Amer Shammas

Pediatric FDG PET/CT: Physiologic Uptake, Normal Variants, and Benign Conditions

Positron emission tomography (PET) with 2-[fluorine-18]fluoro-2-deoxy-D-glucose (FDG) is increasingly being used in the evaluation of pediatric oncology patients. However, the normal distribution of (18)F FDG uptake in children is unique and may differ from that in adults. A number of physiologic variants are commonly encountered, including normal physiologic uptake in the head and neck, heart, breast, thymus, liver, spleen, gastrointestinal tract, genital system, urinary collecting system, bone marrow, muscles, and brown adipose tissue. Benign lesions with increased (18)F FDG uptake are also frequently seen and can be misinterpreted as malignancies. In addition, the use of combined PET/computed tomographic (CT) scanners is associated with pitfalls and artifacts such as attenuation correction and misregistration. Proper interpretation of pediatric (18)F FDG PET/CT studies requires knowledge of the normal distribution of (18)F FDG uptake in children, as well as of the aforementioned physiologic variants, benign lesions, and PET/CT-related artifacts. Knowing these potential causes of misinterpretation can increase accuracy in PET image interpretation, decrease the number of unnecessary follow-up studies or procedures, and improve patient treatment.

Cystic Fibrosis: Detecting Changes in Airway Inflammation with FDG PET/CT

PURPOSE To determine if fluorine 18 fluorodeoxyglucose (FDG) positron emission tomographic (PET)/computed tomographic (CT) imaging can depict a treatment effect from intravenous antibiotics for pulmonary exacerbation in cystic fibrosis (CF). MATERIALS AND METHODS The study was approved by the institutional review board of the Hospital for Sick Children and by Health Canada. Consent was obtained from all subjects. Patients with CF who were between 6 and 18 years of age and were admitted for a pulmonary exacerbation were eligible for the study. FDG PET/CT examinations (with low-dose CT) were performed on days 1 and 14 of admission (±72 hours). PET activity was quantified by using standardized uptake values (SUVs) through assessment of background activity (mean SUV [SUV(mean)]) and superimposed focal uptake (maximum SUV [SUV(max)]) for each lung zone. CT studies were scored by using the CF-CT model. SUVs from pre- and posttherapy studies were compared by using paired t tests. Unpaired t tests were used to compare data in patients with CF and data in 10 control subjects. RESULTS Twenty patients with CF were enrolled. Antibiotic therapy resulted in a significant decrease in SUV(max) (mean difference, 2.3 ± 2.1 [standard deviation], P < .0001). Pretherapy SUV(max) and SUV(mean) and posttherapy SUV(max) were significantly different from those in control subjects. The change in SUV(max) and percentage predicted forced expiratory volume in 1 second was negatively correlated. (R = -0.72, P = .004). Overall CF-CT scores significantly correlated with SUV(max) (R = 0.40, P = .01). CONCLUSION FDG PET/CT is a useful tool for detecting inflammatory changes resulting from treatment for pulmonary exacerbations in pediatric patients with CF. Inflammatory changes detected by using FDG PET/CT correlated with lung function, sputum neutrophil counts, and CF-CT scores. Analyzing focal lung inflammation (with SUV(max)) may be a feasible way to measure airway inflammation in patients with CF.

FDG‐PET and magnetoencephalography in presurgical workup of children with localization‐related nonlesional epilepsy

2‐[18F]Fluoro‐2‐deoxy‐d‐glucose positron emission tomography (FDG‐PET) and magnetoencephalography (MEG) may assist in identifying the epileptogenic zone in children with nonlesional localization‐related epilepsy. The aim of this study was to evaluate sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of FDG‐PET, MEG, FDG‐PET + MEG, and FDG‐PET/MEG in children with nonlesional localization‐related epilepsy.

Brown adipose tissue 18F-FDG uptake in pediatric PET/CT imaging

Positron emission tomography (PET) using [F-18]2-fluoro-2-deoxyglucose (FDG) fused with CT (18F-FDG PET/CT) has been widely adopted in oncological imaging. However, it is known that benign lesions and other metabolically active tissues, such as brown adipose tissue (BAT), can accumulate 18F-FDG, potentially resulting in false-positive interpretation. Previous studies have reported that 18F-FDG uptake in BAT is more common in children than in adults. We illustrate BAT FDG uptake in various anatomical locations in children and adolescents. We also review what is known about the effects of patient-related physical attributes and environmental temperatures on BAT FDG uptake, and discuss methods used to reduce BAT FDG uptake on 18F-FDG PET.

