The effect of oral contrast on large bowel activity in FDG-PET/CT

Comprehensive literature review of oral and intravenous contrast-enhanced PET/CT: a step forward?

The integration of diagnostic CT scans into PET/CT facilitates a comprehensive single examination, presenting potential advantages for patients seeking a thorough one-shot check-up. The introduction of iodinated contrast media during PET scanning raises theoretical concerns about potential interference with uptake quantification, due to the modification of tissue density on CT. Nevertheless, this impact appears generally insignificant for clinical use, compared to the intrinsic variability of standardized uptake values. On the other hand, with the growing indications of PET, especially 18F-FDG PET, contrast enhancement increases the diagnostic performances of the exam, and provides additional information. This improvement in performance achieved through contrast-enhanced PET/CT must be carefully evaluated considering the associated risks and side-effects stemming from the administration of iodinated contrast media. Within this article, we present a comprehensive literature review of contrast enhanced PET/CT, examining the potential impact of iodinated contrast media on quantification, additional side-effects and the pivotal clinically demonstrated benefits of an all-encompassing examination for patients. In conclusion, the clinical benefits of iodinated contrast media are mainly validated by the large diffusion in PET protocols. Contrary to positive oral contrast, which does not appear to offer any major advantage in patient management, intravenous iodine contrast media provides clinical benefits without significant artifact on images or quantification. However, studies on the benefit-risk balance for patients are still lacking.

The effect of butylscopolamine on [18F]FDG uptake in the gastrointestinal tract is negligible and regionally variable

BACKGROUND

Butylscopolamine (or hyoscine butylbromide, trade name Buscopan^®) is occasionally administered as a premedication to reduce non-specific FDG uptake in the gastrointestinal tract based on its antiperistaltic effect. To date, there are no consistent recommendations for its use. The aim of this study was to quantify the reduction in intestinal and non-intestinal uptake by butylscopolamine administration and to derive relevance for clinical evaluation.

RESULTS

458 patients (PET/CT for lung cancer) were retrospectively reviewed. 218 patients with butylscopolamine and 240 patients without butylscopolamine had comparable characteristics. While the SUV_mean in the gullet/stomach and small intestine was significantly reduced with butylscopolamine, the colon and rectum/anus showed no difference. The liver and salivary glands showed a reduced SUV_mean, while skeletal muscle and blood pool were unaffected. An effect of butylscopolamine was particularly evident in men and patients under 65 years of age. There was no difference in the perceived confidence in the assessment of intestinal findings in the subjective evaluation, although in the butylscopolamine group further diagnostics appeared advisable more frequently.

CONCLUSIONS

Butylscopolamine reduces gastrointestinal FDG accumulation only in selected segments and, despite a significant effect, only to a small extent. A general recommendation for the use of butylscopolamine cannot be derived from these results, its use for specific issues could be considered individually.

Optimized 18F-FDG PET-CT Method to Improve Accuracy of Diagnosis of Metastatic Cancer

The diagnosis of cancer by FDG PET-CT is often inaccurate owing to subjectivity of interpretation. We compared the accuracy of a novel normalized (standardized) method of interpretation with conventional non-normalized SUV. Patients (n = 393) with various malignancies were studied with FDG PET/CT to determine the presence or absence of cancer. Target lesions were assessed by two methods: (1) conventional SUV_max (conSUV_max) and (2) a novel method that combined multiple factors to optimize SUV (optSUVmax), including the patient's normal liver SUV_max, a liver constant (k) derived from a review of the literature, and use of site-specific thresholds for malignancy. The two methods were compared to pathology findings in 154 patients being evaluated for mediastinal and/or hilar lymph node (MHLNs) metastases, 143 evaluated for extra-thoracic lymph node (ETLNs) metastases, and 96 evaluated for liver metastases. OptSUV_max was superior to conSUV_max for all patient groups. For MHLNs, sensitivity was 83.8% vs. 80.7% and specificity 88.7% vs. 9.6%, respectively; for ETLNs, sensitivity was 92.1% vs. 77.8% and specificity 80.1% vs. 27.6%, respectively; and for lesions in the liver parenchyma, sensitivity was 96.1% vs. 82.3% and specificity 88.8% vs. 23.0%, respectively. Optimized SUV_max increased diagnostic accuracy of FDG PET-CT for cancer when compared with conventional SUV_max interpretation.

