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

Molecular Imaging of Innate Immunity and Immunotherapy

The innate immune system plays a key role as the first line of defense in various human diseases including cancer, cardiovascular and inflammatory diseases. In contrast to tissue biopsies and blood biopsies, in vivo imaging of the innate immune system can provide whole body measurements of immune cell location and function and changes in response to disease progression and therapy. Rationally developed molecular imaging strategies can be used in evaluating the status and spatio-temporal distributions of the innate immune cells in near real-time, mapping the biodistribution of novel innate immunotherapies, monitoring their efficacy and potential toxicities, and eventually for stratifying patients that are likely to benefit from these immunotherapies. In this review, we will highlight the current state-of-the-art in noninvasive imaging techniques for preclinical imaging of the innate immune system particularly focusing on cell trafficking, biodistribution, as well as pharmacokinetics and dynamics of promising immunotherapies in cancer and other diseases; discuss the unmet needs and current challenges in integrating imaging modalities and immunology and suggest potential solutions to overcome these barriers.

Role of advanced imaging techniques in the evaluation of oncological therapies in patients with colorectal liver metastases

In patients with colorectal liver metastasis (CRLMs) unsuitable for surgery, oncological treatments, such as chemotherapy and targeted agents, can be performed. Cross-sectional imaging [computed tomography (CT), magnetic resonance imaging (MRI), 18-fluorodexoyglucose positron emission tomography with CT/MRI] evaluates the response of CRLMs to therapy, using post-treatment lesion shrinkage as a qualitative imaging parameter. This point is critical because the risk of toxicity induced by oncological treatments is not always balanced by an effective response to them. Consequently, there is a pressing need to define biomarkers that can predict treatment responses and estimate the likelihood of drug resistance in individual patients. Advanced quantitative imaging (diffusion-weighted imaging, perfusion imaging, molecular imaging) allows the in vivo evaluation of specific biological tissue features described as quantitative parameters. Furthermore, radiomics can represent large amounts of numerical and statistical information buried inside cross-sectional images as quantitative parameters. As a result, parametric analysis (PA) translates the numerical data contained in the voxels of each image into quantitative parameters representative of peculiar neoplastic features such as perfusion, structural heterogeneity, cellularity, oxygenation, and glucose consumption. PA could be a potentially useful imaging marker for predicting CRLMs treatment response. This review describes the role of PA applied to cross-sectional imaging in predicting the response to oncological therapies in patients with CRLMs.

Can Computed Tomography Colonography Replace Optical Colonoscopy in Detecting Colorectal Lesions?: State of the Art

Colorectal cancer is an important cause of morbidity and mortality worldwide. Optical colonoscopy (OC) is widely accepted as the reference standard for the screening of colorectal polyps and cancers, and computed tomography colonography (CTC) is a valid alternative to OC. The purpose of this review was to assess the diagnostic accuracy of OC and CTC for colorectal lesions. A literature search was performed in PubMed, Embase, and Cochrane Library, and 18 articles were included. CTC has emerged in recent years as a potential screening examination with high accuracy for the detection of colorectal lesions. However, the clinical application of CTC as a screening technique is limited because it is highly dependent on the size of the lesions and has poor performance in detecting individual lesions <5 mm or flat lesions, which, although rarely, can have a malignant potential.

PET/CT Integrated With CT Colonography in Preoperative Obstructive Colorectal Cancer by Incomplete Optical Colonoscopy: A Prospective Study

AIM

The aim of this study was to evaluate if integrating whole-body PET/CT with CT colonography (PET/CTC) improves the preoperative diagnosis of obstructive colorectal cancer (CRC).

METHODS

We prospectively included 47 consecutive patients (18 women and 29 men; mean age, 71 ± 14 years) suspected of having CRC by optical colonoscopy, which was not completed due to obstructive masses. To perform PET/CTC, a small caliber Foley catheter was inserted to distend the colon with CO2 insufflations. Polyps measuring 10 mm or larger were considered as high risk of malignancy. All findings were histologically confirmed.