Pediatric Nuclear Medicine in Acute Care

Various radiopharmaceuticals are available for imaging pediatric patients in an acute care setting. This article focuses on the common applications used on a pediatric patient in acute care. To confirm the clinical diagnosis of brain death, brain scintigraphy is considered accurate and has been favorably compared with other methods of detecting the presence or absence of cerebral blood flow. Ventilation-perfusion lung scans are easy and safe to perform with less radiation exposure than computed tomography pulmonary angiography and remain an appropriate procedure to perform on children with suspected pulmonary embolism as a first imaging test in a hemodynamically stable patient with no history of lung disease and normal chest radiograph. (99m)Tc pertechnetate scintigraphy (Meckels scan) is the best noninvasive procedure to establish the diagnosis of ectopic gastric mucosa in Meckels diverticulum. Hepatobiliary scintigraphy is the most accurate diagnostic imaging modality for acute cholecystitis. (99m)Tc-dimercaptosuccinic acid scintigraphy is the simplest, and the most reliable and sensitive method for the early diagnosis of focal or diffuse functional cortical damage. Bone scintigraphy is a sensitive and noninvasive technique for the diagnosis of bone disorders such as osteomyelitis and fracture. Of recent, positron emission tomography imaging using (18)F-NaF has been introduced as an alternative to bone scintigraphy. (18)F-fluorodeoxyglucose-positron emission tomography has the potential to replace other imaging modalities, such as the evaluation of fever of unknown origin in pediatric patients, with better sensitivity and significantly less radiation exposure than gallium scan.

The value of 18F‐FDG PET in pediatric patients with post‐transplant lymphoproliferative disorder at initial diagnosis

PTLD is a serious complication of both solid organ and BMT. This study assessed whether 18F‐FDG PET, when added to CT scan, had additional value in the initial evaluation of PTLD in pediatric patients and whether PET/CT at baseline can reliably guide biopsy. This retrospective study evaluated 34 consecutive pediatric patients (14 female), aged 3.5–17.0 yr (mean age: 9.9 yr, s.d.: 4.9 yr), who had undergone 18F‐FDG PET/CT from May 2007 to December 2014 at initial diagnosis of PTLD following heart (n = 13), lung (n = 8), kidney (n = 4), liver (n = 3), liver and bowel (n = 3), and bone marrow (n = 3) transplantation. PTLD was diagnosed histopathologically in 33 patients and was based on clinical findings, elevated EBV, and imaging and follow‐up results in one patient. On lesion‐based analysis, 18F‐FDG PET showed more lesions than conventional CT scan (168 vs. 134), but CT revealed 22 lesions negative on PET. On per patient analysis, PET detected more lesions in 13 patients, CT identified more abnormalities in seven, and both showed the same number of lesions in 14. Adding 18F‐FDG PET to CT scans upstaged the disease in seven patients (20.5%). A combination of 18F‐FDG PET and CT was also useful in guiding biopsy, being positive in 36 of 39 samples (92.3%). These findings indicated that 18F‐FDG PET and CT are complementary at initial staging of pediatric PTLD and that 18F‐FDG PET/CT scanning can guide biopsies.

Neuroendocrine tumor in liver with positive ACTH receptor: a case report.

A rare case of possible primary ectopic adrenocorticotropic hormone (ACTH)-producing tumor in the liver mimicking a liver hemangioma is reported. A 9-year-old boy, with Cushing syndrome, was referred for the assessment of ectopic ACTH-producing tumor. Ultrasound, CT scan, and MRI of the abdomen revealed a liver lesion suggestive of a hemangioma. 111In-octreotide scintigraphy revealed focal activity in the liver, indicative of a somatostatin-positive lesion. 99mTc-labeled RBC scintigraphy was negative for hemangioma. After surgical resection of the tumor, the cortisol level converted to a normal range indicative of a rare possible primary ACTH-producing tumor in the liver, which was confirmed by histopathology.