The role of PET imaging in inflammatory bowel diseases: state-of-the-art review

Inflammatory bowel diseases (IBD), i.e. Crohn disease and ulcerative colitis, are autoimmune processes of undetermined origin characterized by the chronic inflammation of the digestive tract. There is no single gold-standard to diagnose IBD which is therefore carried out through the combination of endoscopy, biopsy, radiological and biological investigations; and the development of non-invasive technique allowing the assessment and monitoring of these diseases is necessary. In this state-of-the-art review of the literature, we present the results of PET imaging studies for the diagnosis and staging of IBD (suspected or known), response evaluation to treatment and evaluation of one the main complication, i.e. strictures; explain the reasons why this examination is currently not considered in the IBD guidelines, e.g. radiation exposure, lack of standardization and not validated performances; and finally discuss the perspectives that could possibly allow it to find a place in the future, e.g. digital PET-CT, dynamic PET images acquisition, new radiopharmaceuticals, use of radiomics and use of artificial intelligence for automatically characterize and quantify digestive [¹⁸F]FDG uptake.

Evaluation of dual time-point fluorodeoxyglucose PET/computed tomography imaging in gastric cancer

BACKGROUND

We aimed to evaluate the efficiency of dual time-point fluorodeoxyglucose (FDG) PET/computed tomography (CT) imaging in detecting primary and metastatic lesions in gastric cancer.

METHODS

Between May 2019 and January 2020, 52 patients with gastric carcinoma were prospectively involved in our study. And dual time-point FDG PET/CT imaging performed to the patients. Of detected primary and metastatic lesions, the ones that are better visualized or only appear in delayed imaging were visually identified. Also, maximum standardized uptake value (SUVmax) of the primary and metastatic lesions and the intact liver tissue were measured in early and delayed imaging. Acquired SUVmax values and SUVmax ratios were compared statistically.

RESULTS

In delayed images, lesions were better visualized in 32 patients (61.5%) and extra lesions were detected in 4 patients (7.7%). SUVmax of primary tumor, SUVmax of liver metastases, SUVmax of lymph node metastases, primary tumor SUVmax/liver SUVmax ratio and lymph node metastasis SUVmax/liver SUVmax ratio were significantly higher in delayed images (P < 0.001, P = 0.022, P < 0.001, P < 0.001, P < 0.001, respectively). However, SUVmax of liver parenchyma was significantly lower in delayed images (P < 0.001).

CONCLUSIONS

There is a visually and statistically significant increase in the number and detectability of lesions seen in delayed images and dual time-point FDG PET/CT imaging seems useful in detecting primary and metastatic lesions in gastric cancer.

Diffuse Intense Intestinal FDG Activity in a Patient With Familial Adenomatous Polyposis

Familial adenomatous polyposis is a rare autosomal dominant intestinal syndrome with a high rate of malignant transformation. Here, we report a 20-year-old woman with a diagnosis of familial adenomatous polyposis by pathologic examination after colonoscopy biopsy, who underwent an F-FDG PET/CT to assess the extent of this disease. The images showed diffuse elevated FDG uptake along the entire colorectum. Additionally, focal enlarged lymph nodes with increased FDG uptake were noted. These findings promoted proctocolectomy and lymphadenectomy.

Quantification of 18FDG in the Normal Colon-A First Step in Investigating Whether Its Presence Is a Marker of a Physiological Process

