PET in pediatric diseases

Sedation-free pediatric [18F]FDG imaging on totalbody PET/CT with the assistance of artificial intelligence

PURPOSE

While sedation is routinely used in pediatric PET examinations to preserve diagnostic quality, it may result in side effects and may affect the radiotracer's biodistribution. This study aims to investigate the feasibility of sedation-free pediatric PET imaging using ultra-fast total-body (TB) PET scanners and deep learning (DL)-based attenuation and scatter correction (ASC).

METHODS

This retrospective study included TB PET (uExplorer) imaging of 35 sedated pediatric patients under four years old to determine the minimum effective scanning time. A DL-based ASC method was applied to enhance PET quantification. Both quantitative and qualitative assessments were conducted to evaluate the image quality of ultra-fast DL-ASC PET. Five non-sedated pediatric patients were subsequently used to validate the proposed approach.

RESULTS

Comparisons between standard 300-second and ultra-fast 15-second imaging, CT-ASC and DL-ASC ultra-fast 15-second images, as well as DL-ASC ultra-fast 15-second images in non-sedated and sedated patients, showed no significant differences in qualitative scoring, lesion detectability, and quantitative Standard Uptake Value (SUV) (P = ns).

CONCLUSIONS

This study demonstrates that pediatric PET imaging can be effectively performed without sedation by combining ultra-fast imaging techniques with a DL-based ASC. This advancement in sedation-free ultra-fast PET imaging holds potential for broader clinical adoption.

Nuclear Imaging in Pediatric Cardiology: Principles and Applications

Nuclear imaging plays a unique role within diagnostic imaging since it focuses on cellular and molecular processes. Using different radiotracers and detection techniques such as the single photon emission scintigraphy or the positron emission tomography, specific parameters can be assessed: myocardial perfusion and viability, pulmonary perfusion, ventricular function, flow and shunt quantification, and detection of inflammatory processes. In pediatric and congenital cardiology, nuclear imaging can add complementary information compared to other imaging modalities such as echocardiography or magnetic resonance imaging. In this state-of-the-art paper, we appraise the different techniques in pediatric nuclear imaging, evaluate their advantages and disadvantages, and discuss the current clinical applications.

123I-MIBG scintigraphy and 18F-FDG-PET imaging for diagnosing neuroblastoma

BACKGROUND

Neuroblastoma is an embryonic tumour of childhood that originates in the neural crest. It is the second most common extracranial malignant solid tumour of childhood.Neuroblastoma cells have the unique capacity to accumulate Iodine-123-metaiodobenzylguanidine (¹²³I-MIBG), which can be used for imaging the tumour. Moreover, ¹²³I-MIBG scintigraphy is not only important for the diagnosis of neuroblastoma, but also for staging and localization of skeletal lesions. If these are present, MIBG follow-up scans are used to assess the patient's response to therapy. However, the sensitivity and specificity of ¹²³I-MIBG scintigraphy to detect neuroblastoma varies according to the literature.Prognosis, treatment and response to therapy of patients with neuroblastoma are currently based on extension scoring of ¹²³I-MIBG scans. Due to its clinical use and importance, it is necessary to determine the exact diagnostic accuracy of ¹²³I-MIBG scintigraphy. In case the tumour is not MIBG avid, fluorine-18-fluorodeoxy-glucose ((18)F-FDG) positron emission tomography (PET) is often used and the diagnostic accuracy of this test should also be assessed.

OBJECTIVES

PRIMARY OBJECTIVES

1.1 To determine the diagnostic accuracy of ¹²³I-MIBG (single photon emission computed tomography (SPECT), with or without computed tomography (CT)) scintigraphy for detecting a neuroblastoma and its metastases at first diagnosis or at recurrence in children from 0 to 18 years old.1.2 To determine the diagnostic accuracy of negative ¹²³I-MIBG scintigraphy in combination with (18)F-FDG-PET(-CT) imaging for detecting a neuroblastoma and its metastases at first diagnosis or at recurrence in children from 0 to 18 years old, i.e. an add-on test.

SECONDARY OBJECTIVES

2.1 To determine the diagnostic accuracy of (18)F-FDG-PET(-CT) imaging for detecting a neuroblastoma and its metastases at first diagnosis or at recurrence in children from 0 to 18 years old.2.2 To compare the diagnostic accuracy of ¹²³I-MIBG (SPECT-CT) and (18)F-FDG-PET(-CT) imaging for detecting a neuroblastoma and its metastases at first diagnosis or at recurrence in children from 0 to 18 years old. This was performed within and between included studies. ¹²³I-MIBG (SPECT-CT) scintigraphy was the comparator test in this case.