RESULTS

Colorectal cancer was localized in the sigmoid (n = 21), rectum (n = 7), rectosigmoid junction (n = 5), ascending (n = 7), descending (n = 5), and transverse (n = 2) colon. All tumors showed FDG uptake (mean ± SD SUVmax, 20.02 ± 9.9) including one synchronic tumor (SUVmax, 10.46). Forty-seven polyps were histologically confirmed as smaller than 10 mm (n = 35) and 10 mm or larger (n = 12). All 12 polyps 10 mm or larger showed FDG uptake (SUVmax range, 3.08-19.5), but only one smaller than 10 mm could be identified by PET. Pathological lymph nodes were diagnosed in 17/47 cases after surgical removal with a sensitivity and specificity for CTC and PET/CTC of 71% and 97% and 59% and 100%, respectively. Liver metastases were confirmed in 9 patients and in 4/9 along with lung metastases (n = 2) or implants (n = 2), showing a sensitivity and specificity for CTC of 89% and 100% and both 100% for PET/CTC.

CONCLUSIONS

PET/CTC is a reliable technique for staging CRC and diagnosing synchronous tumors. In this series, PET/CTC was not able to identify small polyps but showed potential use for ruling out 10 mm or larger polyps at high risk of malignancy.

Colorectal cancer: Parametric evaluation of morphological, functional and molecular tomographic imaging

Colorectal cancer (CRC) represents one of the leading causes of tumor-related deaths worldwide. Among the various tools at physicians’ disposal for the diagnostic management of the disease, tomographic imaging (e.g., CT, MRI, and hybrid PET imaging) is considered essential. The qualitative and subjective evaluation of tomographic images is the main approach used to obtain valuable clinical information, although this strategy suffers from both intrinsic and operator-dependent limitations. More recently, advanced imaging techniques have been developed with the aim of overcoming these issues. Such techniques, such as diffusion-weighted MRI and perfusion imaging, were designed for the “in vivo” evaluation of specific biological tissue features in order to describe them in terms of quantitative parameters, which could answer questions difficult to address with conventional imaging alone (e.g., questions related to tissue characterization and prognosis). Furthermore, it has been observed that a large amount of numerical and statistical information is buried inside tomographic images, resulting in their invisibility during conventional assessment. This information can be extracted and represented in terms of quantitative parameters through different processes (e.g., texture analysis). Numerous researchers have focused their work on the significance of these quantitative imaging parameters for the management of CRC patients. In this review, we aimed to focus on evidence reported in the academic literature regarding the application of parametric imaging to the diagnosis, staging and prognosis of CRC while discussing future perspectives and present limitations. While the transition from purely anatomical to quantitative tomographic imaging appears achievable for CRC diagnostics, some essential milestones, such as scanning and analysis standardization and the definition of robust cut-off values, must be achieved before quantitative tomographic imaging can be incorporated into daily clinical practice.

Detection of incidental colorectal pathology on positron emission tomography/computed tomography

BACKGROUND

Positron emission tomography/computed tomography (PET/CT) is an important modality in cancer imaging. With its increasing availability and use, it is not uncommon to detect incidental focal colorectal ¹⁸ F-FDG uptake which poses a diagnostic challenge, as they may be associated with malignant or pre-malignant colorectal lesions. The aim of our study is to determine the proportion of these findings which represents true pathology.

METHODS

Patients with incidental focal colorectal ¹⁸ F-FDG uptake on PET/CT who subsequently underwent colonoscopy between January 2002 to September 2013 were identified from a prospective database in a tertiary referral centre. PET/CT results were correlated with colonoscopy and pathology results in these patients. Positive predictive values (PPVs) and 95% confidence intervals (CIs) of PET/CT in the detection of incidental colorectal pathology were calculated.

RESULTS

A total of 148 patients (92 men and 56 women), with a mean age 73 years (range of 36 to 93 years) were included in the study. A total of 170 foci of colorectal ¹⁸ F-FDG uptake were detected on PET/CT. Of these, 101 foci corresponded to a malignant or pre-malignant lesion (PPV 59%; 95% CI: 52-67%). On a per-patient analysis, 93 patients had at least one focus of colorectal ¹⁸ F-FDG uptake which corresponded to a pre-malignant or malignant lesion (PPV 63%; 95% CI: 54-71%).

CONCLUSION

Focal colorectal ¹⁸ F-FDG uptake on PET/CT is associated with a significant proportion of malignant or pre-malignant lesions. Further evaluation with colonoscopy is recommended.