The visibility of the colon in positron emission tomography (PET) scans of patients without gastrointestinal disease indicating the presence of ¹⁸F Fluorodeoxyglucose (¹⁸FDG) is well recognised, but unquantified and unexplained. In this paper a qualitative scoring system was applied to PET scans from 30 randomly selected patients without gastrointestinal disease to detect the presence of ¹⁸FDG in 4 different sections of the colon and then both the total pixel value and the pixel value per unit length of each section of the colon were determined to quantify the amount of ¹⁸FDG from a randomly selected subset of 10 of these patients. Analysis of the qualitative scores using a non-parametric ANOVA showed that all sections of the colon contained ¹⁸FDG but there were differences in the amount of ¹⁸FDG present between sections (p<0.05). Wilcoxon matched-pair signed-rank tests between pairs of segments showed statistically significant differences between all pairs (p<0.05) with the exception of the caecum and ascending colon and the descending colon. The same non-parametric statistical analysis of the quantitative measures showed no difference in the total amount of ¹⁸FDG between sections (p>0.05), but a difference in the amount/unit length between sections (p<0.01) with only the caecum and ascending colon and the descending colon having a statistically significant difference (p<0.05). These results are consistent since the eye is drawn to focal localisation of the ¹⁸FDG when qualitatively scoring the scans. The presence of ¹⁸FDG in the colon is counterintuitive since it must be passing from the blood to the lumen through the colonic wall. There is no active mechanism to achieve this and therefore we hypothesise that the transport is a passive process driven by the concentration gradient of ¹⁸FDG across the colonic wall. This hypothesis is consistent with the results obtained from the qualitative and quantitative measures analysed.

FDG PET/CT: EANM procedure guidelines for tumour imaging: version 2.0

The purpose of these guidelines is to assist physicians in recommending, performing, interpreting and reporting the results of FDG PET/CT for oncological imaging of adult patients. PET is a quantitative imaging technique and therefore requires a common quality control (QC)/quality assurance (QA) procedure to maintain the accuracy and precision of quantitation. Repeatability and reproducibility are two essential requirements for any quantitative measurement and/or imaging biomarker. Repeatability relates to the uncertainty in obtaining the same result in the same patient when he or she is examined more than once on the same system. However, imaging biomarkers should also have adequate reproducibility, i.e. the ability to yield the same result in the same patient when that patient is examined on different systems and at different imaging sites. Adequate repeatability and reproducibility are essential for the clinical management of patients and the use of FDG PET/CT within multicentre trials. A common standardised imaging procedure will help promote the appropriate use of FDG PET/CT imaging and increase the value of publications and, therefore, their contribution to evidence-based medicine. Moreover, consistency in numerical values between platforms and institutes that acquire the data will potentially enhance the role of semiquantitative and quantitative image interpretation. Precision and accuracy are additionally important as FDG PET/CT is used to evaluate tumour response as well as for diagnosis, prognosis and staging. Therefore both the previous and these new guidelines specifically aim to achieve standardised uptake value harmonisation in multicentre settings.

Utility of positron emission tomography/CT in the evaluation of small bowel pathology

We describe the management principles and different roles of positron emission tomography (PET)/CT in the evaluation of patients with small bowel tumours (adenocarcinoma, gastrointestinal stromal tumour, lymphoma, metastases) from initial staging, monitoring response to treatment, to detection of recurrent disease. We also discuss the various non-malignant aetiologies of small bowel fludeoxyglucose (FDG) PET uptake, and other pitfalls in FDG PET/CT interpretation. Awareness of the imaging appearances of small bowel tumours, patterns of disease spread and potential PET/CT interpretation pitfalls are of paramount importance to optimise diagnostic accuracy.

Quantitative analysis shows that contrast medium in positron emission tomography/computed tomography may cause significant artefacts

OBJECTIVES

Attenuation correction algorithms are required for accurate quantification of PET data and for mapping of radioactive tracers. Modern PET systems incorporate computed tomography (CT) systems to perform attenuation correction. However, high-density media, such as contrast agents, may introduce potentially clinically significant artefacts in PET images when CT-based attenuation correction algorithms are used. Although various groups have investigated this issue, no study has quantitatively assessed the clinical significance of these artefacts by comparing artefact and lesion standardized uptake values (SUVs) in controlled phantom experiments. Furthermore, previous studies have focussed on the effects of increasing the concentration of contrast medium, without investigating the effects of increasing its transaxial area. This study quantifies the clinical significance of increasing the concentration and transaxial area of contrast agents and evaluates a commercially available contrast agent correction algorithm.

METHODS

Images of a phantom containing background activity, a volume of contrast agent and varying sizes of hot lesions were acquired using clinical acquisition protocols. Quantitative analysis was performed on transaxial image slices of PET data.

