Positive and negative contrast agents in CT evaluation of the abdomen and pelvis

Bowel Emergencies in Patients With Cancer

Cancer is the second most common cause of death worldwide. Bowel emergencies in patients with cancer are becoming increasingly more prevalent due to advances in cancer therapy and longer overall patient survival. When these patients present acutely, they are often frail and may have pre-existing co-morbidities. This article discusses the imaging features of bowel emergencies commonly encountered in oncological patients in clinical practice. These include chemotherapy related colitis, neutropenia enterocolitis and typhlitis, toxic megacolon, bowel perforation, malignant bowel obstruction and gastrointestinal haemorrhage. The radiologist plays a key role in identifying these oncological emergencies and guiding further management.

Optimizing Outpatient Oral Contrast Use in Abdominal CT-A Radiology Pandemic Response Initiative to Reduce Patient Time in the Waiting Room and Reduce Costs, While Improving Patient Experience

Purpose: The aim was to reduce outpatient wait time and improve patient experience by optimising oral contrast use. Methods: Our multidisciplinary stakeholder collaboration implemented two simultaneous interventions: (1) Creation of 'oral contrast policy', limiting recommended indications. (2) Creation of a new shorter oral contrast regime (30 vs 60 min). We conducted a retrospective service evaluation of oral contrast use in outpatient (OP) abdominal CT at baseline and post-intervention. Patient wait times were measured and per-patient cost-savings were reported. An image quality review was performed by 2 blinded abdominal radiologists. Patient experience was evaluated with a standard voluntary survey. Statistical analysis was performed comparing baseline and evaluation outcomes using Chi-square or Fisher Exact test for categorical variables and Student's t-test or ANOVA for continuous data. Results: Over 1-month periods, OP CT scans were assessed in baseline (pre-pandemic) n = 575, baseline (pandemic) n = 495 and post-intervention n = 545 groups. Oral contrast use reduced from 420/575, 73.0% at baseline to 178/545, 32.7% post intervention. The turn-around time reduced by 15.8 minutes per patient from 70.3 to 54.5 minutes, P < .001 (Interventions 1 and 2). The diagnostic quality did not differ between the oral contrast regimes (Intervention 2, P = 1.0, P = .08). No repeat CTs were needed due to lack of oral contrast (Intervention 1) or poor opacification (Intervention 2). There was oral contrast cost reductions of 69.1-78.4% (P < .001). Patients reported their overall experience was improved post-intervention (Interventions 1 and 2). Conclusions: Optimising the CT oral contrast service through judicious use and a shorter regime, reduced patient wait times, improved patient experience and preserved diagnostic quality.

Functional CT Contrast Nanoagents for the Tumor Microenvironment

Understanding the detailed tumor microenvironment (TME) is essential to achieve effective treatment of tumor, because TME has an extremely profound influence on the occurrence, development, invasion, and metastasis of tumor. It is of great significance to realize accurate diagnosis of the TME by using functional computed tomography (CT) contrast nanoagents (FCTNAs). Here, an overview of FCTNAs that respond to the overexpressed receptors, acidic microenvironment, overexpressed glutathione and enzymes, and hypoxia in tumor is provided, and also prospects the advance of novel spectral CT technique to detect the TME precisely. Utilizing FCTNAs is expected to achieve accurate monitoring of the TME and further provide guidance for the effective personalized tumor treatment in clinic.

Utility of CT oral contrast administration in the emergency department of a quaternary oncology hospital: diagnostic implications, turnaround times, and assessment of ED physician ordering

PURPOSE

To compare studies with and without oral contrast on performance of multidetector computed tomography (CT) and the order to CT examination turnaround time in cancer patients presenting to the emergency department (ED). To the best of our knowledge, oral contrast utility has not previously been specifically assessed in cancer patients presenting to the emergency department.

MATERIALS & METHODS

Retrospective review of CT abdomen examinations performed in oncology patients presenting to the emergency department during one month. CT examinations performed with and without oral contrast were rated by two consensus readers for degree of confidence and diagnostic ability. Correlations were assessed for primary cancer type, age, sex, chief complaint/examination indication, body mass index, intravenous contrast status, repeat CT examination within 4 weeks, and disposition. Turnaround times from order to the start of the CT examination were calculated.

RESULTS

The studied group consisted of 267 patients (127 men and 140 women) with a mean age of 56 years and a mean body mass index of 27.8 kg/m². One hundred sixty CT examinations were performed without oral contrast, and 107 CT examinations were performed with oral contrast. There was no significant difference between cases with oral contrast and cases without oral contrast in the number of cases rated as "improved confidence" (odds ratio [OR] 0.54, 95% confidence interval [CI] 0.23-1.31, P = 0.17), "improved diagnosis" (OR 0.58, 95% CI 0.20-1.64, P = 0.3), "impaired confidence" (OR 3.92, 95% CI 0.46-33.06, P = 0.21), or "impaired diagnosis" (OR 2.63, 95% CI 0.29-23.89, P = 0.39). The turnaround time in the group receiving oral contrast (mean, 141 min; standard deviation, 49.8 min) was significantly longer than that in the group not receiving oral contrast (mean, 109.2 min; standard deviation, 64.8 min) with a mean difference of 31.8 min (P < 0.0001).

