell lung cancer (NSCLC). We enrolled stage III NSCLC patients who had planned to receive definitive chemo-radiation or radiotherapy (RT) and underwent ¹⁸ F-FDG PET/CT before treatment (PET1), during RT (at the fifth week, PET2) and after treatment (3 months later, PET3). By comparing with PET1, percentage changes of metabolic tumor volume (ΔMTV) and tumor total lesion glycolysis (ΔTLG) of PET2 and PET3 were calculated. We used medians of ΔTLG and ΔMTV as cut-off values to stratify patients. Their prognostic values were evaluated by progression-free survival (PFS) and overall survival (OS). Thirty patients were enrolled initially. Five were excluded due to multiple metastases or double cancer. The remaining 25 patients had PET2 at a median of 46 Gy. Data on PET3 were available in 19 patients. During-RT ΔTLG (cut-off: 65%) was a significant prognostic factor for PFS (P = 0.02) and OS (P < 0.01). During-RT ΔMTV (cut-off: 42%) had marginal significance for PFS (P = 0.07) and was significant for OS (P = 0.02). Of the PET3 parameters, neither ΔTLG nor ΔMTV was a significant prognostic factor for PFS and OS. We conclude that ΔTLG of during-RT ¹⁸ F-FDG PET/CT may predict treatment response and thus provide opportunities to modify treatment for poor responders.

Normal bone and soft tissue distribution of fluorine-18-sodium fluoride and artifacts on 18F-NaF PET/CT bone scan: a pictorial review

Fluorine-18-sodium fluoride (F-NaF) PET/CT is a relatively new and high-resolution bone imaging modality. Since the use of F-NaF PET/CT has been increasing, it is important to accurately assess the images and be aware of normal distribution and major artifacts. In this pictorial review article, we will describe the normal uptake patterns of F-NaF in the bone tissues, particularly in complex structures, as well as its physiologic soft tissue distribution and certain artifacts seen on F-NaF PET/CT images.

Granulomatous Lymphangitis Masquerading as Relapsed Hodgkin Disease on FDG PET/CT

A 38-year-old woman with Hodgkin lymphoma was referred for staging fludeoxyglucose (18F) positron emission tomography/computed tomography (FDG PET/CT) that showed widespread intensely FDG-avid disease in multiple nodal stations above the diaphragm and spleen and extranodal involvement in the lungs and vertebral bodies. She underwent chemotherapy and radiotherapy. Progress FDG PET/CT 5 months later showed significant metabolic and anatomic response. Repeat FDG PET/CT 1 month later was highly suspicious of recurrent disseminated FDG-avid lymphoma in multiple nodal stations above and below the diaphragm, spleen, multiple bones, and lungs. Subsequent bone marrow biopsy showed sarcoid-like granulomatous inflammation with no evidence of lymphoma. The patient was clinically well and no active treatment was instituted. Subsequent FDG PET/CT 2 months later showed complete resolution of metabolic activity.

Granuloma Mimicking Local Recurrence on PET/CT after Liver Resection of Colorectal Liver Metastasis: A Case Report

Positron emission tomography–computed tomography (PET/CT) improves the diagnostic interpretation of fluorine-18 fluorodeoxyglucose (18F-FDG ) PET and CT in oncologic patients and has an impact on both diagnostic and therapeutic aspects of patient management. However, false positive findings from the PET/CT imaging should be taken into consideration as they mislead physicians into improper therapeutic actions. We present a 48-year-old female patient with a history of left colectomy for colorectal cancer and subsequent liver metastasectomy. After one year of follow-up, she presented with a highly suspicious lesion in the liver, which was confirmed on PET/CT as a metastatic liver tumor. Consequently, the patient underwent surgical excision of the tumor, and the definitive histological diagnosis showed a granulomatous tissue with giant cells and foreign body tissue reaction. Based on this report, we briefly review the dangerous pitfalls from radiological and PET/CT imaging concerning the preoperative diagnostic workup examination, as they may significantly alter the treatment plan in oncologic patients.