18-Fluorodeoxyglucose positron emission tomography has limited sensitivity for colonic adenoma and early stage colon cancer

Combined SUVmax and localized colonic wall thickening parameters to identify high-risk lesions from incidental focal colorectal 18F-FDG uptake foci

Objective

To evaluate the detection ability of 18F-FDG PET/CT for identifying high-risk lesions (high-risk adenomas and adenocarcinoma) from incidental focal colorectal 18F-FDG uptake foci combining maximum standard uptake value (SUVmax) and localized colonic wall thickening (CWT). The secondary objective was to investigate the factors of missed detection of high-risk adenomas by 18F-FDG PET/CT.

Patients and methods

A total of 6394 patients who underwent 18F-FDG PET/CT in our hospital from August 2019 to December 2021 were retrospectively analysed, and 145 patients with incidental focal colorectal 18F-FDG uptake foci were identified. The optimal cut-off value of SUVmax for 18F-FDG PET/CT diagnosis of high-risk lesions was determined by receiver operating characteristic (ROC) curves. SUVmax and localized CWT were combined to identify high-risk lesions from incidental focal colorectal 18F-FDG uptake foci. The characteristics of incidental adenomas detected and high-risk adenomas missed by 18F-FDG PET/CT were compared.

Results

Of the 6394 patients, 145 patients were found to have incidental focal colorectal FDG uptake foci (2.3%), and 44 patients underwent colonoscopy and pathological examination at the same time. In fact, 45 lesions, including 12 low-risk lesions and 33 high-risk lesions (22 high-risk adenomas, 11 adenocarcinoma), were found by colonoscopy. The area under the ROC curve of SUVmax for low-risk lesions and high-risk lesions was 0.737, and the optimal cut-off value was 6.45 (with a sensitivity of 87.9% and specificity of 58.3%). When SUVmax ≥6.45, the combination of localized CWT parameters has little influence on the sensitivity and specificity of detection; when SUVmax <6.45, the combination of localized CWT parameters can improve the specificity of detection of high-risk lesions, but the sensitivity has little change. In addition, the size of high-risk adenomas discovered incidentally by 18F-FDG PET/CT was larger than that of high-risk adenomas missed, but there was no significant difference in lesion location, pathological type or intraepithelial neoplasia between the two groups.

Conclusions

The combination of SUVmax and localized CWT parameters of 18F-FDG PET/CT helped identify high-risk lesions from incidental focal colorectal 18F-FDG uptake foci, especially for lesions with SUVmax <6.45. Lesion size may be the only factor in 18F-FDG PET/CT missing high-risk adenomas.

Molecular Imaging and Therapy of Colorectal and Anal Cancer

Colorectal cancer is the cancer with the third highest incidence both in males and females in the USA and is also frequently occurring in other industrialized nations. Anal cancer on the other hand is much rarer, but has a rising incidence, especially in high income nations and with a connection to HIV infections, homosexual men and a younger age of the first sexual encounter. Both have high mortality rates in common and are complex to handle in terms of prevention, staging, treatment and diagnostic of recurrence. This article aims to give an overview about the established diagnostic methods of nuclear medicine, especially sole PET and (contrast enhanced) hybrid imaging with 18F-FDG as tracer for primary staging, restaging, therapy monitoring and radiotherapy planning in current guidelines, with a special focus on the American guidelines of the National Comprehensive Cancer Network for colorectal and anal cancer. There will also be an outlook on potential future adjustments in those leading to a more significant representation of nuclear medicine by giving a synopsis of the available studies and data published in international medical press. New tracers that are still in research stage, progress in the imaging techniques, for example a further establishment of PET/MR hybrid imaging, the use of artificial intelligence and parametric imaging, as well as possible future theranostic applications like c-MET binding peptides will also be shortly discussed.

[Importance of FDG-PET/computed tomography in colorectal cancer]

BACKGROUND

Hybrid imaging FDG PET/CT (¹⁸F‑fluordeoxyglucose positron emission tomography/computed tomography) has gained increasing importance in oncology in recent years.

DIAGNOSIS

A focal increase in FDG uptake in the gastrointestinal tract may be due to colorectal carcinoma. Such a finding requires further clarification.

PRIMARY STAGING

Staging of the primary and locoregional lymph nodes remains a domain of established imaging modalities as FDG PET/CT does not provide a clear additional benefit. Liver metastases can be detected with high sensitivity by FDG PET/CT, but MRI is superior in small lesions.

RADIATION THERAPY PLANNING

So far FDG PET/CT plays a subordinate role in the radiation therapy planning of rectal cancer. However, it can potentially contribute to the optimization of planning target volumes.

