Lee-Shing Chu

Detection of anaerobic odontogenic infections by fluorine-18 fluoromisonidazole.

Odontogenic infections are a potential risk for patients who receive cervicofacial radiotherapy and should be treated before irradiation. Anaerobic microbial infections are the most common causes. This study assessed the value of the hypoxic imaging agent fluorine-18 fluoromisonidazole (FMISO) in detecting anaerobic odontogenic infections. Positron emission tomography (PET) imaging was performed at 2 h after injection of 370 MBq (10 mCi) of FMISO in 26 nasopharyngeal carcinoma patients and six controls with healthy teeth. Tomograms were interpreted visually to identify hypoxic foci in the jaw. All patients received thorough dental examinations as a pre-radiotherapy work-up. Fifty-one sites of periodontitis, 15 periodontal abscesses, 14 sites of dental caries with root canal infection, 23 sites of dental caries without root canal infection, and seven necrotic pulps were found by dental examination. Anaerobic pathogens were isolated from 12 patients. Increased uptake of FMISO was found at 45 out of 51 sites of periodontitis, all 15 sites of periodontal abscess, all 14 sites of dental caries with root canal infection, all seven sites of necrotic pulp and 15 sites of dental caries without obvious evidence of active root canal infection. No abnormal uptake was seen in the healthy teeth of patients or in the six controls. The diagnostic sensitivity, specificity, positive and negative predictive values, and accuracy of FMISO PET scan in detecting odontogenic infections were 93%, 97%, 84%, 99% and 96%, respectively.18F-fluoride ion bone scan done in three patients showed that18F-fluoride ion plays no role in the demonstration of anaerobic odontogenic infection. FMISO PET scan is a sensitive method for the detection of anaerobic odontogenic infections, and may play a complementary role in the evaluation of the dental condition of patients with head and neck tumours prior to radiation therapy.

PET imaging of brain astrocytoma with 1-11C-acetate

PurposeThe purpose of this study was to assess the use of 1-11C-acetate (ACE) as a metabolic tracer for the detection and characterisation of astrocytomas.MethodsPositron emission tomography (PET) studies with ACE and 2-18F-fluoro-2-deoxy-D-glucose (FDG) were performed sequentially in 26 patients with primary astrocytomas. Images were analysed by visual interpretation and determination of the tumour to cortex ratio (T/C ratio) and standardised uptake value (SUV). The tumour uptake was visually scored into three grades as compared with the contralateral cortex: clearly lower (–), almost equal (+) and clearly higher (++).ResultsThere were 85% of astrocytomas with ++ ACE uptake, 15% with + ACE uptake and none with – ACE uptake. Only 19% of astrocytomas had ++ FDG uptake. Thirty-seven percent of high-grade astrocytomas had + FDG uptake and 37% had – FDG uptake. The sensitivity and specificity of the FDG T/C ratio in discriminating high-grade from low-grade astrocytomas were 79% and 100%, respectively, at the cutoff value of 0.75. Using 2.33 as the cutoff value of the ACE T/C ratio, the sensitivity and specificity were 42% and 86%, respectively. FDG was better than ACE in discriminating high-grade from low-grade astrocytomas. T/C ratios and SUVs of FDG uptake of tumours correlated with the histological grades, but those of ACE uptake did not.ConclusionACE appears to be a promising tracer for use in the detection of primary astrocytomas, but is of limited value in the differentiation of high- and low-grade astrocytomas. ACE is complementary to FDG for the diagnosis and characterisation of astrocytoma.

Unilateral Thalamic Hypometabolism in Patients With Temporal Lobe Epilepsy

BACKGROUND/PURPOSE Interictal brain 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET) is useful for localizing the focus of a seizure, and thalamic hypometabolism has been observed in temporal lobe epilepsy (TLE). In this study, we aimed to investigate the prevalence of thalamic hypometabolism and to assess the usefulness of this supplementary finding for lateralizing epileptic foci on FDGPET scans in patients with TLE. METHODS This was a retrospective study of 47 patients who underwent anterior temporal lobectomy to treat medically intractable TLE. Other inclusion criteria were age older than 18 years, preoperative interictal FDG-PET, no structural abnormality (except for mesial temporal sclerosis) on preoperative magnetic resonance imaging, and seizure-free status (Engel class I) for at least 2 years after the operation. The presence and location of hypometabolism on FDG-PET scans were recorded. RESULTS Of the 47 patients examined, 12 were subsequently excluded. Concomitant hypometabolism in both the temporal lobe and the ipsilateral thalamus was observed on FDG-PET scans in seven (20%) of the remaining 35 patients. One patient had thalamic hypometabolism contralateral to the hypometabolic temporal lobe. CONCLUSION Ipsilateral thalamic hypometabolism is a supplementary finding on FDG-PET scans in patients with TLE and can aid in lateralizing epileptic foci during FDG-PET. However, in rare cases, hypometabolism of the contralateral thalamus can occur and cause false lateralization.

The “Fisherman’s Waders” sign in a bone scan of inferior vena cava thrombosis associated with nephrotic syndrome

This paper presents a 61-year-old male patient with nephrotic syndrome, hypercoagulability and IVC thrombosis. Increased soft tissue uptake below the level of the mid chest was seen in his bone scan. The term “Fisherman’s Waders” sign is suggested for this finding, whose recognition may permit the identification of inferior vena cava obstruction in bone scans. The existence of a cavoportal shunt was also confirmed by dynamic scintigraphy.