RESULTS

The densest medium caused a 125% SUV(mean) increase in the area containing, and immediately adjacent to, contrast medium when compared with a reference water phantom. As the transaxial area of the contrast medium increased, artefacts appeared as a ring of activity around the periphery of the contrast medium. The contrast correction algorithm reduced these artefacts to within ± 39% of the reference results.

CONCLUSION

Oral and IV contrast agents can cause clinically significant artefacts in CT-based attenuation-corrected PET images and should be used with caution.

Spectrum of 18F-FDG PET/CT findings in patients presenting with fever of unknown origin

OBJECTIVE

The objective of this article is to provide an illustrative tutorial highlighting the clinical utility of (18)F-FDG PET/CT for imaging patients presenting with fever of unknown origin (FUO).

CONCLUSION

FDG PET/CT is a powerful tool in localizing an inciting source in patients with FUO. The high sensitivity of FDG PET/CT for diagnosing infective, inflammatory, and neoplastic processes can be exploited in this setting because these processes are often the common causes of FUO.

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 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/computed tomography

Accurate anatomical localization of functional abnormalities obtained with the use of positron emission tomography (PET) is known to be problematic. Although tracers such as (18)F-fluorodeoxyglucose ((18)F-FDG) visualize certain normal anatomical structures, the spatial resolution is generally inadequate for accurate anatomic localization of pathology. Combining PET with a high-resolution anatomical imaging modality such as computed tomography (CT) can resolve the localization issue as long as the images from the two modalities are accurately coregistered. However, software-based registration techniques have difficulty accounting for differences in patient positioning and involuntary movement of internal organs, often necessitating labor-intensive nonlinear mapping that may not converge to a satisfactory result. Acquiring both CT and PET images in the same scanner obviates the need for software registration and routinely provides accurately aligned images of anatomy and function in a single scan. A CT scanner positioned in line with a PET scanner and with a common patient couch and operating console has provided a practical solution to anatomical and functional image registration. Axial translation of the couch between the 2 modalities enables both CT and PET data to be acquired during a single imaging session. In addition, the CT images can be used to generate essentially noiseless attenuation correction factors for the PET emission data. By minimizing patient movement between the CT and PET scans and accounting for the axial separation of the two modalities, accurately registered anatomical and functional images can be obtained. Since the introduction of the first PET/CT prototype more than 6 years ago, numerous patients with cancer have been scanned on commercial PET/CT devices worldwide. The commercial designs feature multidetector spiral CT and high-performance PET components. Experience has demonstrated an increased level of accuracy and confidence in the interpretation of the combined study as compared with studies acquired separately, particularly in distinguishing pathology from normal, physiologic tracer uptake and precisely localizing abnormal foci. Combined PET/CT scanners represent an important evolution in technology that has helped to bring molecular imaging to the forefront in cancer diagnosis, staging and therapy monitoring.

Advances in Attenuation Correction Techniques in PET

Molecular imaging using PET has evolved from a vigorous academic field into the clinical arena. Considerable advances have been made in the design of high-resolution standalone PET and combined PET/CT units dedicated to clinical whole-body scanning. Likewise, much worthwhile research focused on the development of quantitative imaging protocols incorporating accurate data correction techniques and sophisticated image reconstruction algorithms. Since its inception, photon attenuation in biological tissues has been identified as the most important physical degrading factor affecting PET image quality and quantitative accuracy. Various strategies have been devised to determine an accurate attenuation map to enable correction for nonlinear photon attenuation in whole-body PET studies. This article presents the physical and methodological basis of photon attenuation and summarizes state-of-the-art developments in algorithms used to derive the attenuation map aiming at accurate attenuation compensation of PET data. Future prospects, research trends, and challenges are identified, and directions for future research are discussed.

Attenuation-corrected vs. nonattenuation-corrected 2-deoxy-2-[F-18]fluoro-D-glucose-positron emission tomography in oncology: a systematic review

Purpose

To perform a systematic review and meta-analysis to determine the diagnostic accuracy of attenuation-corrected (AC) vs. nonattenuation-corrected (NAC) 2-deoxy-2-[F-18]fluoro-d-glucose-positron emission tomography (FDG-PET) in oncological patients.