THERAPY MONITORING

FDG PET/CT is suitable for monitoring therapy because morphological and metabolic changes of the tumor can be detected in early stages. This enables early detection of nonresponders after beginning neoadjuvant chemoradiation therapy of rectal cancer. FDG PET/CT can also be used for therapy control of liver metastases, especially after local therapeutic procedures.

DETECTION OF RECURRENCE

With clinical suspicion of local recurrence and increased tumor markers, FDG PET/CT is a valuable tool as tumor recurrence can be detected with high sensitivity and specificity.

The ability of positron emission tomography/computed tomography to detect synchronous colonic cancers in patients with obstructive colorectal cancer

Positron emission tomography/computed tomography (PET/CT) is frequently used to detect colorectal cancer. The present retrospective study assessed the ability of PET/CT to identify synchronous colonic lesions in 72 patients with obstructive colorectal cancer. All patients had undergone surgical resection without undergoing preoperative total colonoscopy (TCS) at the Digestive Disease Center (April 2007 to September 2016), and subsequently underwent TCS of the proximal colon within 2 years post-surgery. A total of 11 patients exhibited 18F-fluorodeoxyglucose uptake during PET/CT of the proximal colon (4 invasive cancers, 3 advanced adenomas and 4 false-positive results), and 61 patients had no uptake in the proximal colon. Among these 61 patients, postoperative TCS revealed 2 invasive cancers and 4 advanced adenomas. The sensitivity of PET/CT for detecting synchronous invasive cancers was 66.6% (4/6), with a specificity of 89.4% (59/66), a positive predictive value of 36.4% (4/11), a negative predictive value of 96.7% (59/61), and an accuracy of 87.5% (63/72). Negative PET/CT results indicated a low probability of synchronous lesions in the proximal colon. Thus, PET/CT may be a useful tool for detecting synchronous colonic cancers in patients with obstructive colon cancer.

Efficacy of 18-fluoro deoxy glucose-positron emission tomography computed tomography for the detection of colonic neoplasia proximal to obstructing colorectal cancer

Identification of secondary colonic neoplasia proximal to obstructing colorectal cancer is essential for determining the range of colorectal resection.We examined the accuracy of 18-fluoro deoxy glucose-positron emission tomography (FDG-PET) for detection of colonic neoplasia.We recruited patients with obstructing colorectal cancer from our registry. Preoperative FDG-PET was performed, and the detection rate for colonic neoplasia was estimated. Preoperative colonoscopy or postoperative colonoscopy within a year after operation was employed as the indexed standard.Ninety-three patients were included in this study. Colonic neoplasia proximal to obstruction was confirmed in 83 cases. The sensitivity and positive predictive value of FDG-PET were 25.3% and 77.8%, respectively. The sensitivity was higher in larger lesions (3.2% for <5 mm, 29.4% for 6-10 mm, 45.5% for 11-20 mm, and 71.4% for >21 mm) and in higher pathological grade lesions (14.6% for low-grade adenoma, 38.5% for high-grade adenoma, 66.7% for carcinoma in situ, and 100% for invasive carcinoma). The round shape in PET images was a predictor for neoplasia, with an area under the curve of 0.75293 at an aspect ratio of 1.70.FDG-PET should be used as a screening modality for invasive colorectal cancer (CRC) proximal to obstructing colorectal cancer.

Limited Identification of Dual-time-point Positron Emission Tomography/Computed Tomography in Advanced Colorectal Neoplasms

Objective We investigated whether dual-time-point 18-Fluorodeoxyglucose (¹⁸FDG) positron emission tomography/computed tomography (PET/CT) could improve the positive predictive value for detecting advanced colorectal neoplasms (cancer, adenoma ≥10 mm or adenoma with high-grade dysplasia). Methods We retrospectively searched for consecutive patients with a known primary cancer, who had a colonic ¹⁸FDG uptake incidentally found by PET/CT, followed by colonoscopy between January 2013 and August 2014. The clinical characteristics including the maximum standardized uptake value (SUVmax) were compared between advanced colorectal neoplasms and non-advanced lesions. Results Forty-eight patients had 51 foci with an incidental focal colorectal uptake of ¹⁸FDG. Among these 51 foci, 28 foci were judged as being advanced neoplasms, whereas 23 foci identified as non-advanced lesions. Four cases were missed by PET/CT: two laterally spreading tumors (LSTs) with intramucosal cancer and two severe adenomas (<10 mm). The positive predictive value for the detection of advanced neoplasms was 55%. The per-spot performance of PET/CT showed that SUVmax was significantly higher in advanced neoplasms than in non-advanced lesions for the early-phase (10.1±4.9 vs. 6.5±3.2, p=0.029) and the delayed-phase (12.0±6.0 vs. 7.4±4.0, p=0.022). However, more importantly, there was a significant overlap of the SUVmax and no significant difference was found in the retention index (19.2±20.1 vs. 16.6±29.4, p=0.767). Conclusion Dual-time-point PET/CT was found to have limited impact for identifying advanced colorectal neoplasms in spite of its high sensitivity and it might therefore not be able to identify either LSTs or small advanced neoplasms.