Non-invasive diagnostic imaging of colorectal liver metastases

Colorectal cancer is one of the few malignant tumors in which synchronous or metachronous liver metastases [colorectal liver metastases (CRLMs)] may be treated with surgery. It has been demonstrated that resection of CRLMs improves the long-term prognosis. On the other hand, patients with un-resectable CRLMs may benefit from chemotherapy alone or in addition to liver-directed therapies. The choice of the most appropriate therapeutic management of CRLMs depends mostly on the diagnostic imaging. Nowadays, multiple non-invasive imaging modalities are available and those have a pivotal role in the workup of patients with CRLMs. Although extensive research has been performed with regards to the diagnostic performance of ultrasonography, computed tomography, positron emission tomography and magnetic resonance for the detection of CRLMs, the optimal imaging strategies for staging and follow up are still to be established. This largely due to the progressive technological and pharmacological advances which are constantly improving the accuracy of each imaging modality. This review describes the non-invasive imaging approaches of CRLMs reporting the technical features, the clinical indications, the advantages and the potential limitations of each modality, as well as including some information on the development of new imaging modalities, the role of new contrast media and the feasibility of using parametric image analysis as diagnostic marker of presence of CRLMs.

Virtual gastrointestinal colonoscopy in combination with large bowel endoscopy: Clinical application

Although colorectal cancer (CRC) has no longer been the leading cancer killer worldwide for years with the exponential development in computed tomography (CT) or magnetic resonance imaging, and positron emission tomography/CT as well as virtual colonoscopy for early detection, the CRC related mortality is still high. The objective of CRC screening is to reduce the burden of CRC and thereby the morbidity and mortality rates of the disease. It is believed that this goal can be achieved by regularly screening the average-risk population, enabling the detection of cancer at early, curable stages, and polyps before they become cancerous. Large-scale screening with multimodality imaging approaches plays an important role in reaching that goal to detect polyps, Crohn’s disease, ulcerative colitis and CRC in early stage. This article reviews kinds of presentative imaging procedures for various screening options and updates detecting, staging and re-staging of CRC patients for determining the optimal therapeutic method and forecasting the risk of CRC recurrence and the overall prognosis. The combination use of virtual colonoscopy and conventional endoscopy, advantages and limitations of these modalities are also discussed.

(18)F-FDG PET/CT findings of obstructive colitis proximal to colorectal cancer

PURPOSE

This study was performed to determine the frequency and patterns of obstructive colitis (OC) seen on F-FDG PET/CT scan of patients with adenocarcinoma of the colon and rectum.

PATIENTS AND METHODS

Preoperative PET/CT scans and surgical records of 308 patients with surgically proven colorectal adenocarcinoma were retrospectively reviewed for the presence of colon obstruction and OC proximal to the colorectal adenocarcinoma. The distributions, patterns, and SUVmax of OC were evaluated on PET/CT. Abdominal CT, colonoscopic finding, and histopathologic findings of surgical specimen were also reviewed.

RESULTS

Of 308 patients, PET/CT scans of 29 (9.4%) showed OC. The mean SUVmax of OC was 3.6 ± 2.2 (range, 1.6-12.3). Obstructive colitis was contiguous to the tumor in 23 patients (79.3%) and noncontiguous in 6 (20.7%). Obstructive colitis was diffuse in 25 patients (86%) and patchy in 4 (14%). It was segmental in 16 patients (55%) and pancolonic in 13 (45%). Twenty-three of 29 patients (79.3%) showed proximal wall thickening to colon cancer on abdominal CT performed about 3 days before PET/CT.The patients with OC on PET/CT was significantly associated with annular (P = 0.017), large-sized (P < 0.001), and advanced colon cancer (P < 0.001). However, there was no association between tumor size and SUVmax of OC.Ten proximal polyps were detected in 7 of 29 patients (24.1%) on colonoscopy and surgical specimen. Of these, 1 proximal polyp was removed before PET/CT scan, whereas the remaining 9 were not detected on PET/CT scan.

CONCLUSIONS

Obstructive colitis is predominantly diffuse and contiguous with the obstructing adenocarcinoma. Colorectal cancer with OC tends to show annular shape and larger tumor size. Obstructive colitis may lower the possibility of detection of synchronous proximal colonic lesion by PET/CT.

Management of patients following detection of unsuspected colon lesions by PET imaging

Positron emission tomography (PET) is a well-established and integral component of multimodality imaging in oncology. However, the expanded use of PET in oncological and also non-oncological imaging (such as in assessing inflammatory conditions) has identified more lesions or tumors at unsuspected locations, such as in the large bowel during examination of patients not known to have colorectal disease. We review the clinical significance of colon lesions that were discovered incidentally by PET imaging and management strategies for gastroenterologists.

