Medhat Osman

Respiratory motion artifacts on PET emission images obtained using CT attenuation correction on PET-CT

Abstract. PET-CT scanners allow generation of transmission maps from CT. The use of CT attenuation correction (CTAC) instead of germanium-68 attenuation correction (Ge AC) might be expected to cause artifacts on reconstructed emission images if differences in respiratory status exist between the two methods of attenuation correction. The aim of this study was to evaluate for possible respiratory motion artifacts (RMA) in PET images attenuation corrected with CT from PET-CT in clinical patients. PET-CT scans were performed using a Discovery LS PET-CT system in 50 consecutive patients (23 males, 27 females; mean age 58.2 years) with known or suspected malignancy. Both CTAC and Ge AC transmission data obtained during free tidal breathing were used to correct PET emission images. Cold artifacts at the interface of the lungs and diaphragm, believed to be due to respiratory motion (RMA), that were seen on CTAC images but not on the Ge AC images were evaluated qualitatively on a four-point scale (0, no artifact; 1, mild artifact; 2, moderate artifact; 3, severe artifact). RMA was also measured for height. Curvilinear cold artifacts paralleling the dome of the diaphragm at the lung/diaphragm interface were noted on 84% of PET-CT image acquisitions and were not seen on the 68Ge-corrected images; however, these artifacts were infrequently severe. In conclusion, RMA of varying magnitude were noted in most of our patients as a curvilinear cold area at the lung/diaphragm interface, but were not diagnostically problematic in these patients.

Prevalence and Patterns of Bone Metastases Detected with Positron Emission Tomography Using F-18 Fdg

Purpose The aim of this retrospective study was to report the prevalence and imaging characteristics of bone metastases detected with F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) and, when possible, compare these findings with the performance of bone scans in the same patients. Methods The reports of 403 patients with histologically proved malignant disease who underwent a PET scan for initial or post-therapeutic staging were reviewed for the presence of possible bone metastases. Based on the final diagnosis confirmed by histopathologic analysis or clinical follow-up, the PET findings of patients with positive bone metastases were evaluated in terms of location, intensity, and patterns. When the PET scan was positive, the PET results were compared with the findings of available bone scans. Results PET studies suggested the presence of bone metastases in 38 patients (9%). No follow-up data were available for 9 patients, and the remaining 29 were evaluated further. Of these patients, 6 had false-positive findings, whereas bone metastatic involvement was clinically confirmed in 23 patients. The primary malignant findings included lung cancer (n = 9), esophageal cancer (n = 3), lymphoma (n = 2), melanoma (n = 2), thyroid cancer (n = 2), breast cancer (n = 1), colon cancer (n = 1), prostate cancer (n = 1), testicular cancer (n = 1), and nasopharyngeal cancer (n = 1). On PET, 5 patients had a solitary metastatic focus (22%), and the remaining 18 patients had multiple lesions (78%). The vertebrae were the most frequently involved bones (74%), followed by pelvic bones (70%), ribs (65%), upper extremities including the scapula (48%), sternum (43%), and lower extremities (43%). The patterns of abnormal uptake were classified into three groups: focal (15 patients, 65%), diffuse (2 patients, 9%), and a mixed pattern (6 patients, 26%). Most of the lesions showed intense abnormal uptake (18 patients, 78%); 5 patients had both intense and moderate FDG uptake. Thirteen of the 23 patients with confirmed bone metastases also had a bone scan, which revealed positive bone disease in all of these patients. However, PET consistently revealed more metastatic foci than did the bone scan on a lesion basis. Conclusions The most frequent pattern of detectable bone metastases with FDG-PET imaging was multiple foci of intense uptake. PET revealed more lesions than did bone scanning, independent of the type of cancer or location of bone involvement, in patients who were accurately diagnosed by FDG-PET imaging.