Sensitivity of 2-[18F]fluoro-2-deoxyglucose positron emission tomography for advanced colorectal neoplasms: a large-scale analysis of 7505 asymptomatic screening individuals

BACKGROUND

The sensitivity of 2-[¹⁸F]fluoro-2-deoxyglucose positron emission tomography (FDG-PET) for advanced colorectal neoplasms among healthy subjects is not yet fully understood. The present study aimed to clarify the sensitivity by analyzing large-scale data from an asymptomatic screening population.

METHODS

A total of 7505 asymptomatic screenees who underwent both FDG-PET and colonoscopy at our Cancer Screening Division between February 2004 and March 2013 were analyzed. FDG-PET and colonoscopy were performed on consecutive days, and each examination was interpreted in a blinded fashion. The results of the two examinations were compared for each of the divided six colonic segments, with those from colonoscopy being set as the reference. The relationships between the sensitivity of FDG-PET and clinicopathological features of advanced neoplasms were also evaluated.

RESULTS

Two hundred ninety-one advanced neoplasms, including 24 invasive cancers, were detected in 262 individuals. Thirteen advanced neoplasms (advanced adenomas) were excluded from the analysis because of the coexistence of lesions in the same colonic segment. The sensitivity, specificity, and positive and negative predictive values of FDG-PET for advanced neoplasms were 16.9 % [95 % confidence interval (CI) 12.7-21.8 %], 99.3 % (95 % CI 99.2-99.4 %), 13.5 % (95 % CI 10.1-17.6 %), and 99.4 % (95 % CI 99.3-99.5 %), respectively. The sensitivity was lower for lesions with less advanced histological grade, of smaller size, and flat-type morphology, and for those located in the proximal part of the colon.

CONCLUSIONS

FDG-PET is believed to be difficult to use as a primary screening tool in population-based colorectal cancer screening because of its low sensitivity for advanced neoplasms. Even when it is used in opportunistic cancer screening, the limit of its sensitivity should be considered.

Colonoscopic Findings in Patients With Incidental Colonic Focal FDG Uptake

OBJECTIVE

The purpose of this study was to investigate the nature of FDG-avid and non-FDG-avid lesions detected at colonoscopy in patients presenting with incidental focal colonic FDG uptake at PET/CT.

MATERIALS AND METHODS

Among 9073 patients who underwent PET/CT over a 4-year period, 82 patients without a history of colonic disease had focal colonic FDG uptake and underwent colonoscopy. In consensus, a radiologist and a nuclear physician read images from these PET/CT examinations. They recorded the location of focal FDG uptake in the colon and associated CT abnormalities and measured maximum standardized uptake value (SUVmax) and metabolic volume (MV). Readings were performed twice--first without and second with knowledge of lesion location at colonoscopy. The final diagnosis was based on colonoscopic findings and histopathologic results categorized into benign, premalignant, or malignant.

RESULTS

One hundred seven foci of colonic FDG uptake at PET/CT and 150 lesions at colonoscopy were detected. Among 107 foci of FDG uptake, 65 (61%) corresponded to a lesion at colonoscopy (true-positive findings), and 42 (39%) did not (false-positive findings). Among 150 lesions found at colonoscopy, 85 (57%) were not FDG avid (false-negative findings). The MV of true-positive findings was lower than that of false-positive findings (4.0 ± 0.4 cm(3) vs 6.2 ± 0.7 cm(3); p = 0.006), but SUVmax did not differ (7.4 ± 0.5 vs 7.7 ± 0.5; p = 0.649). Considering the histopathologic categories of the lesions and the false-positive findings, there was no difference in SUVmax (p = 0.103), but MV was lower in premalignant lesions than in false-positive findings (p = 0.005).

CONCLUSION

Focal colonic FDG uptake may indicate the presence of a benign, pre-malignant, or malignant lesion. Subsequent colonoscopy should not be restricted to the colonic site of FDG uptake.