SEARCH METHODS

We searched the databases of MEDLINE/PubMed (1945 to 11 September 2012) and EMBASE/Ovid (1980 to 11 September 2012) for potentially relevant articles. Also we checked the reference lists of relevant articles and review articles, scanned conference proceedings and searched for unpublished studies by contacting researchers involved in this area.

SELECTION CRITERIA

We included studies of a cross-sectional design or cases series of proven neuroblastoma, either retrospective or prospective, if they compared the results of ¹²³I-MIBG (SPECT-CT) scintigraphy or (18)F-FDG-PET(-CT) imaging, or both, with the reference standards or with each other. Studies had to be primary diagnostic and report on children aged between 0 to 18 years old with a neuroblastoma of any stage at first diagnosis or at recurrence.

DATA COLLECTION AND ANALYSIS

One review author performed the initial screening of identified references. Two review authors independently performed the study selection, extracted data and assessed the methodological quality.We used data from two-by-two tables, describing at least the number of patients with a true positive test and the number of patients with a false negative test, to calculate the sensitivity, and if possible, the specificity for each included study.If possible, we generated forest plots showing estimates of sensitivity and specificity together with 95% confidence intervals.

MAIN RESULTS

Eleven studies met the inclusion criteria. Ten studies reported data on patient level: the scan was positive or negative. One study reported on all single lesions (lesion level). The sensitivity of ¹²³I-MIBG (SPECT-CT) scintigraphy (objective 1.1), determined in 608 of 621 eligible patients included in the 11 studies, varied from 67% to 100%. One study, that reported on a lesion level, provided data to calculate the specificity: 68% in 115 lesions in 22 patients. The sensitivity of ¹²³I-MIBG scintigraphy for detecting metastases separately from the primary tumour in patients with all neuroblastoma stages ranged from 79% to 100% in three studies and the specificity ranged from 33% to 89% for two of these studies.One study reported on the diagnostic accuracy of (18)F-FDG-PET(-CT) imaging (add-on test) in patients with negative ¹²³I-MIBG scintigraphy (objective 1.2). Two of the 24 eligible patients with proven neuroblastoma had a negative ¹²³I-MIBG scan and a positive (18)F-FDG-PET(-CT) scan.The sensitivity of (18)F-FDG-PET(-CT) imaging as a single diagnostic test (objective 2.1) and compared to ¹²³I-MIBG (SPECT-CT) (objective 2.2) was only reported in one study. The sensitivity of (18)F-FDG-PET(-CT) imaging was 100% versus 92% of ¹²³I-MIBG (SPECT-CT) scintigraphy. We could not calculate the specificity for both modalities.

AUTHORS' CONCLUSIONS

The reported sensitivities of ¹²³-I MIBG scintigraphy for the detection of neuroblastoma and its metastases ranged from 67 to 100% in patients with histologically proven neuroblastoma.Only one study in this review reported on false positive findings. It is important to keep in mind that false positive findings can occur. For example, physiological uptake should be ruled out, by using SPECT-CT scans, although more research is needed before definitive conclusions can be made.As described both in the literature and in this review, in about 10% of the patients with histologically proven neuroblastoma the tumour does not accumulate ¹²³I-MIBG (false negative results). For these patients, it is advisable to perform an additional test for staging and assess response to therapy. Additional tests might for example be (18)F-FDG-PET(-CT), but to be certain of its clinical value, more evidence is needed.The diagnostic accuracy of (18)F-FDG-PET(-CT) imaging in case of a negative ¹²³I-MIBG scintigraphy could not be calculated, because only very limited data were available. Also the detection of the diagnostic accuracy of index test (18)F-FDG-PET(-CT) imaging for detecting a neuroblastoma tumour and its metastases, and to compare this to comparator test ¹²³I-MIBG (SPECT-CT) scintigraphy, could not be calculated because of the limited available data at time of this search.At the start of this project, we did not expect to find only very limited data on specificity. We now consider it would have been more appropriate to use the term "the sensitivity to assess the presence of neuroblastoma" instead of "diagnostic accuracy" for the objectives.

Clinical applications of PET and PET/CT in pediatric malignancies

The common childhood cancers are leukemia, CNS tumors, lymphomas, soft-tissue tumors (such as rhabdomyosarcoma and fibrosarcoma), neuroblastoma, malignant bone tumors, germ cell tumors with neoplasms of gonads and hepatic tumors. Usually the conventional imaging modalities, such as x-ray, ultrasound, computed tomography (CT) and MRI, are being routinely used for the management of these pediatric malignancies. However, most of these modalities provide structural information and are lacking in functional/metabolic status of these malignancies. Recently, PET and PET/CT have emerged as a functional diagnostic imaging modality for the management of various cancers in adult population. Up to now most of the data published in the literature are on PET alone. PET used in conjunction with CT is useful as it provides an enhanced view of the anatomical details and the malignant focus then can be located with highest accuracy. PET and PET/CT has been found to be useful in, for example, CNS tumors, lymphomas, soft-tissue tumors, neuroblastoma, malignant bone tumors and germ cell tumors. PET/CT has a limited role in early diagnosis, however, it plays an important role in initial staging, treatment response evaluation and detection of metastatic disease in these cancers. Despite the fact that PET/CT has better diagnostic value when compared with conventional imaging, such as CT and MRI, in the management of many pediatric cancers, there are certain limitations. PET/CT has a limited role in detection of lesions smaller than 5 mm, well-differentiated tumors and tumors with low metabolic rate. Many infections and inflammation can lead to false-positive PET/CT results. In the present review we will discuss the various clinical indications of PET and PET/CT in pediatric cancers.