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.

Positron emission tomography for benign and malignant disease

Functional imaging using radiolabeled probes that specifically bind and accumulate in target tissues has improved the sensitivity and specificity of conventional imaging. Fluorodeoxyglucose (FDG)-positron emission tomography (PET) has shown improved diagnostic accuracy in differentiating benign from malignant lesions in the setting of solitary pulmonary nodules. FDG-PET has become useful in preoperative staging of patients with lung cancer, and is being tested with many other malignancies for its ability to change patient management. This article provides an overview of the current status of FDG-PET and presents the challenges of moving toward routine use.

Nonlaxative PET/CT colonography: feasibility, acceptability, and pilot performance in patients at higher risk of colonic neoplasia

CT colonography without bowel preparation is a safer and better-tolerated alternative to full laxation protocols, but comparative sensitivity and specificity are potentially reduced. Uptake of (18)F-FDG by colonic neoplasia is well described, and combining PET with nonlaxative CT colonography could improve accuracy. The purpose was to prospectively test the technical feasibility and acceptability of combined nonlaxative PET/CT colonography in patients at higher risk of colorectal neoplasia and to provide pilot data on diagnostic performance.

METHODS

Fifty-six patients (median age, 64 y; 30 women) at high risk of colonic neoplasia underwent nonlaxative PET/CT colonography with barium fecal tagging within 2 wk of scheduled colonoscopy. Colonic segmental distension was graded 1 (poor) to 3 (good). A radiologist, experienced in CT colonography, and nuclear medicine physician in consensus analyzed the datasets. The diagnostic performance for standalone CT colonography and combined PET/CT colonography was compared with the reference colonoscopy. Patient experience for 25 items (each scored from 1 to 7) pertaining to satisfaction, worry, and physical discomfort was canvassed after both PET/CT colonography and colonoscopy.

RESULTS

Distension was good in 298 of 334 segments (89%; 95% confidence interval [CI], 85%-92%). Patients experienced more physical discomfort during colonoscopy (median, 4; interquartile range [IQR], 2-7) than during PET/CT colonography (median, 5; IQR, 3-7; P = 0.03) and were more willing to undergo PET/CT colonography again (36/43 [84%; 95% CI, 73%-95%] vs. 31/43 [72%; 95% CI, 59%-86%]; P = 0.001). Twenty-one patients had 54 polyps according to colonoscopy (10 with at least 1 polyp >or=6 mm and 8 with at least 1 polyp >or=10 mm). Of 14 polyps 6 mm or greater, 12 (86%; 95% CI, 67%-100%) were (18)F-FDG-avid, including all those 10 mm or greater (mean standardized uptake value, 10.1). CT colonography sensitivity for polyps 6 mm or larger was 92.9% (95% CI, 79.4%-100%) and was not improved by the addition of PET. However, combined PET/CT colonography review improved per-patient positive predictive value for a polyp 10 mm or greater from 73% (95% CI, 39-92) to 100% (95% CI, 60-100).

CONCLUSION

In this feasibility study, simultaneous PET acquisition during nonlaxative CT colonography is technically feasible, is well tolerated, and potentially improves specificity.

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.

Noninvasive radiologic imaging of the large intestine: a valuable complement to optical colonoscopy

PURPOSE OF REVIEW

Radiologic imaging of the large intestine continues to evolve and expand the potential for noninvasive diagnosis. The aim of this review is to provide an update on current and emerging clinical capabilities for a variety of radiologic diagnostic imaging tools for evaluating the colon and rectum.

RECENT FINDINGS

The utility of computed tomography for the evaluation of symptomatic inflammatory and neoplastic conditions of the colon is well established, but the clinical role of computed tomography colonography is rapidly evolving. In addition to a number of diagnostic indications, computed tomography colonography is emerging as a potential frontline colorectal screening test for cancer prevention. MRI has become increasingly valuable for rectal cancer staging and inflammatory bowel disease but has yet to gain momentum for polyp evaluation. PET imaging has been primarily utilized for oncologic indications, but also holds considerable potential for inflammatory conditions. Other imaging modalities, such as the barium enema, conventional radiography, and ultrasound, play a much more limited role.