Role of fluorine 18 fluorodeoxyglucose positron emission tomography/computed tomography in gastrointestinal cancers

Fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) has become a routine imaging modality for many malignancies and its use is currently increasing. In the present review article, we will summarize the evidence for FDG-PET/CT use in digestive cancers (excluding neuroendocrine tumours), and review the existing recommendations. While PET/CT is nowadays considered to be an important tool in the initial workup of oesophageal and anal cancers, new data are emerging regarding its use in assessing therapeutic efficacy, radiotherapy treatment planning, and detection of recurrence in case of isolated tumour marker elevation. Moreover, PET/CT may help decision making by detecting distant metastatic sites especially in potentially resectable metastatic colorectal cancer and, to a lesser extent, in localized gastric and pancreatic cancers. Finally, incidental focal colonic FDG uptakes require exploration by colonoscopy, as they are often associated with premalignant or malignant lesions.

Comparing respiratory gated with delayed scans in the detection of colorectal carcinoma hepatic and pulmonary metastases with 18F-FDG PET-CT

PURPOSE

In patients experiencing colorectal carcinoma, exhaustive analysis of indicates extent of hepatic and pulmonary surgery that prolongs survival of patients.

PATIENTS AND METHODS

To localize metastasis, we compared 2 F-FDG PET-CT imaging protocols, early respiratory gated scan, and delayed scan, to standard PET imaging procedure. SUVmax and lesion-to-healthy tissue ratio were measured in 60 pulmonary and 21 hepatic lesions by each of the 2 imaging protocols.

RESULTS

In the liver, metastatic lesion-to-healthy tissue ratios significantly increased on delayed scans as compared with early scans (P < 0.001). Better ratios could not be obtained when using respiratory gated scans, whereas more lesions were detected on delayed scans. In the lungs, metastatic lesion- to-healthy tissue ratio increased significantly on delayed scans for largest lesions (P < 0.001). Ratios were not better when exploring smallest metastatic lesions or when using respiratory gated scans. Factors interfering with F-FDG PET-CT sensitivity are discussed, such as respiratory motion and high FDG physiological uptake in healthy liver parenchyma.

CONCLUSIONS

Our studies indicate that routine acquisitions should use delayed hepatic scans for all patients referred for evaluation, recurrence check, or monitoring of colorectal adenocarcinoma. Delayed pulmonary scans are useful for the largest metastatic lesions and should be used in addition to early scan. In our experience, respiratory gated scans seem to be less convenient because of a low sensitivity in detection, as compared with the delayed technique; in addition, this technique is currently complicated by some technical issues, although these might be overcome with new gated protocols.

Visualization of sialidase activity in Mammalian tissues and cancer detection with a novel fluorescent sialidase substrate

Sialidase removes sialic acid from sialoglycoconjugates and plays crucial roles in many physiological and pathological processes. Various human cancers express an abnormally high level of the plasma membrane-associated sialidase isoform.Visualization of sialidase activity in living mammalian tissues would be useful not only for understanding sialidase functions but also for cancer diagnosis. However, since enzyme activity of mammalian sialidase is remarkably weak compared with that of bacterial and viral sialidases, it has been difficult to detect sialidase activity in mammalian tissues. We synthesized a novel benzothiazolylphenol-based sialic acid derivative (BTP-Neu5Ac) as a fluorescent sialidase substrate. BTP-Neu5Ac can visualize sialidase activities sensitively and selectively in acute rat brain slices. Cancer cells implanted orthotopically in mouse colons and human colon cancers (stages T3-T4) were also clearly detected with BTP-Neu5Ac. The results suggest that BTP-Neu5Ac is useful for histochemical imaging of sialidase activities.

A comparison of positron emission tomography and colonoscopy for the detection of advanced colorectal neoplasms in subjects undergoing a health check-up

Background & Aims

There is no agreement as to whether F-18 fluorodeoxyglucose positron emission tomography and computed tomography (FDG PET/CT) screening for advanced colorectal neoplasms is meaningful. This retrospective study was undertaken to determine whether FDG PET/CT may be a valuable screening tool for the detection of advanced colorectal neoplasms.

Methods

A retrospective review of the records of 1,109 FDG PET/CT scans acquired from January 2007 to December 2011 was performed. Colonoscopy and FDG PET/CT imaging were performed within two days of each other. The results of colonoscopy were taken as the gold standard, either with or without the results of the histopathological examination. An advanced neoplasm was defined as the presence of a malignant tumor, an adenoma ≥1 cm, or histological evidence of high-grade dysplasia or significant villous components.