PET imaging for pediatric oncology: an assessment of the evidence

Positron emission tomography (PET) has shown potential benefits when used in therapeutic clinical trials for children with cancer. However, existing trials are limited in scope with small numbers of patients and varied observations, making accurate conclusions about the usefulness of PET scanning impossible. This review examines PET and its applications in pediatric oncology. While evidence is limited, there appears to be a basis for rigorous evaluation of this imaging modality before widespread application without validation from clinical trials.

Positron emission tomography/computed tomography (PET/CT) in children

Although PET imaging has been available for more than two decades, its use has greatly increased lately due to the advent of PET/CT, readily available sources of commercially supplied FDG, and mobile scanners. These features have enabled PET scanning to expand beyond select major university medical centers, with on-site cyclotron facilities to smaller institutions including free- standing children's hospitals. In these settings, imaging is generally limited to FDG, which suffices for most applications, with the majority of studies performed for tumor imaging. FDGI is being used for evaluation of many tumors in children, with its use in lymphoma being the most established. In lymphoma, it has proven quite useful in determining whether active tumor is present in residual masses following treatment, which may otherwise contain only residual fibrous tissue. For brain tumors, FDGI has some relation to tumor grade, although its more important role is distinguishing recurrent or residual tumor from the effects of treatment, particularly radiation necrosis. For neurological evaluation, interictal FDGI is helpful in localizing potential seizure foci for subsequent subdural EEG monitoring. Because of the relatively long uptake time of FDG, true ictal studies cannot be performed with FDG, and these remain within the domain of SPECT imaging of tracers such as Tc-99m HMPAO. Examinations utilizing radiopharmaceuticals other than FDG are significantly more limited in their availability and are limited to PET centers with on-site cyclotrons. However, these additional agents open the door to many additional studies, including more specific tumor-imaging agents of certain tumors such as neuroblastoma. Another neurotransmitter, F-18-fluoro-L-dopa, is of benefit outside of the central nervous system for evaluating infantile hyperinsulism. The use of PET/CT in children is increasing quickly, particularly FDGI imaging of tumors. It is expected that over the next few years, its role will become increasingly better defined.

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.

18F-FDG PET/CT fusion imaging in paediatric solid extracranial tumours

This paper aims at discussing the utility of 18F-FDG PET/CT in the evaluation of paediatric solid extracranial tumours. Following a brief discussion of the basic principles and methodology of PET/CT system, it reviews the main characteristics of the tumours that can be visualised with 18F-FDG PET and presents examples of cases where the combined use of 18F-FDG PET/CT fusion imaging helped in the management of patients. It will also discuss the physiologic biodistribution of 18F-FDG, outlining the normal variants in the paediatric patients that may lead to misinterpretation.

The current status of FDG-PET in tumour volume definition in radiotherapy treatment planning

Positron emission tomography (PET) scan, mainly using 18 F-fluoro-deoxyglucose (FDG) as a tracer, is currently widely accepted as a diagnostic tool in oncology. It may lead to a change in staging and therefore in treatment management. PET can also be used to define the target volume in radiation treatment planning and to evaluate treatment response. In this review, we focused on issues concerning the role of PET in target volume delineation, both for the primary tumour and regional lymph nodes. A literature search was performed using MEDLINE. Furthermore, the following questions were addressed: does PET allow accurate tumour delineation and does it improve the outcome of radiotherapy, in terms of reduced toxicity or a higher tumour control probability? Combined computer tomography (CT) and PET information seems to influence target volume delineation. Using (CT-) PET scan, interobserver variability is being reduced. Only few studies compared delineation based on PET with pathologic examination, showing a complex relation. Preliminary results concerning incorporation of PET information in to target volume delineation varies in different tumour sites. In the field of lung cancer, incorporation of PET seems to improve tumour coverage and spare normal tissues, which may lead to less toxicity or the possibility to escalate dose. In oesophageal cancer and in lymphoma, PET scan can be used to include PET positive lymph nodes in the target volume. In most other tumour sites not enough data are currently available to draw definitive conclusions about the role of PET in radiation treatment planning.