Relapsing polychondritis on PET/CT

Relapsing polychondritis is a rare multisystemic disease, which is characterized by recurrent inflammation of the cartilaginous structures. We report a case of a 37-year-old man with progressive respiratory distress. Chest Computed tomography (CT) demonstrated increased attenuation and smooth thickening of airway walls. Positron emission tomography/CT scan identified the multisystemic cartilaginous abnormalities that were recognized by an increased fluorine-18 deoxyglucose uptake on nasal cartilages, laryngeal cartilages, tracheobronchial tree, and rib cartilages. Positron emission tomography/CT is a useful tool to diagnose relapsing polychondritis, as the condition shows multisystemic cartilaginous abnormalities that can be identified by an increased fluorine-18 deoxyglucose uptake.     

PET/CT of a brodie abscess

Brodie abscess is a rare, localized type of subacute or chronic pyogenic osteomyelitis, usually of staphylococcal origin. Imaging with standard radiographs, bone scintigraphy, and MRI has been described in the literature. We present the case of a 28-year-old patient with pain in the right knee. Whole-body FDG-PET/CT scan showed a solitary FDG-active (SUV max 5.2) intracortical lesion in the meta-/epiphysis of the proximal tibia. CT demonstrated a sclerotic rim around the lesion. A Brodie abscess was considered a possible diagnosis. Multifocality could be excluded. CT-guided transosseous biopsy and curettage was performed and the diagnosis of a Brodie abscess was confirmed.     

PET/CT artifacts

There are several artifacts encountered in positron emission tomography/computed tomographic (PET/CT) imaging, including attenuation correction (AC) artifacts associated with using CT for AC. Several artifacts can mimic a 2-deoxy-2-[18F] fluoro-d-glucose (FDG) avid malignant lesions and therefore recognition of these artifacts is clinically relevant. Our goal was to identify and characterize these artifacts and also discuss some protocol variables that may affect image quality in PET/CT.     

Metallic artifacts caused by dental metal prostheses on PET images: a PET/CT phantom study using different PET/CT scanners

Objective  The objective of this study was to investigate the effects of computed tomography (CT) artifacts caused by dental metal prostheses on positron emission tomography (PET) images. Methods  A dental arch cast was fixed in a cylindrical water-bath phantom. A spherical phantom positioned in the vicinity of the dental arch cast was used to simulate a tumor. To simulate the tumor imaging, the ratio of the ¹⁸F-fluoro-deoxy-glucose radioactivity concentration of the spherical phantom to that of the water-bath phantom was set at 2.5. A dental bridge composed of a gold–silver–palladium alloy on the right mandibular side was prepared. A spherical phantom was set in the white artifact area on the CT images (site A), in a slightly remote area from the white artifact (site B), and in a black artifact area (site C). A PET/CT scan was performed with and without the metal bridge at each simulated tumor site, and the artifactual influence was evaluated on the axial attenuation-corrected (AC) PET images, in which the simulated tumor produced the strongest accumulation. Measurements were performed using three types of PET/CT scanners (scanners 1 and 2 with CT-based attenuation correction, and 3 with Cesium-137 (¹³⁷Cs)-based attenuation correction). The influence of the metal bridge was evaluated using the change rate of the SUVmean with and without the metal bridge. Results  At site A, an overestimation was shown (scanner 1: +5.0% and scanner 2: +2.5%), while scanner 3 showed an underestimation of −31.8%. At site B, an overestimation was shown (scanner 1: +2.1% and scanner 2: +2.0%), while scanner 3 showed an underestimation of −2.6%. However, at site C, an underestimation was shown (scanner 1: −25.0%, scanner 2: −32.4%, and scanner 3: −8.4%). Conclusions  When CT is used for attenuation correction in patients with dental metal prostheses, an underestimation of radioactivity of accumulated tracer is anticipated in the dark streak artifact area on the CT images. In this study, the dark streak artifacts of the CT caused by metallic dental prostheses may cause false negative finding of PET/CT in detecting small and/or low uptake tumor in the oral cavity.     

PET/CT in lymphoma: prospective study of enhanced full-dose PET/CT versus unenhanced low-dose PET/CT.