CONCLUSION

On the basis of our findings and prior studies, targeted rather than default use of oral contrast shows acceptable diagnostic ability in the emergency setting for oncology patients. Benefit from oral contrast use is suggested in scenarios such as suspected fistula/bowel leak/abscess, hypoattenuating peritoneal disease, prior bowel surgery such as gastric bypass, and the absence of intravenous contrast administration. Improvement through the use of targeted oral contrast administration also supports the emergency department need for prompt diagnosis and disposition.

Impact of low-energy CT imaging on selection of positive oral contrast media concentration

OBJECTIVES

To determine to what extent low-energy CT imaging affects attenuation of gastrointestinal tract (GIT) opacified with positive oral contrast media (OCM). Second, to establish optimal OCM concentrations for low-energy diagnostic CT exams.

METHODS

One hundred patients (38 men and 62 women; age 62 ± 11 years; BMI 26 ± 5) with positive OCM-enhanced 120-kVp single-energy CT (SECT), and follow-up 100-kVp acquisitions (group A; n = 50), or 40-70-keV reconstructions from rapid kV switching-single-source dual-energy CT (ssDECT) (group B; n = 50) were included. Luminal attenuation from different GIT segments was compared between exams. Standard dose of three OCM and diluted solutions (75%, 50%, and 25% concentrations) were introduced serially in a gastrointestinal phantom and scanned using SECT (120, 100, and 80 kVp) and DECT (80/140 kVp) acquisitions on a ssDECT scanner. Luminal attenuation was obtained on SECT and DECT images (40-70 keV), and compared to 120-kVp scans with standard OCM concentrations.

RESULTS

Luminal attenuation was higher on 100-kVp (328 HU) and on 40-60-keV images (410-924 HU) in comparison to 120-kVp scans (298 HU) in groups A and B (p < 0.05). Phantom: There was an inverse correlation between luminal attenuation and X-ray energy, increasing up to 527 HU on low-kVp and 999 HU on low-keV images (p < 0.05). 25% and 50% diluted OCM solutions provided similar or higher attenuation than 120 kVp, at low kVp and keV, respectively.

CONCLUSIONS

Low-energy CT imaging increases the attenuation of GIT opacified with positive OCM, permitting reduction of 25%-75% OCM concentration.

Use of positive oral contrast agents in abdominopelvic computed tomography for blunt abdominal injury: meta-analysis and systematic review

OBJECTIVES

To determine whether positive oral contrast agents improve accuracy of abdominopelvic CT compared with no, neutral or negative oral contrast agent.

METHODS

Literature was searched for studies evaluating the diagnostic performance of abdominopelvic CT with positive oral contrast agents against imaging with no, neutral or negative oral contrast agent. Meta-analysis reviewed studies correlating CT findings of blunt abdominal injury with positive and without oral contrast agents against surgical, autopsy or clinical outcome allowing derivation of pooled sensitivity and specificity. Systematic review was performed on studies with common design and reference standard.

RESULTS

Thirty-two studies were divided into two groups. Group 1 comprised 15 studies comparing CT with positive and without oral contrast agents. Meta-analysis of five studies from group 1 provided no difference in sensitivity or specificity between CT with positive or without oral contrast agents. Group 2 comprised 17 studies comparing CT with positive and neutral or negative oral contrast agents. Systematic review of 12 studies from group 2 indicated that neutral or negative oral contrasts were as effective as positive oral contrast agents for bowel visualisation.

CONCLUSIONS

There is no difference in accuracy between CT performed with positive oral contrast agents or with no, neutral or negative oral contrast agent.

KEY POINTS

• There is no difference in the accuracy of CT with or without oral contrast agent. • There is no difference in the accuracy of CT with Gastrografin or water. • Omission of oral contrast, utilising neutral or negative oral contrast agent saves time, costs and decreases risk of aspiration.

Routine use of positive oral contrast material is not required for oncology patients undergoing follow-up multidetector CT

The purpose of this retrospective medical audit was to evaluate the effect of discontinuing routine administration of oral contrast material to oncology patients undergoing follow-up multidetector computed tomography (CT) on reader evaluation of study adequacy. Analysis of 100 patients' experience of CT shows that positive oral contrast material was their least pleasant experience (P < .0001). Abandoning the routine use of positive oral contrast material for follow-up scans in general oncology patients undergoing multidetector CT, with section reconstruction thickness of 2.5 mm, was audited for 447 patents and included 5-13-month follow-up. The patient satisfaction study and clinical audit were performed according to local institutional audit guidelines. Since this was a clinical audit project, ethical approval was not required under UK National Health Service research governance arrangements. No patient needed to be recalled, no related diagnostic error has been reported, and follow-up CT, available in 285 of 447 cases (64%), revealed no error on the audited scan. We conclude that the routine use of positive oral contrast material is unnecessary for follow-up multidetector CT for general oncology indications.

