PET/CT Fluoroscopy during PET/CT-Guided Interventions: Initial Experience

This study assessed the feasibility and functionality of the use of a high-speed image fusion technology to generate and display positron emission tomography (PET)/computed tomography (CT) fluoroscopic images during PET/CT-guided tumor ablation procedures. Thirteen patients underwent 14 PET/CT-guided ablations for the treatment of 20 tumors. A Food and Drug Administration–cleared multimodal image fusion platform received images pushed from a scanner, followed by near–real-time, nonrigid image registration. The most recent intraprocedural PET dataset was fused to each single-rotation CT fluoroscopy dataset as it arrived, and the fused images were displayed on an in-room monitor. PET/CT fluoroscopic images were generated and displayed in all procedures and enabled more confident targeting in 3 procedures. The mean lag time from CT fluoroscopic image acquisition to the in-room display of the fused PET/CT fluoroscopic image was 21 seconds ± 8. The registration accuracy was visually satisfactory in 13 of 14 procedures. In conclusion, PET/CT fluoroscopy was feasible and may have the potential to facilitate PET/CT-guided procedures.     

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.     

呼气中期屏气CT扫描对PET/CT图像质量和肺组织SUV的影响

目的 探讨呼气中期屏气CT扫描模式对PET/CT图像质量及肺组织SUV的影响.方法 将2010年9月至12月间序列完成18F-FDG PET/CT显像的200例常规受检者纳入研究,其中男120例,女80例,年龄23～87(55.01±11.60)岁.所有受检者按随机数字表法分成2组:平静呼气中期屏气行PET/CT之同机CT采集组[屏气组,男52例,女48例,29～ 83(55.43±10.38)岁]和自由平静呼吸行PET/CT之同机CT采集组[自由呼吸组,男68例,女32例,23 ～ 87(55.68± 12.72)岁],每组各100例.图像分析由核医学科1位资深技师和2位资深医师评判.分析所有PET/CT的PET和CT空间配准、肺底部肺组织SUV和CT图像中肺部呼吸运动伪影等.以PET和CT在同一层面出现膈顶为两者空间配准良好,反之为配准不良.采用SPSS 17.0软件对数据进行统计分析,不同组SUV间差异比较采用两样本t检验或单因素方差分析,率的比较采用x2检验.结果 屏气组同机CT肺组织呼吸伪影发生率(28％,28/100)明显低于自由呼吸组(96％,96/100; x2=98.132,P＜0.01).屏气组PET/CT的PET和CT空间配准良好率(40％,80/200)明显高于自由呼吸组(30％,60/200;x2=4.396,P＜0.05).CT图像上出现膈顶先于PET、PET和CT膈顶位置配准良好和PET图像上出现膈顶先于CT 3种情况的肺底部组织的SUV逐项递增,屏气组(对应的SUVmax分别为0.73±0.28、1.00±0.29和1.60±0.68,SUVmean分别为0.59±0.23、0.81±0.22和1.33±0.34;F=21.93和24.57,均P＜0.01)此现象较自由呼吸组明显(对应的SUVmax分别为0.84±0.36、1.08±0.27和1.16±0.24,SUVmean分别为0.69±0.29、0.85±0.20和0.94±0.24;F=7.23和6.29,均P＜0.01).结论 呼气中期屏气CT扫描简便易行,不增加辐射剂量,可明显降低同机CT呼吸运动伪影发生率,在一定程度上提高PET和CT图像空间配准率.PET和CT失配准膈肌位置不同可导致低估或高估肺组织SUV.     

Attenuation correction of PET images with respiration-averaged CT images in PET/CT.