Procedures

Following a comprehensive search of the literature, two reviewers independently assessed the methodological quality of eligible studies. The diagnostic value of AC was studied through its sensitivity/specificity compared to histology, and by comparing the relative lesion detection rate reported with NAC-PET vs. AC, for full-ring and dual-head coincidence PET (FR- and DH-PET, respectively).

Results

Twelve studies were included. For FR-PET, the pooled sensitivity/specificity on a patient basis was 64/97% for AC and 62/99% for NAC, respectively. Pooled lesion detection with NAC vs. AC was 98% [95% confidence interval (95% CI): 96–99%, n = 1,012 lesions] for FR-PET, and 88% (95% CI:81–94%, n = 288 lesions) for DH-PET.

Conclusions

Findings suggest similar sensitivity/specificity and lesion detection for NAC vs. AC FR-PET and significantly higher lesion detection for NAC vs. AC DH-PET.

High-density materials do not always induce artifacts on PET/CT: What is responsible for the difference?

OBJECTIVE

PET/CT often show increased uptake at sites of high-density materials. However, some materials seldom demonstrate increased uptake on PET/CT, such as the materials used in hip prostheses. We hypothesized that the motion of materials may be crucial for such artifacts. Here, we present representative cases, and validate our hypothesis based on the results of phantom studies.

METHODS

A standard cylinder, 20 cm in diameter, was filled with approximately 37 MBq of 18F-based activity, and a pacemaker was attached to the side of the cylinder. This phantom was placed on the bed with the pacemaker side facing the scanner. PET scans were performed using a Biograph LSO DUO. CT scans were performed first for transmission scans, followed by acquisition of emission scans. The phantom was first scanned (protocol 1). The phantom was then moved about 2 cm closer to the distal edge of the bed just after transmission CT scan, and the emission scan was performed (protocol 2).

RESULTS

Homogenous uptake was seen in the cylinder in protocol 1, and there was no visible uptake at the site of the pacemaker. In contrast, a clear hotspot was seen at the site of the pacemaker in protocol 2. The uptake in the cylinder was inhomogeneous; that on the pacemaker side of the cylinder was low, while that on the opposite side was high.

CONCLUSIONS

High-density materials do not show false increased uptake without motion on PET/CT. Motion of these materials surrounded by radioactive organs may play an important role in inducing false increased uptake on PET/CT.

Bowel hot spots at PET-CT

Positron emission tomography (PET) with 2-[fluorine-18]fluoro-2-deoxy-d-glucose (FDG) has been shown to be sensitive in the detection of many bowel malignancies, but its specificity is lower because of various physiologic and pathologic patterns of bowel FDG uptake. PET-computed tomography (CT) can be useful in localizing and characterizing foci of increased FDG uptake within the bowel. As the use of PET-CT in the staging and monitoring of oncologic disease continues to expand, familiarity with these patterns of bowel FDG uptake is essential and can help determine the need for and the relative urgency of further testing. Although a variety of imaging protocols are used for PET-CT, the use of negative oral contrast agent allows improved bowel distention while eliminating potential artifacts caused by high-density oral contrast agents. In addition, correlation with the CT portion of the combined PET-CT examination can sometimes help identify the cause of focal or segmental bowel uptake. The radiologist should be aware of potential pitfalls in the evaluation of FDG-avid foci within the abdomen, including bowel motility and low-attenuation lesions mimicking bowel. Nevertheless, even though the precise role of combined PET-CT for bowel assessment has yet to be determined, the application of sound basic principles of image interpretation will help ensure the accurate interpretation of bowel findings seen with this combined modality.

Multimodality in vivo imaging systems: twice the power or double the trouble?

Many different types of radiation have been exploited to provide images of the structure and function of tissues inside a living subject. Each imaging modality is characterized by differing resolutions on the spatial and temporal scales, and by a different sensitivity for measuring properties related to morphology or function. Combinations of imaging modalities that integrate the strengths of two modalities, and at the same time eliminate one or more weaknesses of an individual modality, thus offer the prospect of improved diagnostics, therapeutic monitoring, and preclinical research using imaging approaches. This review discusses the advantages and challenges in developing multimodality imaging systems for in vivo use, highlights some successful combinations that are now routinely used in the clinic and in research, and discusses recent advances in multimodality instrumentation that may offer new opportunities for imaging.