Results

A total of 36 subjects had advanced colorectal neoplasms detected by colonoscopy (totaling 38 neoplasms). Six of the 38 neoplasms were also detected by FDG PET/CT. The sensitivity, specificity, positive predictive value, negative predictive value, and overall accuracy of FDG PET/CT in the detection of advanced colorectal neoplasms were 15.8% (6/38), 99.1% (1063/1073), 37.5% (6/16), 97.1% (1063/1095), and 96.2% (1069/1111) respectively. The presence of lesions with an endoscopic size ≤1.5 cm (P<0.001) and low-grade dysplasia (P<0.001) were the main predictors of false-negative FDG PET/CT findings.

Conclusions

We conclude that FDG PET/CT screening of advanced colorectal neoplasms is unwarranted, especially in the presence of lesions with an endoscopic size ≤1.5 cm or low-grade dysplasia.

Detectability of colorectal neoplasia with fluorine-18-2-fluoro-2-deoxy-D-glucose positron emission tomography and computed tomography (FDG-PET/CT)

BACKGROUND

The purpose of this study was to analyze the detectability of colorectal neoplasia with fluorine-18-2-fluoro-2-deoxy-D-glucose positron emission tomography/computed tomography (FDG-PET/CT).

METHODS

Data for a total of 492 patients who had undergone both PET/CT and colonoscopy were analyzed. After the findings of PET/CT and colonoscopy were determined independently, the results were compared in each of the six colonic sites examined in all patients. The efficacy of PET/CT was determined using colonoscopic examination as the gold standard.

RESULTS

In all, 270 colorectal lesions 5 mm or more in size, including 70 pathologically confirmed malignant lesions, were found in 172 patients by colonoscopy. The sensitivity and specificity of PET/CT for detecting any of the colorectal lesions were 36 and 98%, respectively. For detecting lesions 11 mm or larger, the sensitivity was increased to 85%, with the specificity remaining consistent (97%). Moreover, the sensitivity for tumors 21 mm or larger was 96% (48/50). Tumors with malignant or high-grade pathology were likely to be positive with PET/CT. A size of 10 mm or smaller [odds ratio (OR) 44.14, 95% confidence interval (95% CI) 11.44-221.67] and flat morphology (OR 7.78, 95% CI 1.79-36.25) were significant factors that were associated with false-negative cases on PET/CT.

CONCLUSION

The sensitivity of PET/CT for detecting colorectal lesions is acceptable, showing size- and pathology-dependence, suggesting, for the most part, that clinically relevant lesions are detectable with PET/CT. However, when considering PET/CT for screening purposes caution must be exercised because there are cases of false-negative results.

Detection of incidental colorectal tumours with 18F-labelled 2-fluoro-2-deoxyglucose positron emission tomography/computed tomography scans: results of a prospective study

AIM

This study assessed the clinical significance of incidental colorectal 2-fluoro-2-deoxyglucose (FDG) uptake using (18) F-FDG positron emission tomography/computed tomography (PET/CT) scans and evaluated the importance of colonoscopy when incidental colorectal FDG uptake was observed.

METHOD

A prospective study was designed and conducted at a single institution over a 2-year period. In patients undergoing PET/CT scans, all with FDG uptake in the colorectum were assigned to have colonoscopy and biopsy. The value of PET/CT scanning was studied by comparison with the colonoscopy and biopsy results.

RESULTS

Among 10,978 PET/CT scans, one or more focal uptakes of FDG in the colorectum were observed in 148 (1.35%) patients. In 136 valid patients, malignant colorectal tumours and polyps were found in 23.5% and 20.5%, respectively,, while the colon in the other 56% was normal. A higher false-positive rate was found in the right colon compared with the distal colorectum (66.2%vs 36.7%, P = 0.004). A significant increase of the maximum standardized uptake (SUVmax) value was found among normal, polyps and cancer groups. Multivariate analysis revealed that SUVmax was the risk factor for predicting colorectal cancer or polyps and FDG uptake in the right colon was a negative predictive factor for finding cancers or polyps.

CONCLUSIONS

Our study proves the necessity of colonoscopy when incidental FDG uptake is found on PET/CT imaging. The false-positive FDG uptake is more commonly observed in the right colon. Although the SUVmax value is higher in cancer patients, a high SUVmax value does not necessarily result in malignancies.