Attenuation correction (AC) of PET images with helical CT (HCT) in PET/CT matches only the spatial resolution of CT and PET, not the temporal resolution. We therefore proposed the use of respiration-averaged CT (ACT) to match the temporal resolution of CT and PET and evaluated the improvement of tumor quantification in PET images of the thorax with ACT. METHODS: First, we examined 100 consecutive clinical PET/CT studies for the frequency and magnitude of misalignment at the diaphragm position between the HCT and the PET data. Patients were injected with 555-740 MBq of (18)F-FDG and scanned 1 h after injection. The HCT data were acquired at the following settings: 120 kV, 300 mA, pitch of 1.35:1, collimation of 8 x 1.25 mm, and rotation cycle of 0.5 s. Patients were instructed to hold their breath at midexpiration during HCT of the thorax. The PET acquisition was 3 min per bed. Second, we retrospectively analyzed studies of 8 patients (1 with esophageal cancer and 7 with lung cancer). Each study included regular PET/CT followed by 4-dimensional (4D) CT for radiation treatment planning. We compared the results of AC of the PET data with HCT and ACT. There were 13 tumors in these 8 patients. The 4D CT data were acquired at the following settings: 120 kV, 50-150 mA, cine duration of 1 breathing cycle plus 1 s, collimation of 8 x 1.25 mm, and rotation cycle of 0.5 s. The acquisition was taken when the patient was in the free-breathing state. We averaged the 10 phases of the 4D CT data to obtain ACT for AC of the PET data. Both the ACT and the HCT data were used for AC of the same PET data. RESULTS: There was a misalignment between the HCT and the PET data in 50 of 100 patient studies. In 34 studies, the misalignment was greater than 2 cm. In a comparison of HCT and ACT, 5 tumors had differences in standardized uptake values (SUV) between HCT-and ACT-attenuation-corrected PET of less than 20%, and 4 tumors had differences in SUV of more than 50%. The latter 4 tumors were found in the patient with esophageal cancer and in 2 of the patients with lung cancer. The PET data from these 3 patients had a misalignment of 2-4.5 cm relative to the HCT data. Breathing artifacts were significantly reduced by ACT. Seven of the 8 patients had a lower diaphragm position on HCT than on ACT, suggesting that the patients tended to hold a deeper breath during HCT than during ACT. CONCLUSION: The high rate of misalignment suggested a potential mismatch between the HCT and the PET data with the limited-breath-hold CT protocol. In the comparison of HCT and ACT, significant differences (>50%) in SUV were attributable to different breathing states between HCT and PET. The PET data corrected by ACT did not show breathing artifacts, suggesting that ACT may be more accurate than HCT for AC of the PET data.     

Clinical myocardial perfusion PET/CT.

The field of nuclear cardiology is witnessing growing interest in the use of cardiac PET for the evaluation of patients with coronary artery disease (CAD). The available evidence suggests that myocardial perfusion PET provides an accurate means for diagnosing obstructive CAD, which appears superior to SPECT especially in the obese and in those undergoing pharmacologic stress. The ability to record changes in left ventricular function from rest to peak stress and to quantify myocardial perfusion (in mL/min/g of tissue) provides an added advantage over SPECT for evaluating multivessel CAD. There is growing and consistent evidence that gated myocardial perfusion PET also provides clinically useful risk stratification. Although the introduction of hybrid PET/CT technology offers the exciting possibility of assessing the extent of anatomic CAD (CT coronary angiography) and its functional consequences (ischemic burden) in the same setting, there are technical challenges in the implementation of CT-based transmission imaging for attenuation correction. Nonetheless, this integrated platform for assessing anatomy and biology offers a great potential for translating advances in molecularly targeted imaging into humans.     

顽固性癫痫发作间期PET/CT的显像研究

目的探讨顽固性癫痫患者在发作间期PET／CT显像对癫痫灶定位的诊断价值,以指导手术治疗。资料与方法对28例顽固性癫痫患者,行发作间期的^18F—FDG PET／CT显像。对其中的21例癫痫灶较局限的患者行癫痫灶或颞前叶切除,术中行皮层脑电图（ECoG）或深部脑电图（DEEG）描记,以检测其特异性,术后进行随访。结果28例顽固性癫痫患者中,经PET／CT显像有25例显示出低代谢灶,敏感性为89．3％（25／28）。21例手术患者经随访1年以上,癫痫发作消失者18例。结论PET／CT脑显像对癫痫患者的术前定位具有重要价值。     

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.     