Added Value of Dual-Time-Point 18F-FDG PET/CT With Delayed Imaging for Detecting Aortic Graft Infection: An Observational Study.

Abstract18F-FDG PET/CT is a promising tool in detecting aortic graft infection. Present study investigated the value of dual-time-point 18F-FDG PET/CT imaging (DTPI) with delayed imaging in assessing aortic graft infection.Twenty-nine patients with suspected aortic graft infection were prospectively enrolled in this DTPI study. Two nuclear medicine physicians read all the images and achieved consensus about the measurement of maximal standardized uptake value (SUVmax) and grading of image quality. The percentages of SUVmax change between initial and delayed images were recorded as retention index (RI); sensitivity, specificity, and accuracy were calculated based on reference standard.All the 5 infected aortic grafts had positive RIs, which were generally higher than that of noninfected grafts. Those noninfected grafts had variable RIs. Seven patients had improved image quality in delayed imaging. DTPI with delayed image detected all the infected grafts with improved specificity (88%) and accuracy (90%), providing conspicuous delineation of the infected graft extent.In conclusion, noninfected aortic grafts had more variable RIs than infected ones. DTPI might be useful for detecting aortic graft infection, improving image quality, and enhancing delineation of the infected aortic grafts.

Superscan in patients with nasopharyngeal carcinoma

Bone scintigraphy plays an important role in the early detection of bone metastases in patients with nasopharyngeal carcinoma and serial scans may aid the clinician to assess the therapeutic response. A superscan is a pattern described as abnormal bone scan, indicating extensive bony metastases associated with various neoplastic diseases. Bone scans from 407 patients with nasopharyngeal carcinoma were reviewed retrospectively. Only six superscans (1.5%) were found. The appearance of a superscan is frequently accompanied by an abnormal titer of serological markers IgG-VCA and IgA-VCA, liver metastases, and poor survival. Although a superscan rarely occurs in nasopharyngeal carcinoma, its appearance may represent a poor prognosis in these patients.

Scintigraphic appearance of parosteal osteosarcoma.

Parosteal osteosarcoma is a rare form of bone tumor. The lesion is usually well differentiated and arises from the bone surface. It has a better prognosis than other osteosarcomas. Although the radiographic features of parosteal osteosarcoma have been well documented, the scintigraphic characteristics of this tumor have not been described in the English literature. The authors show the unique and distinctive scintigraphic appearance of this tumor.

Ga-67 scan in the diagnosis and monitoring of Ludwig's angina.

This report illustrates the findings of serial Ga-67 studies in a case of Ludwig’s angina before and 1, 5, and 9 months after treatment. The initial Ga-67 scan successfully demonstrated the extent of cellulitis involving the bilateral submandibular and neck regions. SPECT excluded possible superior mediastinal invasion by the disease. Abnormal Ga-67 uptake in the right submandibular region and bilateral submandibular and parotid glands persisted for 1 month after treatment despite no clinical evidence of active inflammation. The site of origin of the infection, the right mandibular second molar, remained positive for Ga-67 uptake 5 months after treatment and subsided at 9 months. The Ga-67 scan, planar as well as SPECT, is useful for the early recognition of the extent of infection in Ludwig’s angina, but it has limitations in monitoring the response to antimicrobial treatment. Follow-up Ga-67 studies should be interpreted carefully with other clinical data.

A practical background correction method for an immediately repeated first-pass radionuclide angiography

Background: A satisfactory bolus injection is essential for a successful first‐pass radionuclide angiography (FPRNA). Rescheduling the FPRNA study is usually needed due to high background interference caused by an unsatisfactory bolus injection. We developed a protocol to correct the pre‐existing background activity subsequent to immediately repeating the study. Methods: Seventy‐four consecutive patients who had their bone scan and FPRNA scheduled on the same day were included for analysis. The initial 51 cases constituted the “validation‐only” group. In the other 23 cases, the “validation plus clearance constants” group, a 5‐min dynamic acquisition was performed during the 5‐min equilibrium to obtain the background clearance curve and the clearance constants. For all included 74 cases ejection fraction (EF) analysis was proceeded using the images from the first injection, second injection, and second injection with the corrected background to yield EF1, EF2, and EF2′, respectively. EF2 and EF2′ were then compared to the ejection fraction without background interference, the EF1. Results: For the LV, the mean difference between the EF1 and the uncorrected EF2 (|LVEF1‐LVEF2| in mean ± SD) was 3.1 ± 2.0% and the difference between the EF1 and the corrected EF2′ (|LVEF1‐LVEF2′|) was 1.6 ± 2.1%, while the mean differences for RV are 2.2 ± 1.9% and 1.8 ± 1.8%, respectively. A significant difference (p < 0.05) was observed between the uncorrected and the corrected data for both the LV and RV. Conclusion: In FPRNA, when a bolus injection is immediately readministered, both LVEF and RVEF can be underestimated. With our correction method, the results are superior to those without correction.

Infected Aneurysm of the Abdominal Aorta Demonstrated on Gallium-67 Scintigraphy

Infected aneurysm is defined as a lesion of the arterial wall due to bacterial contamination. The authors show a distinctive scintigraphic appearance of infected aneurysm. A 76-year-old man was admitted to the hospital because of fever and back pain. 67Ga scan showed abnormal concentration in the region corresponding to the anatomical location of the abdominal aorta. Contrast-enhanced CT scan of the mid abdomen revealed an infra-renal aortic aneurysm.