Computed Tomography Angiography in Acute Gastrointestinal and Intra-abdominal Bleeding in Children: Preliminary Experience

Acute gastrointestinal (GI) and intra-abdominal bleeding from different etiologies is a medical emergency with a significant morbidity and mortality. Fast detection and localization of the bleeding site are essential for effective hemostatic therapy [1]. In children with a GI bleed, it is important to assess the hemodynamic status and to establish the site of bleeding and a differential diagnosis according to the presentation and the age of the patient [2]. In trauma, a prompt diagnosis of a bleeding site can improve the efficacy of patient management [3]. Rupture and bleeding are a known presentation of solid tumours, including hepatoblastoma and hepatocellular carcinoma [4]. The most frequent causes of GI and intra-abdominal bleeding in children are shown in Table 1. The initial approach to a patient with GI bleed is endoscopy, which can be diagnostic and therapeutic. If it fails, then catheter angiography is considered. With trauma or tumoural bleeding, angiography is considered according to the diagnostic imaging workup and clinical picture. Pediatric angiography has recognized complications, which nowadays are less frequent due to the improvement in the equipment and the use of ultrasound (US) for vascular access [5]. In taking this into consideration, it is important to adequately select the group of patients that will benefit from a conventional catheter angiography in this particular clinical setting. Computed tomography angiography (CTA) has an emerging role in the diagnosis of acute GI bleed in adults. Its

Influence of Chronic Recurrent Multifocal Osteomyelitis (CRMO) On Densitometry Measurements Obtained by Dual X-Ray Absorptiometry

The incidence of detecting focal chronic recurrent multifocal osteomyelitis (CRMO) lesions on dual-energy x-ray absorptiometry (DXA), and the effect of these lesions on DXA bone mineral density (BMD), bone mineral content (BMC), and their associated Z-scores were retrospectively reviewed. Materials and Methods. The study included 22 patients (14 females, 8 males; median age of 13 years) with CRMO and in whom a total body less head (TBLH) and lumbar spine DXA scan had been obtained. Whole-body bone scintigraphy and MRI were used as the reference standards. Sites involved with CRMO were subsequently detected and DXA measurements were re-measured after removing the sclerotic lesions from the analysis. Results. In total, sclerotic CRMO lesions were detected in 15 of the 22 patients (68%) by DXA, although the number of lesions detected (on a per-lesion analysis) was much less (i.e. 29 of 129 lesions; 19.4%) when compared to MRI and/or bone scintigraphy. Larger lesions had a greater impact on the derived BMD/BMC measurements, and changed the diagnosis in one patient from having normal to abnormal DXA results based on the final Z-score. Discussion. CRMO lesions detected on DXA examinations should be regarded as a potential source of error. Careful inspection and re-quantification of the BMD, BMC and associated Z-score after applying an appropriate correction should be considered in patients with large CRMO lesions identified on DXA examinations.

Review: The Role of Radiolabeled DOTA-Conjugated Peptides for Imaging and Treatment of Childhood Neuroblastoma

BACKGROUND Childhood neuroblastoma is a heterogenous disease with varied clinical presentation and biology requiring different approaches to investigation and management. Metaiodobenzylguanidine (MIBG) is an essential component of metastatic staging for neuroblastoma and has been used as a treatment strategy for relapsed and refractory neuroblastoma. However, as 10% of children with neuroblastoma will have 123I-MIBG non-avid imaging and up to 60% with relapsed and refractory neuroblastoma will require further treatment with 131I-MIBG, alternative radioisotopes have been investigated for imaging and treatment. Neuroblastoma tumors express mostly somatostatin receptor- 2 (SSTR2) that can be targeted by somatostatin analogues including DOTA-conjugated peptides e.g. DOTATATE, DOTATOC. OBJECTIVES This review summarizes the rationale, utility and experience of DOTA-conjugated peptides in imaging and treatment of childhood neuroblastoma. RESULTS AND CONCLUSIONS Radiolabeled DOTA-peptides are used routinely in adults to image neuroendocrine tumors and have potential to be used to image and treat neuroblastoma. 68Ga-DOTATATE PET/CT has been shown to have better sensitivity, quicker clearance and administration times, reduced radiation exposure and limited toxicity compared to 123I-MIBG. Therapeutic studies of peptide receptor radionuclides e.g. 177Lu-DOTATATE in patients with relapsed neuroblastoma have used 68Ga- DOTATATE PET/CT to determine eligibility for therapy. Further studies would need to investigate appropriate indications, timings, scoring and clinical significance of radiolabeled DOTA-peptide conjugated PET/CT imaging in childhood neuroblastoma.