Cine CT for attenuation correction in cardiac PET/CT.

In dual-modality PET/CT systems, the CT scan provides the attenuation map for PET attenuation correction. The current clinical practice of obtaining a single helical CT scan provides only a snapshot of the respiratory cycle, whereas PET occurs over multiple respiratory cycles. Misalignment of the attenuation map and emission image because of respiratory motion causes errors in the attenuation correction factors and artifacts in the attenuation-corrected PET image. To rectify this problem, we evaluated the use of cine CT, which acquires multiple low-dose CT images during a respiratory cycle. We evaluated the average and the intensity-maximum image of cine CT for cardiac PET attenuation correction. METHODS: Cine CT data and cardiac PET data were acquired from a cardiac phantom and from multiple patient studies. The conventional helical CT, cine CT, and PET data of an axially translating phantom were evaluated with and without respiratory motion. For the patient studies, we acquired 2 cine CT studies for each PET acquisition in a rest-stress (13)N-ammonia protocol. Three readers visually evaluated the alignment of 74 attenuation image sets versus the corresponding emission image and determined whether the alignment provided acceptable or unacceptable attenuation-corrected PET images. RESULTS: In the phantom study, the attenuation correction from helical CT caused a major artifactual defect in the lateral wall on the PET image. The attenuation correction from the average and from the intensity-maximum cine CT images reduced the defect by 20% and 60%, respectively. In the patient studies, 77% of the cases using the average of the cine CT images had acceptable alignment and 88% of the cases using the intensity maximum of the cine CT images had acceptable alignment. CONCLUSION: Cine CT offers an alternative to helical CT for compensating for respiratory motion in the attenuation correction of cardiac PET studies. Phantom studies suggest that the average and the intensity maximum of the cine CT images can reduce potential respiration-induced misalignment errors in attenuation correction. Patient studies reveal that cine CT provides acceptable alignment in most cases and suggest that the intensity-maximum cine image offers a more robust alternative to the average cine image.     

Deep-inspiration breath-hold PET/CT of the thorax.

The goal of this study was to describe our initial experience with the deep-inspiration breath-hold (DIBH) technique in combined PET/CT of the thorax. This article presents particular emphasis on the technical aspects required for clinical implementation. METHODS: In the DIBH technique, the patient is verbally coached and brought to a reproducible deep inspiration breath-hold level. The first "Hold" period, which refers to the CT session, is considered as the reference. This is followed by 9- to 20-s independent breath-hold PET acquisitions. The goal is to correct for respiratory motion artifacts and, consequently, improve the tumor quantitation and localization on the PET/CT images and inflate the lungs for possible improvement in the detection of subcentimeter pulmonary nodules. A physicist monitors and records patient breathing during PET/CT acquisition using a motion tracker. Patient breathing traces obtained during acquisition are examined on the fly to assess the reproducibility of the technique. RESULTS: Data from 8 patients, encompassing 10 lesions, were analyzed. Visual inspection of fused PET/CT images showed improved spatial matching between the 2 modalities, reduced motion artifacts especially in the diaphragm, and increased the measured standardized uptake value (SUV) attributed to reduced motion blurring, as compared with the standard clinical PET/CT images. CONCLUSION: The practice of DIBH PET/CT is feasible in a clinical setting. With this technique, consistent lung inflation levels are achieved during PET/CT sessions, as judged by both motion tracker and verification of spatial matching between PET and CT images. Breathing-induced motion artifacts are significantly reduced using DIBH compared with free breathing, enabling better target localization and quantitation. The DIBH technique showed an increase in the median SUV by 32.46%, with a range from 4% to 83%, compared with SUVs measured on the clinical images. The median percentage reduction in the PET-to-CT lesions' centroids was 26.6% (range, 3%-50%).     