PET/CT combines functional and morphologic data and increases diagnostic accuracy in a variety of malignancies. This study prospectively compares the agreement between contrast-enhanced full-dose PET/CT and unenhanced low-dose PET/CT in lesion detection and initial staging of Hodgkin's disease and non-Hodgkin's lymphoma. METHODS: Forty-seven biopsy-proven lymphoma patients underwent a 18F-FDG PET/CT study that included unenhanced low-dose CT and enhanced full-dose CT for initial staging. Patients who had undergone previous diagnostic CT for initial staging were excluded. For every patient, each modality of PET/CT images was evaluated by either of 2 pairs of readers, with each pair comprising 1 experienced radiologist and 1 experienced nuclear physician. While evaluating one of the 2 types of PET/CT, the readers were unaware of the results of the other type. Lesion detection, number of sites affected in each anatomic region, and disease stage were assessed. Agreement between techniques was determined by the kappa-statistic, and discordances were studied by the McNemar test. Clinical, analytic, histopathologic, diagnostic CT, and PET data; data from other imaging techniques; and follow-up data constituted the reference standard. RESULTS: For region-based analysis, no significant differences were found between unenhanced low-dose PET/CT and contrast-enhanced full-dose PET/CT, although full-dose PET/CT showed fewer indeterminate findings and a higher number of extranodal sites affected than did low-dose PET/CT. Agreement between the 2 types of PET/CT was almost perfect for disease stage (kappa = 0.92; P < 0.001). CONCLUSION: Our study showed a good correlation between unenhanced low-dose PET/CT and contrast-enhanced full-dose PET/CT for lymph node and extranodal disease in lymphomas, suggesting that unenhanced low-dose PET/CT might suffice in most patients as the only imaging technique for the initial staging of lymphomas, reserving diagnostic CT for selected cases.     

基于30 mA管电流低剂量呼吸门控PET/CT扫描条件的建立讨论

目的 通过改善呼吸门控PET/CT（RG PET/CT）的扫描参数（如管电流、呼吸时相数目、呼吸周期等）,拟建立一个低辐射剂量且图像质量适于临床的扫描条件。 方法 对26例有18F-FDG摄取的肺结节患者行1个床位的低剂量RG PET/CT（30 mA,1min/时相）,评估其辐射剂量,并对比其与常规PET/CT（120 mA,2 min/床位）的图像质量（如均匀性、噪声、视觉评价）的差别。此外,通过模拟不同呼吸周期探讨其与辐射剂量间的关系。 结果 1个PET床位的低剂量RG PET/CT的有效吸收剂量可降至4.88~7.69 mSv[平均（5.68±0.83）mSv],且其PET图像信噪比与常规剂量时相比无明显差异,低剂量CT图像的均匀性在可接受范围（< 5 HU）,噪声较高,视觉评价肺结节特性在某些时相优于常规剂量CT。受检者的呼吸周期与辐射剂量呈正相关。 结论 基于30 mA管电流、6个呼吸时相、1 min/时相、平静呼吸下的RG PET/CT的图像质量能满足肺结节特性观测及肿瘤放疗生物靶区勾画等临床应用,且辐射剂量大幅减低。     

Non-enhanced CT versus contrast-enhanced CT in integrated PET/CT studies for nodal staging of rectal cancer

Purpose The purpose of the present study was to determine the diagnostic accuracy of non-enhanced CT and contrast-enhanced CT in integrated PET/CT studies for preoperative nodal staging of rectal cancer. Methods Retrospective analysis was performed in 53 patients with pathologically proven rectal cancer who had been referred for preoperative staging. All patients underwent integrated PET/CT consisting of non-enhanced and contrast-enhanced CT followed by whole-body fluorine-18-fluorodeoxyglucose ([¹⁸F]FDG) PET. Both non-enhanced and contrast-enhanced PET/CT images were evaluated separately by two observers in consensus. The reference standard was histopathologic results. For nodal staging of rectal cancer, we compared diagnostic accuracy on a per-patient basis between the two modalities. Results Nodal staging was correctly determined with non-enhanced studies in 37 patients (70%) and with contrast-enhanced studies in 42 patients (79%). On a per-patient basis, sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of regional lymph node staging were 85%, 68%, 83%, 72%, and 79%, respectively, with contrast-enhanced studies, and 85%, 42%, 73%, 62%, and 70%, respectively, with non-enhanced studies. The difference in the accuracy of nodal staging between the two modalities was not significant (p = 0.063). Compared with non-enhanced studies, contrast-enhanced studies determined more correctly the status of pararectal lymph nodes (p = 0.002), internal iliac lymph nodes (p = 0.004), and obturator lymph nodes (p < 0.0001). Conclusion Contrast-enhanced PET/CT is superior to non-enhanced PET/CT for precise definition of regional nodal status in rectal cancer.     

Respiration artifacts in whole-body 18F-FDG PET/CT studies with combined PET/CT tomographs employing spiral CT technology with 1 to 16 detector rows

Purpose Co-registration accuracy in combined whole-body (WB) PET/CT imaging is impaired by respiration-induced mismatches between the CT and the PET. Furthermore, PET/CT misregistration may bias the PET tracer distribution following CT-based attenuation correction (CT-AC). With the introduction of multi-row CT technology of up to 16 detector rows into PET/CT designs, we investigated the incidence of respiration artifacts in WB PET/CT examinations of patients who were unable to follow any breath-hold instructions.Methods A total of 80 WB studies from six international sites operating PET/CT tomographs with 1-, 2-, 4-, 6-, 8-, and 16-row spiral CT were included. PET/CT examinations were acquired with the patients breathing normally during both the CT and the PET scan, and CT-AC was performed routinely. All studies were anonymized and reviewed independently by three radiologists and three nuclear medicine specialists. We report the frequency and severity of artifacts on CT and PET for the thorax and the abdomen.Results In WB PET/CT imaging of normally breathing patients, significant gains in diagnostic image quality can be expected from employing CT technology with six or more detector rows. In our study, fewer PET images appear distorted than corresponding CT images, which is due to the limited propagation of only mild CT image artifacts after the resampling of the CT-based attenuation map during CT-AC.Conclusion In whole-body PET/CT imaging of normally breathing patients, respiration-induced artifacts are reduced in both magnitude and prominence for PET/CT systems employing CT components of six or more detector rows.     