Central Nervous System Cancers in First-Degree Relatives and Spouses

The increasing incidence of high-grade astrocytomas in the elderly, the associations between these malignancies and environmental factors, and case reports suggesting a familial component to these tumors prompted this study of primary brain tumors in first-degree relatives and spouses. This article describes the findings in 154 patients from 72 consecutive families accrued to the National Familial Brain Tumor Registry from 1991 to 1996. Medical records, pathological slides, and demographic data were reviewed for each identified case. Parents and children were affected in 33 families, siblings in 27, and husbands and wives in 12. The median age of the patients was 50.5 years, 55% were men, and 70% had high-grade astrocytomas. The pattern of tumor occurrence in this population is different from most familial cancers. These tumors did not involve multiple generations or occur at an unusually early age. In addition, the cases tended to cluster in time, with 47% of the familial and 50% of the husband-wife cases occurring within a 5-year span. In families with an affected parent and child, the diagnosis was made in the child before the parent in 45% of the cases. Prognostic factors for these patients appear to be similar to that reported for typical high-grade astrocytomas. This study demonstrates that primary brain tumors can occur in families without a known predisposing hereditary disease. The ages of these patients, the clustering of cases in time, the few affected generations, and the occurrence of brain tumors in spouses suggest that environmental exposures may be important in the etiology of this neoplasm. Although this hypothesis requires further study, it is plausible given the known associations in animals and humans between high-grade astrocytomas and radiation, toxic chemicals, and viruses.

PET/CT: artifacts caused by bowel motion.

Background and aimIn a combined positron emission tomography (PET) and computed tomography (CT) system, the CT images can be used for attenuation correction as well as for image fusion. However, quantitative and qualitative differences have been reported between CT based attenuation corrected PET and conventional transmission scan corrected PET images. The purpose of this study was to investigate potential differences in PET/CT caused by attenuation differences in bowel due to motion. MethodsTwelve patients had PET/CT scans performed using 68Ge transmission and CT attenuation correction methods. Three emission imaging datasets were generated including CT corrected PET, Ge corrected PET, and the difference images (CT corrected PET minus Ge corrected PET). PET difference images were used to identify regions of mismatch and to quantify possible discordance between images by using standardized uptake values (SUVs). Using the Ge corrected PET as the standard, differences in emission images were classified as an overestimation (pattern A) or an underestimation (pattern B) in these difference images. ResultsOne hundred and twenty-three mismatched areas were identified. Among them, overestimated areas in CT corrected image were detected in 36 regions (pattern A), while underestimated areas were evaluated in the remaining 87 regions (pattern B). The mean value of the difference in pattern A (mean±standard deviation=0.84±0.44) was slightly higher than that in pattern B (0.60±0.23), and statistically significant. Six of 36 regions in pattern A had an SUV of greater than 2.5 in CT corrected PET but less than 2.5 in Ge corrected PET; two of 87 regions with pattern B demonstrated an SUV greater than 2.5 in Ge corrected PET and less than 2.5 in CT corrected PET. ConclusionPhysiological bowel motion may result in attenuation differences and subsequent differences in SUVs. Overestimation of fluorodeoxyglucose uptake should not be misinterpreted as disease.

Is there a common SUV threshold in oncological FDG PET/CT, at least for some common indications? A retrospective study

Abstract Purpose. We retrospectively compared the maximum standard uptake value (SUVmax) of FDG PET in four different sites to evaluate whether a common diagnostic SUVmax threshold may exist in these tumor locations. We further postulate that the SUVmax thresholds are higher in thoracic lesions than in extrathoracic lesions. Material and methods. N = 143 patients in four subgroups underwent a FDG PET/CT: a) 42 patients for solitary pulmonary nodules (SPNs) characterization with b) respective mediastinal lymph nodes (LNs), c) 65 patients for LN staging of head and neck cancer, and d) 36 cancer patients diagnosed with adrenal lesions. Receiver operating characteristics of SUVmax values were evaluated. Results. The SUVmax were statistically significantly greater in malignant than in benign lesions. For SPNs and mediastinal LNs, a SUVmax > 3.6 each resulted in a sensitivity of 81% and 87%, and a specificity of 94% and 89%. For cervical LNs and adrenal glands, a SUVmax > 2.2 each showed a sensitivity of 98% and 100%, and a specificity of 83% and 93%. Conclusion. A common SUVmax threshold did not exist in the four studied subgroups. The variable FDG uptake in SPNs and mediastinal LNs are associated with the high prevalence of inflammation/infection within the chest. Similar SUVmax thresholds however may exist for extrathoracic regions where the prevalence of inflammation/infection is low.

