Advances in positron emission tomography imaging for the GI tract

Imaging and biopsy of HIV-infected individuals undergoing analytic treatment interruption

Background

HIV persistence during antiretroviral therapy (ART) is the principal obstacle to cure. Lymphoid tissue is a compartment for HIV, but mechanisms of persistence during ART and viral rebound when ART is interrupted are inadequately understood. Metabolic activity in lymphoid tissue of patients on long-term ART is relatively low, and increases when ART is stopped. Increases in metabolic activity can be detected by ¹⁸F-fluorodeoxyglucose Positron Emission Tomography (FDG-PET) and may represent sites of HIV replication or immune activation in response to HIV replication.

Methods

FDG-PET imaging will be used to identify areas of high and low metabolic uptake in lymphoid tissue of individuals undergoing long-term ART. Baseline tissue samples will be collected. Participants will then be randomized 1:1 to continue or interrupt ART via analytic treatment interruption (ATI). Image-guided biopsy will be repeated 10 days after ATI initiation. After ART restart criteria are met, image-guided biopsy will be repeated once viral suppression is re-achieved. Participants who continued ART will have a second FDG-PET and biopsies 12–16 weeks after the first. Genetic characteristics of HIV populations in areas of high and low FDG uptake will be assesed. Optional assessments of non-lymphoid anatomic compartments may be performed to evaluate HIV populations in distinct anatomic compartments.

Anticipated results

We anticipate that PET standardized uptake values (SUV) will correlate with HIV viral RNA in biopsies of those regions and that lymph nodes with high SUV will have more viral RNA than those with low SUV within a patient. Individuals who undergo ATI are expected to have diverse viral populations upon viral rebound in lymphoid tissue. HIV populations in tissues may initially be phylogenetically diverse after ATI, with emergence of dominant viral species (clone) over time in plasma. Dominant viral species may represent the same HIV population seen before ATI.

Discussion

This study will allow us to explore utility of PET for identification of HIV infected cells and determine whether high FDG uptake respresents areas of HIV replication, immune activation or both. We will also characterize HIV infected cell populations in different anatomic locations. The protocol will represent a platform to investigate persistence and agents that may target HIV populations.

Study protocol registration

Identifier: NCT05419024.

The Role of Positron Emission Tomography in Clinical Management of Intraductal Papillary Mucinous Neoplasms of the Pancreas

Intraductal papillary mucinous neoplasms (IPMNs) of the pancreas represent a heterogeneous group of tumors, increasingly diagnosed in clinical practice. An early differential diagnosis between malignant and benign lesions is crucial to patient management and the choice of surgery or observation. The therapeutic approach is currently based on a patient’s clinical, biochemical, and morphological characteristics. The latest published International Consensus Guidelines (ICG) make no mention of the role of metabolic assessments of IPMNs. The aim of this study was to review the current literature, examining the role of 18-fluorodeoxyglucose (FDG) positron emission tomography (PET) in IPMN management. An extensive literature review was conducted according to the 2009 Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, and 10 articles were analyzed in detail, focusing on the value of PET as opposed to other standard imaging criteria. Data were retrieved on 419 patients. The 18-FDG-PET proved more sensitive, specific, and accurate than the ICG criteria in detecting malignant IPMNs (reaching 80%, 95%, and 87% vs. 67%, 58%, and 63%, respectively). Metabolic assessments may be used as an additional tool for the appropriate management of patients with doubtful imaging findings.

18-fluorodeoxyglucose positron emission tomography enhances computed tomography diagnosis of malignant intraductal papillary mucinous neoplasms of the pancreas

OBJECTIVE

To assess the reliability of 18-fluorodeoxyglucose positron emission tomography (18-FDG PET) in distinguishing benign from malignant intraductal papillary mucinous neoplasms (IPMNs) of the pancreas and its contribution to surgical decision making.

SUMMARY BACKGROUND DATA

Pancreatic IPMNs are increasingly recognized, often as incidental findings, especially in people over age 70 and 80. Computed tomography (CT) and magnetic resonance (MR) are unreliable in discriminating a benign from a malignant neoplasm. 18-FDG PET as imaging procedure based on the increased glucose uptake by tumor cells has been suggested for diagnosis and staging of pancreatic cancer.

METHODS

From January 1998 to December 2005, 64 patients with suspected IPMNs were prospectively investigated with 18-FDG PET in addition to conventional imaging techniques [helical-CT in all and MR and magnetic resonance cholangiopancreatography (MRCP) in 60]. 18-FDG PET was analyzed visually and semiquantitatively using the standard uptake value (SUV). The validation of the diagnosis was made by a surgical procedure (n = 44), a percutaneous biopsy (n = 2), main duct cytology (n = 1), or follow-up (n = 17). Mean and median follow-up times were 25 and 27.5 months, respectively (range, 12-90 months).

RESULTS

Twenty-seven patients (42%) were asymptomatic. Forty-two patients underwent pancreatic resection, 2 palliative surgery, and 20 did not undergo surgery. An adenoma was diagnosed in 13 patients, a borderline tumor in 8, a carcinoma in situ in 5, and an invasive cancer in 21; in 17 patients a tumor sampling was not performed and therefore the histology remained undetermined. Positive criteria of increased uptake on 18-FDG PET was absent in 13 of 13 adenomas and 7 of 8 borderline IPMNs, but was present in 4 of 5 carcinoma in situ (80%) and in 20 of 21 invasive cancers (95%). Conventional imaging technique was strongly suggestive of malignancy in 2 of 5 carcinomas in situ and in 13 of 21 invasive carcinomas (62%). Furthermore, conventional imaging had findings that would be considered falsely positive in 1 of 13 adenomas (8%) and in 3 of 8 borderline neoplasms (37.5%). Therefore, positive 18-FDG PET influenced surgical decision making in 10 patients with malignant IPMN. Furthermore, negative findings on 18-FDG PET prompted us to use a more limited resection in 15 patients, and offered a follow-up strategy in 18 patients (3 positive at CT scan) for the future development of a malignancy.