Baker cyst as seen on a PET/CT scan

We present the case of a 48-year-old woman who had been diagnosed with multiple myeloma a year ago. She had persistent pain in her right knee that she tended to ignore. As part of her follow-up she underwent a PET/CT scan that did not show any metastatic lesions. However, a focal rounded area of FDG uptake behind her right knee showed a fluid density on the CT scan. A presumptive diagnosis of Baker cyst was suggested. Review of her previous MRI report performed at another hospital corroborated this finding.     

Ipilimumab-induced colitis on FDG PET/CT

A 52-year-old woman with metastatic melanoma was treated with ipilimumab. After 2 cycles of treatment, she developed watery diarrhea, sweats, and chills. An FDG PET/CT study demonstrated new FDG-avid (maximum standardized uptake value 15.6) diffuse colonic wall thickening, suggestive of ipilimumab-induced colitis. The patient was treated with systemic steroids, with subsequent resolution of her symptoms. Based on the response to steroids, the diagnosis of ipilimumab-induced enterocolitis was made. Ipilimumab may cause several immune-mediated toxicities, the most common of which is enterocolitis. Physicians interpreting FDG PET/CT examinations of patients treated with ipilimumab should be aware of these FDG-avid immune-mediated toxicities.     

FDG PET/CT findings of a glomangiopericytoma

Glomangiopericytoma (GPC) is a rare vascular neoplasm that arises almost exclusively from the nasal cavity or paranasal sinuses. GPC is also called sinonasal-type hemangiopericytoma, although current nomenclature, as well as classification in a group with myopericytomas, better emphasizes the relatively indolent behavior of this tumor. The authors present the FDG PET/CT findings of GPC in a 53-year-old with symptoms of nasal congestion and facial pressure. CT and MRI showed a nasal mass to extend along the sphenoid ridge from the posterior nasal cavity into the posterior nasopharynx. PET showed the mass to have uniformly low-grade FDG hypermetabolism. Pathologic examination of the surgical specimen showed classic features of GPC.     

PET and PET/CT in endocrine tumours

Functional information provided by PET tracers together with the superior image quality and the better data quantification by PET technology had a changing effect on the significance of nuclear medicine in medical issues. Recently introduced hybrid PET/CT systems together with the introduction of novel PET radiopharmaceuticals have contributed to the fact that nuclear medicine has become a growing diagnostic impact on endocrinology. In this review imaging strategies, different radiopharmaceuticals including the basic mechanism of their cell uptake, and the diagnostic value of PET and PET/CT in endocrine tumours except differentiated thyroid carcinomas will be discussed.     

PET and PET/CT in pediatric oncology

18F-fluorodeoxyglucose positron emission tomography (FDG-PET) and FDG-PET/computed tomography (CT) are becoming increasingly important imaging tools in the noninvasive evaluation and monitoring of children with known or suspected malignant diseases. In this review, we discuss the preparation of children undergoing PET studies and review radiation dosimetry and its implications for family and caregivers. We review the normal distribution of 18F-fluorodeoxyglucose (FDG) in children, common variations of the normal distribution, and various artifacts that may arise. We show that most tumors in children accumulate and retain FDG, allowing high-quality images of their distribution and pathophysiology. We explore the use of FDG-PET in the study of children with the more common malignancies, such as brain neoplasms and lymphomas, and the less-common tumors, including neuroblastomas, bone and soft-tissue sarcomas, Wilms' tumors, and hepatoblastomas. For comparison, other PET tracers are included because they have been applied in pediatric oncology. Multiple multicenter trials are underway that use FDG-PET in the management of children with neoplastic disease; these studies should give us greater insight into the impact FDG-PET can make in their care. PET is emerging as an important diagnostic imaging tool in the evaluation of pediatric cancers. The recent advent of dual-modality PET-computed tomography (PET/CT) imaging systems has added unprecedented diagnostic capability by revealing the precise anatomical localization of metabolic information and metabolic characterization of normal and abnormal structures. The use of CT transmission scanning for attenuation correction has shortened the total acquisition time, which is an especially desirable attribute in pediatric imaging. Moreover, expansion of the regional distribution of the most common PET radiotracer, FDG, and the introduction of mobile PET units have greatly increased access to this powerful diagnostic imaging technology. Here, we review the clinical applications of PET and PET/CT in pediatric oncology. General considerations in patient preparation and radiation dosimetry will be discussed.