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.     

18F-FDG PET and PET/CT in fever of unknown origin.

Fever of unknown origin (FUO) was originally defined as recurrent fever of 38.3 degrees C or higher, lasting 2-3 wk or longer, and undiagnosed after 1 wk of hospital evaluation. The last criterion has undergone modification and is now generally interpreted as no diagnosis after appropriate inpatient or outpatient evaluation. The 3 major categories that account for most FUOs are infections, malignancies, and noninfectious inflammatory diseases. The diagnostic approach in FUO includes repeated physical investigations and thorough history-taking combined with standardized laboratory tests and simple imaging procedures. Nevertheless, there is a need for more complex or invasive techniques if this strategy fails. This review describes the impact of (18)F-FDG PET in the diagnostic work-up of FUO. (18)F-FDG accumulates in malignant tissues but also at the sites of infection and inflammation and in autoimmune and granulomatous diseases by the overexpression of distinct facultative glucose transporter (GLUT) isotypes (mainly GLUT-1 and GLUT-3) and by an overproduction of glycolytic enzymes in cancer cells and inflammatory cells. The limited data of prospective studies indicate that (18)F-FDG PET has the potential to play a central role as a second-line procedure in the management of patients with FUO. In these studies, the PET scan contributed to the final diagnosis in 25%-69% of the patients. In the category of infectious diseases, a diagnosis of focal abdominal, thoracic, or soft-tissue infection, as well as chronic osteomyelitis, can be made with a high degree of certainty. Negative findings on (18)F-FDG PET essentially rule out orthopedic prosthetic infections. In patients with noninfectious inflammatory diseases, (18)F-FDG PET is of importance in the diagnosis of large-vessel vasculitis and seems to be useful in the visualization of other diseases, such as inflammatory bowel disease, sarcoidosis, and painless subacute thyroiditis. In patients with tumor fever, diseases commonly detected by (18)F-FDG PET include Hodgkin's disease and aggressive non-Hodgkin's lymphoma but also colorectal cancer and sarcoma. (18)F-FDG PET has the potential to replace other imaging techniques in the evaluation of patients with FUO. Compared with labeled white blood cells, (18)F-FDG PET allows diagnosis of a wider spectrum of diseases. Compared with (67)Ga-citrate scanning, (18)F-FDG PET seems to be more sensitive. It is expected that PET/CT technology will further improve the diagnostic impact of (18)F-FDG PET in the context of FUO, as already shown in the oncologic context, mainly by improving the specificity of the method.     

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.     

PET/CT imaging artifacts

The purpose of this paper is to introduce the principles of PET/CT imaging and describe the artifacts associated with it. PET/CT is a new imaging modality that integrates functional (PET) and structural (CT) information into a single scanning session, allowing excellent fusion of the PET and CT images and thus improving lesion localization and interpretation accuracy. Moreover, the CT data can also be used for attenuation correction, ultimately leading to high patient throughput. These combined advantages have rendered PET/CT a preferred imaging modality over dedicated PET. Although PET/CT imaging offers many advantages, this dual-modality imaging also poses some challenges. CT-based attenuation correction can induce artifacts and quantitative errors that can affect the PET emission images. For instance, the use of contrast medium and the presence of metallic implants can be associated with focal radiotracer uptake. Furthermore, the patient's breathing can introduce mismatches between the CT attenuation map and the PET emission data, and the discrepancy between the CT and PET fields of view can lead to truncation artifacts. After reading this article, the technologist should be able to describe the principles of PET/CT imaging, identify at least 3 types of image artifacts, and describe the differences between PET/CT artifacts of different causes: metallic implants, respiratory motion, contrast medium, and truncation.