SUMMARY

Advances in radiologic imaging of the colorectum will continue to expand the capabilities and clinical indications for noninvasive diagnosis, allowing for a greater emphasis on the complementary roles of tissue sampling and therapy with optical colonoscopy.

Functional imaging of colorectal cancer: positron emission tomography, magnetic resonance imaging, and computed tomography

In the past 10 years, overall survival and disease-free survival of patients with colorectal cancer (CRC) has improved substantially because of a combination of factors: (1) more accurate staging as a result of advances in imaging technology; (2) refinements in surgical technique; (3) 'curative' metastasectomy for patients with limited metastatic disease; (4) improvements in radiation therapy planning and greater precision of radiation therapy delivery; and (5) increasing chemotherapeutic options, including antiangiogenic and vascular targeting drugs. In this era of 'personalized medicine,' the increasingly individualized treatment of patients with CRC has highlighted the need for functional imaging techniques in addition to conventional anatomic-based imaging. This review discusses the contribution of positron emission tomography to the clinical management of CRC. In addition, evolving techniques such as dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), DCE computed tomography (perfusion CT), diffusion-weighted MRI, and blood oxygenation level-dependent MRI that might have a future role will be covered.

PET-CT in oncology: making the most of CT

Combined positron emission tomography–computed tomography (PET-CT) has made a significant impact on cancer imaging. The use of CT to map tissue attenuation for correction of PET images and the ability to co-register the functional information provided by PET with the anatomical data afforded by CT, has resulted in demonstrable improvements in diagnostic accuracy. However, attenuation correction and anatomical localisation may not represent the full benefits of integrating CT with PET. The use of CT acquisition techniques for patient positioning and the use of contrast media can improve diagnostic performance, and incorporation of CT image processing techniques such as perfusion CT, 3D imaging and computer-assisted diagnosis offers new applications. The interpretation of PET-CT images can be improved by fully integrating the morphological appearances on CT into image analysis. Better utilisation of the CT component of PET-CT could further enhance the benefits of PET-CT in oncology but will have implications for manufacturers and purchasers of PET-CT equipment and analysis software. Furthermore, specialists working in PET-CT will need CT competencies beyond knowledge of cross-sectional anatomy. CT continues to exhibit rapid evolution and these advances will inevitably impact on the practice of PET-CT.

Correction of oral contrast artifacts in CT-based attenuation correction of PET images using an automated segmentation algorithm

PURPOSE

Oral contrast is usually administered in most X-ray computed tomography (CT) examinations of the abdomen and the pelvis as it allows more accurate identification of the bowel and facilitates the interpretation of abdominal and pelvic CT studies. However, the misclassification of contrast medium with high-density bone in CT-based attenuation correction (CTAC) is known to generate artifacts in the attenuation map (mumap), thus resulting in overcorrection for attenuation of positron emission tomography (PET) images. In this study, we developed an automated algorithm for segmentation and classification of regions containing oral contrast medium to correct for artifacts in CT-attenuation-corrected PET images using the segmented contrast correction (SCC) algorithm.

METHODS

The proposed algorithm consists of two steps: first, high CT number object segmentation using combined region- and boundary-based segmentation and second, object classification to bone and contrast agent using a knowledge-based nonlinear fuzzy classifier. Thereafter, the CT numbers of pixels belonging to the region classified as contrast medium are substituted with their equivalent effective bone CT numbers using the SCC algorithm. The generated CT images are then down-sampled followed by Gaussian smoothing to match the resolution of PET images. A piecewise calibration curve was then used to convert CT pixel values to linear attenuation coefficients at 511 keV.

RESULTS

The visual assessment of segmented regions performed by an experienced radiologist confirmed the accuracy of the segmentation and classification algorithms for delineation of contrast-enhanced regions in clinical CT images. The quantitative analysis of generated mumaps of 21 clinical CT colonoscopy datasets showed an overestimation ranging between 24.4% and 37.3% in the 3D-classified regions depending on their volume and the concentration of contrast medium. Two PET/CT studies known to be problematic demonstrated the applicability of the technique in clinical setting. More importantly, correction of oral contrast artifacts improved the readability and interpretation of the PET scan and showed substantial decrease of the SUV (104.3%) after correction.

CONCLUSIONS

An automated segmentation algorithm for classification of irregular shapes of regions containing contrast medium was developed for wider applicability of the SCC algorithm for correction of oral contrast artifacts during the CTAC procedure. The algorithm is being refined and further validated in clinical setting.