Patient encounter time intervals in the evaluation of emergency department patients requiring abdominopelvic CT: oral contrast versus no contrast

The aim of the study was to assess various time intervals during patient encounters involving unenhanced (NECT) versus oral-contrast-enhanced (CECT) abdominopelvic (A/P) CT performed in the emergency department (ED) on adult patients presenting with acute abdominal pain. Computerized patient order entry and administrative data as well as scans themselves were retrospectively evaluated at a high-volume (107,000 visits per annum) regional medical center urban ED for a period of 30 consecutive days. All adult patients who had CT of abdomen and pelvis for abdominal pain during the 30 days of the study period were included. Data collected included demographic information, time of registration, time of first encounter in the ED, time of CT order, clinical indication for scan, time of scan, time of disposition (i.e., discharge or admit), and final disposition. Patients were excluded if they were less than 16 years old, pregnant, or met criteria for major trauma and evaluation in the trauma suite. Patients were also excluded from analysis if they received more than one scan on the same day (3 patients). Of 183 patients, 102 underwent NECT and 81 CECT. Some of the patients who underwent NECT had urinary colic. Among patients who did not have urinary colic there is a statistically significant difference in the median time intervals between: (1) patient arrival in the ED and evaluation by a physician (NECT 57 min, CECT 84 min, P<0.001); (2) patient exam by the physician and the time the A/P CT was ordered (NECT 35 min, CECT 63 min, P<0.01); (3) receipt of the CT order and the time of the scan (NECT 104 min, CECT 172 min, P<0.001); and (4) time of arrival in ED and disposition (NECT 358 min, CECT 599 min, P<0.001). There are significant time interval differences between CECT and NECT during patient encounters involving adults presenting with abdominal pain to the ED. The differences are greater than the amount of time allotted for opacification of small bowel (90 min). Baseline data such as these may prove useful in assessing the efficacy of scan techniques and improving resource utilization.

Application of oral contrast media in coregistered positron emission tomography-CT

OBJECTIVE

Coregistration of positron emission tomography (PET) and CT images results in significantly improved localization of abnormal FDG uptake compared with PET images alone. For delineation of intestinal structures, application of oral contrast media is a standard procedure in CT. The influence of oral contrast agents in PET imaging using CT data for attenuation correction was evaluated in a comparative study on an in-line PET-CT system.

SUBJECTS AND METHODS

Sixty patients referred for PET-CT were evaluated in two groups. One group of 30 patients received oral Gastrografin 45 min before data acquisition. The second group received no contrast medium. PET images were reconstructed, using CT data for attenuation correction. Image analysis was performed by two reviewers in consensus, using a 4-point scale comparing FDG-uptake in the gastrointestinal tract in PET images of both groups. Furthermore, correlation of FDG uptake and localization of contrast media in the intestinal tract in CT images were determined.

RESULTS

No significant difference in FDG uptake in PET images in all regions of the gastrointestinal tract except the ascending colon was seen in both groups. No correlation was found in the location of increased FDG uptake and contrast media in the CT images.

CONCLUSION

An oral contrast agent can be used for coregistered PET-CT without the introduction of artifacts in PET.

Evaluation of an experimental low-attenuation gastrointestinal contrast agent for CT imaging of intestinal ischemia in an animal model

RATIONALE AND OBJECTIVES

The authors evaluated the use of MRX-320, a low-attenuation, expansile oral contrast agent, for the demonstration of intestinal ischemia in an animal model.

MATERIALS AND METHODS

Nine dogs were given either MRX-320, water, or diatrizoate as an oral contrast agent through a jejunostomy tube. Two dogs received no oral contrast agent. Helical computed tomography (CT) was performed before the intravenous injection of 2.5 mL/kg iohexol at 4 mL/sec, during the arterial phase, and during the portal venous phase. Mesenteric ischemia was surgically induced, and the imaging protocol was repeated. Three readers rated the randomly assigned images for quality and demonstration of ischemia. Attenuation values for the intestinal lumen and wall were recorded.

RESULTS

Examinations performed with MRX-320 provided the best discrimination between ischemic and nonischemic conditions (P < .05), followed by examinations with no oral contrast medium, examinations with water, and examinations with diatrizoate. Images obtained with MRX-320 also scored significantly higher on measures of image quality than those obtained with water or no oral contrast medium (P < .05). On images obtained with MRX-320, the bowel lumen measured -836.5 HU (P < .05 compared with other techniques). Water provided the least uniformity of distention, and diatrizoate provided the least mucosal detail.

CONCLUSION

The use of MRX-320 as an oral contrast agent with an intravenous bolus of iohexol at CT increased reader confidence for the diagnosis of intestinal ischemia and improved subjective measures of image quality.