FDG PET and PET/CT for colorectal cancer

The evaluation of patients with known or suspected recurrent colorectal carcinoma is now an accepted indication for positron emission tomography using (18)F-fluorodeoxyglucose (FDG-PET) imaging. PET and CT are complimentary, and therefore, integrated PET/CT imaging should be performed where available. FDG-PET/CT is indicated as the initial test for diagnosis and staging of recurrence, and for preoperative staging (N and M) of known recurrence that is considered to be resectable. FDG-PET imaging is valuable for the differentiation of posttreatment changes from recurrent tumor, differentiation of benign from malignant lesions (indeterminate lymph nodes, hepatic, and pulmonary lesions), and the evaluation of patients with rising tumor markers in the absence of a known source. The addition of FDG-PET/CT to the evaluation of these patients reduces overall treatment costs by accurately identifying patients who will and will not benefit from surgical procedures. This new powerful technology provides more accurate interpretation of both CT and FDG-PET images and therefore more optimal patient care. PET/CT fusion images affect the clinical management by guiding further procedures (biopsy, surgery, and radiation therapy), excluding the need for additional procedures, and changing both inter- and intramodality therapy.

Detection of relevant colonic neoplasms with PET/CT: promising accuracy with minimal CT dose and a standardised PET cut-off

Objective:

To determine the performance of FDG-PET/CT in the detection of relevant colorectal neoplasms (adenomas ≥10 mm, with high-grade dysplasia, cancer) in relation to CT dose and contrast administration and to find a PET cut-off.

Methods:

84 patients, who underwent PET/CT and colonoscopy (n = 79)/sigmoidoscopy (n = 5) for \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\left( {{\hbox{79}} \times {\hbox{6}} + {\hbox{5}} \times {\hbox{2}}} \right)} = {\hbox{484}}$$\end{document} colonic segments, were included in a retrospective study. The accuracy of low-dose PET/CT in detecting mass-positive segments was evaluated by ROC analysis by two blinded independent reviewers relative to contrast-enhanced PET/CT. On a per-lesion basis characteristic PET values were tested as cut-offs.

Results:

Low-dose PET/CT and contrast-enhanced PET/CT provide similar accuracies (area under the curve for the average ROC ratings 0.925 vs. 0.929, respectively). PET demonstrated all carcinomas (n = 23) and 83% (30/36) of relevant adenomas. In all carcinomas and adenomas with high-grade dysplasia (n = 10) the SUV_max was ≥5. This cut-off resulted in a better per-segment sensitivity and negative predictive value (NPV) than the average PET/CT reviews (sensitivity: 89% vs. 82%; NPV: 99% vs. 98%). All other tested cut-offs were inferior to the SUV_max.

Conclusion:

FDG-PET/CT provides promising accuracy for colorectal mass detection. Low dose and lack of iodine contrast in the CT component do not impact the accuracy. The PET cut-off SUV_max ≥ 5 improves the accuracy.

Positron emission tomography for the detection of colorectal adenomas

BACKGROUND

(18)F-fluorodeoxyglucose ((18)F-FDG) positron emission tomography (PET) has been reported to detect colorectal adenomas.

AIMS

This study aimed at evaluating the sensitivity of (18)F-FDG PET with computed tomography image fusion (PET/CT) for detecting colorectal adenomas.

METHODS

We retrospectively compared the results of 92 (18)F-FDG PET/CT studies followed by colonoscopy. Colonoscopy and histology were considered as the gold standard.

RESULTS

One hundred fifty-seven lesions were observed. All the 12 malignancies were identified by (18)F-FDG PET/CT but only 27 out of 119 resected adenomas (sensitivity 22.7%) and none of the hyperplastic polyps were detected. At the univariate and multivariate analyses there was a significant statistical association between adenomas sized more than 10mm, presence of villous component and high-grade dysplasia and the ability of (18)F-FDG PET/CT to detect adenomas. (18)F-FDG PET/CT showed an overall sensitivity of 29.8%, a specificity of 81.1%, a positive predictive value (PPV) of 84.8% and a negative predictive value (NPV) of 24.6% for the neoplastic colorectal lesions globally considered.

CONCLUSION

(18)F-FDG PET/CT has a low sensitivity for detecting adenomas. However, because of the specificity and PPV of the technique for neoplastic colorectal lesions, the presence of a focal colorectal FDG uptake justifies the patient undergoing colonoscopy.

Effect of clinicopathologic factors on visibility of colorectal polyps with FDG PET

OBJECTIVE

The objective of our study was to clarify which clinicopathologic factors affect the FDG PET visibility of colorectal polyps.

MATERIALS AND METHODS

We used statistical methods in a retrospective examination of factors affecting the visibility of 87 colorectal polyps in 50 patients who underwent PET for cancer screening.