CONCLUSIONS

18-FDG PET is more accurate than conventional imaging techniques (CT and MR) in distinguishing benign from malignant (invasive and noninvasive) IPMNs. 18-FDG PET seems to be much better than conventional imaging techniques in selecting IPMNs patients, especially when old and asymptomatic, for surgical treatment or follow-up.

Abdominal positron-emission tomography lesions with increased standardized uptake values correlate with intraoperative findings

BACKGROUND

The reporting of standardized uptake value (SUV) on fluoro-2-deoxy-D-glucose positron-emission tomography (FDG-PET) in colorectal cancer is becoming common practice, but its clinical utility remains to be determined. This study was designed to compare FDG-PET uptake as measured by SUV with operative findings.

METHODS

A colorectal cancer database was queried to identify patients who underwent FDG-PET scans with reported SUVs followed by exploratory laparotomy within 3 months and compare these results to determine FDG-PET sensitivity.

RESULTS

Of 46 patients, 16 (34.8%) were found to be have increased extent of disease intraoperatively than seen on FDG-PET scan. This patient population had a statistically significant decreased mean maximal SUV than the patients whose FDG-PET scan equaled intraoperative findings (P < .025).

CONCLUSIONS

This initial study indicates patients with potentially resectable disease by PET scan but decreased FDG uptake should undergo laparoscopic evaluation before performing laparotomy.

The incremental effect of positron emission tomography on diagnostic accuracy in the initial staging of esophageal carcinoma

BACKGROUND

The purpose of the current study was to assess whether [18F]fluorodeoxyglucose positron emission tomography (FDG-PET) provides incremental value (e.g., additional information on lymph node involvement or the presence of distant metastases) compared with computed tomography (CT) in patients with esophageal carcinoma.

METHODS

The authors examined 149 consecutive patients with thoracic esophageal carcinoma. Eighty-one patients underwent radical esophagectomy without pretreatment, 17 received chemoradiotherapy followed by surgery, 3 underwent endoscopic mucosal resection, and the remaining 48 patients received definitive radiotherapy and chemotherapy. The diagnostic accuracy of FDG-PET and CT was evaluated at the time of diagnosis.

RESULTS

The primary tumor was visualized using FDG-PET in 119 (80%) of 149 patients. Regarding lymph node metastases, FDG-PET had 32% sensitivity, 99% specificity, and 93% accuracy for individual lymph node group evaluation and 55% sensitivity, 90% specificity, and 72% accuracy for lymph node staging evaluation. PET exhibited incremental value over CT with regard to lymph node status in 14 of 98 patients who received surgery: 6 patients with negative CT findings were eventually shown to have lymph node metastases (i.e., they had positive PET findings and a positive reference standard [RS]); 6 patients with positive CT findings were shown not to have lymph node metastases (i.e., they had negative PET findings and a negative RS); and 2 patients were shown to have cervical lymph node metastases in addition to mediastinal or abdominal lymph node metastases. Among the remaining patients, PET showed incremental value over CT with regard to distant organ metastases in six patients. The overall incremental value of PET compared with CT with regard to staging accuracy was 14% (20 of 149 patients).

CONCLUSIONS

FDG-PET provided incremental value over CT in the initial staging of esophageal carcinoma. At present, combined PET-CT may be the most effective method available for the preoperative staging of esophageal tumors.

Value of positron emission tomography in the diagnosis of recurrent oesophageal carcinoma

BACKGROUND

Positron emission tomography (PET) with [18F]fluorodeoxyglucose (FDG) might be useful for staging oesophageal squamous cell carcinoma (SCC). FDG-PET may be more accurate than computed tomography (CT) in diagnosing lymph node metastasis. This retrospective study compared the ability of FDG-PET and CT to diagnose recurrent oesophageal carcinoma.

METHODS

Fifty-five patients with thoracic oesophageal SCC who had undergone radical oesophagectomy were studied. The accuracy of FDG-PET and CT in detecting recurrence during follow-up was calculated using data from the first images generated by either modality that suggested the presence of recurrent disease. Lesions deemed to be equivocal on these scans were considered as positive for recurrence.

RESULTS

Twenty-seven of the 55 patients had recurrent disease in a total of 37 organs. Locoregional recurrence was observed in 19 patients (35 per cent). Distant recurrent disease occurred in 15 patients (27 per cent) in 18 organs. Six patients had recurrence in the liver, four in the lung, six in bone and two in distant lymph nodes. FDG-PET showed 96 per cent sensitivity, 68 per cent specificity and 82 per cent accuracy in demonstrating recurrent disease. The corresponding values for CT were 89, 79 and 84 per cent. The sensitivity of FDG-PET was higher than that of CT in detecting locoregional recurrence, but its specificity was lower because of FDG uptake in the gastric tube and thoracic lymph nodes. In distant organs the sensitivity of PET in detecting lung metastasis was lower than that of CT, but its sensitivity for bone metastasis was higher.

CONCLUSION

FDG-PET has a larger field than CT. Combined PET-CT would appear to be an appropriate modality for the detection of recurrent oesophageal cancer.