Familial Pancreatic Cancer and the Genetics of Pancreatic Cancer

In our current understanding of pancreatic carcinoma, these neoplasms can arise either sporadically or in familial clusters. Extensive chromosome abnormalities are frequent, as is loss of heterozygosity at loci known to contain the tumor suppressor genes DCC, p53, and MTS1. Although the genetic examination of all pancreatic cancers is important, the examination of familial cases is especially useful in that these allow the identification of uniform genetic alterations that are inherited through the germ line. Much additional work needs to be done before the genetic basis of pancreatic cancer is completely understood. Although our knowledge is limited, it is clear that genetic analyses can be used to establish the prognosis for a patient with pancreatic cancer and, it is hoped, will someday be used in the management, treatment, and detection of pancreatic cancer.

F-18 FDG PET/CT characterization of talc pleurodesis-induced pleural changes over time: a retrospective study.

Purpose: The current study characterized pleural changes induced by talc pleurodesis (TP), based on serial positron emission tomography/computer-tomography (PET/CT) with F-18 fluorodeoxyglucose (FDG). Materials and Methods: A total of 8 cancer patients who had both TP and PET/CT and no evidence of active pleural involvement after TP were retrospectively evaluated. Maximum standard uptake values, maximum Hounsfield units (HU), and thickness were followed over time. Results: The 8 patients had 25 PET/CT scans performed in an average of 22 months after TP. An increased FDG uptake was associated with an increase in pleural thickness within 5 months after TP, and both parameters showed statistical significance as compared with findings before TP. After 5 months of TP, the standard uptake value appeared to persist or increase further, and the pleural thickening stabilized. The formation of calcification was a slow process and might lag behind the changes in FDG metabolism and pleural thickness. The HU did not change significantly once pleural calcification had been formed. Conclusions: Knowledge of aforementioned pleural changes may help differentiate TP induced pleural inflammation from pleural malignancy and to avoid false-positive interpretation of FDG PET/CT exams.

Spinal cord metastases from lung cancer: detection with F-18 FDG PET/CT.

Preoperative F-18 FDG PET/CT study in this 57-year-old woman showed an FDG avid lesion in the left upper lung without evidence of lymphadenopathy or distant metastasis. She underwent a left upper lobectomy in June 2005 revealing moderately poorly differentiated adenocarcinoma (pT3N0M0) and subsequent chemotherapy completed December 2005. Nine months later, a left parietal lobe metastatic lesion was surgically resected. A true whole body FDG PET/CT study in November 2006 for restaging demonstrated new FDG avid spinal cord foci, which were highly suspicious for spinal cord metastases; these lesions were confirmed by MRI. Clinically, the patient recently developed back pain without evidence of neurologic deficits.

PET‐CT and the detection of the asymptomatic recurrence or second primary lesions in the treated head and neck cancer patient

The role of follow‐up and the detection of recurrent or new primary disease in cancer management remains to be defined. Specifically, the effectiveness and impact on survival of imaging studies that detects disease before it is symptomatic or noted on exam is unknown.

18F-FDG PET/CT of Patients With Cancer: Comparison of Whole-Body and Limited Whole-Body Technique

OBJECTIVE Use of the routine field of view for whole-body (18)F-FDG PET/CT can lead to underestimation of the true extent of the disease because metastasis outside the typical base of skull to upper thigh field of view can be missed. The purpose of this study was to evaluate the incremental added value of true whole-body as opposed to this limited whole-body PET/CT of cancer patients. MATERIALS AND METHODS True whole-body FDG PET/CT, from the top of the skull to the bottom of the feet, was performed on 500 consecutively registered patients. A log was kept of cases of suspected malignancy outside the typical limited whole-body field of view. Suspected lesions in the brain, skull, and extremities were verified by correlation with surgical pathologic or clinical follow-up findings. RESULTS Fifty-nine of 500 patients had PET/CT findings suggestive of malignancy outside the limited whole-body field of view. Thirty-one of those patients had known or suspected malignancy outside the limited whole-body field of view at the time of the true whole-body study. Among the other 28 patients, follow-up data were not available for two, six had false-positive findings, and new cancerous involvement was confirmed in 20. Detection of malignancy outside the limited whole-body field of view resulted in a change in management in 65% and in staging in 55% of the 20 cases. CONCLUSION Our study showed that 20 of 500 (4.0%) of patients had previously unsuspected malignancy outside the typical limited whole-body field of view. Detection of such malignancy resulted in a change in management in 13 of 500 cases (2.6%). We propose that adopting a true whole-body field of view in the imaging of cancer patients may lead to more accurate staging and restaging than achieved with the routinely used limited whole-body field of view.