RESULTS

PET depicted 37% (32/87) of polyps. Univariate analysis revealed significant associations between polyp visibility and polyp size, histologic grade (p < 0.001 each), type (p = 0.004), and patient age (p = 0.049) but not sex or polyp location. The visualization rate increased with increases in polyp size (< or = 5 mm, 12%; 6-10 mm, 47%; > or = 11 mm, 59%) and severity of dysplasia (indefinite or low-grade dysplasia, 13%; high-grade dysplasia, 67%; polyp with early carcinoma, 75%) and was higher for pedunculated polyps (59%) than for nonpedunculated polyps (27%). Multivariate analysis showed that histologic grade was the strongest factor (p < 0.001) among three independent factors (histologic grade, type, and age). The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy for visualization of high-grade or early carcinoma polyps to be removed were 71%, 87%, 78%, 82%, and 80%. Maximum standardized uptake values did not differ significantly between visualized polyps with indefinite or low-grade dysplasia and visualized polyps with high-grade dysplasia or early carcinoma.

CONCLUSION

Histologic grade is the strongest independent factor in FDG PET visibility of colorectal polyps. FDG PET visibility may be helpful for predicting whether a polyp should be removed or observed. FDG PET findings also may suggest the need to alter the treatment of patients with colorectal polyps.

Positron emission tomography for the diagnosis and management of patients with gastrointestinal malignancies

F-18 fluorodeoxyglucose positron emission tomography (FDG-PET) can play an important role in evaluating patients who have locally advanced diseases and in recurrence detection and restaging in patients who have gastrointestinal tract malignancies. Introduction of an integrated PET/CT system enabled the precise co-evaluation of function and morphology and improved the diagnostic ability of FDG-PET. Application of FDG-PET for treatment response evaluation and prognosis prediction is becoming important. Development of novel PET probes is expected to improve the characterization of individual cancer and to contribute to individualized patient management.

Colorectal tubulovillous adenomas identified on fluoro-2-deoxy-d-glucose positron emission tomography/computed tomography scans

OBJECTIVE

The aim of this retrospective study was to assess the significance of incidental focal colonic lesions on fluoro-2-deoxy-d-glucose positron emission tomography/computed tomography (FDG PET/CT) scans in patients undergoing staging for noncolorectal cancer.

METHOD

Of the 110 patients in our PET/CT database, 10 were found to have abnormally high uptake of tracer in their large bowel.

RESULTS

Seven patients who underwent further endoscopic evaluation of these abnormalities had intermediate to high-risk adenomatous polyps.

CONCLUSION

Benign colonic polyps produce high-intensity focal FDG uptake in large bowel. Endoscopic evaluation is recommended before curative resectional surgery of the presenting cancer where appropriate.

Whole-body PET/CT-colonography: a possible new concept for colorectal cancer staging

BACKGROUND

Colorectal cancer (CRC) is a leading cause of death, and necessitates a conjointly performed staging. Until now, a multi-step-examination including optical colonoscopy, cross-sectional and functional imaging is recommended. However, a single examination for whole-body staging with a dedicated CRC staging protocol is desirable. Thus, we developed and evaluated a combined whole-body PET/CT-colonography protocol for dedicated CRC staging in routine clinical use.

METHODS

We integrated CT-colonography into a whole-body PET/CT protocol to achieve a specific "all-in-one" examination for patients suspected of having CRC. After oral and rectal bowel distension, PET/CT-colonography has been performed in 55 patients. All patients had optical colonoscopy one day before PET/CT. PET/CT data sets were evaluated concerning detection and evaluation of colorectal tumour sites, lymph nodes and distant metastases; these results were compared to the results of CT-colonography alone. Surgical resection and/or biopsy served as standards of reference in all patients.

RESULTS

All examinations were fully diagnostic and well tolerated by the patients. PET/CT-colonography showed highly accurate results for overall TNM-evaluation and was significantly more accurate than CT-colonography alone.

CONCLUSIONS

Staging patients with whole-body PET/CT-colonography is technically feasible and accurate. Patients with incomplete colonoscopy or potential synchronous bowel lesions might benefit from this approach.

Advances in metabolic imaging for surgical oncology

This review focuses on several aspects of molecular imaging. First, current positron emission tomography (PET)/CT scanner technology and several novel imaging techniques that are being developed are briefly discussed. Next, current clinical indications for (18)F FDG PET and PET/CT that are relevant to the surgical oncologist are discussed. Finally, advances in molecular imaging that may herald the next generation of PET radiotracers beyond (18)F FDG are reviewed.

PET/CT colonography in patients with colorectal polyps: a feasibility study

PURPOSE

To examine: (1) the feasibility of PET/CT colonography (PET/CTc) in patients with colorectal polyps; (2) the impact of metabolic information on CTc interpretation and, conversely, the impact of morphological information on PET characterisation of focal colorectal uptake.

METHODS

Ten patients with colorectal polyps underwent PET/CTc, followed within 3 h by therapeutic conventional colonoscopy (CC). A radiologist and a nuclear medicine physician analysed the PET/CTc images. The agreement of morphological and metabolic information in the colon and rectum was evaluated. The sensitivity and specificity of PET, CT and PET/CT were calculated for colorectal polyps.

RESULTS

Seventeen polypoid lesions were identified at CC: six< or =5 mm, six between 6 and 9 mm, and five > or =10 mm (four hyperplastic polyps, 11 tubular adenomas, one adenocarcinoma and one submucosal lipoma). A total of 20 scans (supine and prone) were performed in the ten patients: the agreement of morphological and metabolic information was excellent in 17 scans, good in two and moderate in one. PET/CTc showed a sensitivity of 91% for lesions > or =6 mm and a specificity of 100%. The metabolic information did not disclose any further polyps missed on CTc. The morphological information permitted correct classification of all eight instances of focal radiotracer uptake.

CONCLUSION

PET/CTc is a feasible study. Adding a colonographic protocol to PET/CT images seems to allow correct characterisation of all cases of colorectal focal radiotracer uptake. The metabolic information does not seem to increase the accuracy of CTc.

Positron emission tomography in oncology: a review

Positron emission tomography is an evolving imaging tool that is becoming increasingly available for use in clinical practice. This overview will look at the current evidence for the use of positron emission tomography in imaging different tumour types and the different radiotracers that are either available or being evaluated in an investigational setting.

Combined CT colonography and 18F-FDG PET of colon polyps: potential technique for selective detection of cancer and precancerous lesions

OBJECTIVE

The purpose of this study was to determine the feasibility of imaging the colon with fused CT colonography (CTC) and 18F-FDG PET and to correlate the findings with the histologic features of polyps.

SUBJECTS AND METHODS

Eighteen patients with suspected colorectal polyps enrolled in this prospective study. Before colonoscopy, 17 of the patients underwent a combination of FDG PET and CTC. CTC consisted of 4-MDCT merged with PET. PET of the abdomen and pelvis was performed after each CTC scan. One radiologist and one nuclear medicine physician in consensus analyzed PET and CTC fusion data. PET standard uptake value was correlated with the findings at histologic examination of polyps. Patient feasibility was defined as the ability to tolerate prolonged scanning with good colonic distention. Technical feasibility was determined by how closely anatomically matched polyps overlapped on fusion images.

RESULTS

Seventeen of 18 patients tolerated scanning. Eighty-five percent of colon segments were optimally distended. Twenty-three of 27 FDG-avid polyps measuring 10 mm or more had excellent overlap at fusion imaging. PET depicted 23 of 39 premalignant polyps and even showed increased tracer activity associated with four small tubular adenomas (4-6 mm). Sixteen benign polyps (10-25 mm) were not depicted on PET. All nine cases of cancer (tumors measuring 11-60 mm) were detected with both PET and CTC. The standard uptake value of malignant tumors ranged from 4 to 20 (mean, 9). However, six benign flat polyps did not exhibit FDG avidity.

CONCLUSION

The novel combination of CTC and PET was feasible in 17 of 18 patients and allowed excellent image correlation in 23 of 27 proven polyps measuring 10 mm or more on PET-CTC fusion. This technique shows promise in accurate anatomic correlation of both malignant and premalignant lesions evaluated with FDG PET.

Gastrointestinal tract malignancies and positron emission tomography: an overview

(18)F-fluorodeoxyglucose positron emission tomography (FDG-PET) imaging is highly accurate in restaging colorectal cancer, esophageal cancer, and gastrointestinal stromal tumors. Overall, it compares favorably with anatomical imaging in the evaluation of tumor recurrence because metabolic abnormalities usually precede a structural change. Initial staging of these malignancies with PET is best used in patients with locally advanced disease who may benefit from curative resection if distant metastases are not found. It also appears to have great potential in predicting histopathologic response to neoadjuvant therapy and in monitoring the success of radiofrequency ablation and (90)Y microspheres radioembolization soon after intervention. FDG-PET can be used in other gastrointestinal malignancies as a prognostic tool and to detect distant disease but its role has not yet been well defined.