Gastrointestinal Bleeding Scintigraphy in the Early 21st Century

SPECT/CT in the Diagnosis of Ectopic Gastric Mucosa-Meckel's Diverticulum

Aim  The imaging of Meckel's diverticulum (MD) is based of accumulation of Tc-99m pertechnetate in the ectopic gastric mucosa (EGM) content. Although the diagnostic accuracy of this imaging modality is high, there are some overlap patients with coexisting gastrointestinal bleeding and false positive causes hampering diagnostic power. The aim of this study was to evaluate the possible contribution of single-photon emission computed tomography/computed tomography (SPECT/CT) in EGM-MD diagnosis and to determine the indication of this additional imaging modality. Materials and Methods  Fifty-two pediatric patients (24 girls, 28 boys; mean age: 8.06 ± 5.22 years old) who have suspicion of MD and referred for scintigraphy were evaluated retrospectively. Additional SPECT/CT were performed to selected five cases among the group. The results of the scintigraphy as well as SPECT/CT were compared with endoscopy, pathology, and/or follow-up results. Results  There were 9 patients with equivocal study results, 12 positive results, and the others were considered negative MD scintigraphy. One patient was out of follow-up and 10 patients underwent surgery. Only one single patient was negative during surgery but scintigraphy was also negative. The diagnostic sensitivity, specificity, and accuracy were 100, 95, and 96%, respectively. Among five patients with SPECT/CT results one patient was diagnosed by only SPECT/CT who had EGM in duplication cyst, one equivocal patient was diagnosed as descending colon bleeding, and one patient's lesion was clearly delineated by SPECT/CT. Conclusion  SPECT/CT has clear advantage over standard planar scintigraphy imaging in EGM-MD determination. This modality might decrease equivocal and false positive results but this issue has to be addressed with further studies.

Protein click chemistry and its potential for medical applications

A revolution in chemical biology occurred with the introduction of click chemistry. Click chemistry plays an important role in protein chemistry modifications, providing specific, sensitive, rapid, and easy-to-handle methods. Under physiological conditions, click chemistry often overlaps with bioorthogonal chemistry, defined as reactions that occur rapidly and selectively without interfering with biological processes. Click chemistry is used for the posttranslational modification of proteins based on covalent bond formations. With the contribution of click reactions, selective modification of proteins would be developed, representing an alternative to other technologies in preparing new proteins or enzymes for studying specific protein functions in different biological processes. Click-modified proteins have potential in diverse applications such as imaging, labeling, sensing, drug design, and enzyme technology. Due to the promising role of proteins in disease diagnosis and therapy, this review aims to highlight the growing applications of click strategies in protein chemistry over the last two decades, with a special emphasis on medicinal applications.

The Role of Imaging for GI Bleeding: ACG and SAR Consensus Recommendations

Gastrointestinal (GI) bleeding is the most common GI diagnosis leading to hospitalization within the United States. Prompt diagnosis and treatment of GI bleeding is critical to improving patient outcomes and reducing high health care utilization and costs. Radiologic techniques including CT angiography, catheter angiography, CT enterography, MR enterography, nuclear medicine red blood cell scan, and technetium-99m pertechnetate scintigraphy (Meckel scan) are frequently used to evaluate patients with GI bleeding and are complementary to GI endoscopy. However, multiple management guidelines exist, which differ in the recommended utilization of these radiologic examinations. This variability can lead to confusion as to how these tests should be used in the evaluation of GI bleeding. In this document, a panel of experts from the American College of Gastroenterology and Society of Abdominal Radiology provide a review of the radiologic examinations used to evaluate for GI bleeding including nomenclature, technique, performance, advantages, and limitations. A comparison of advantages and limitations relative to endoscopic examinations is also included. Finally, consensus statements and recommendations on technical parameters and utilization of radiologic techniques for GI bleeding are provided. © Radiological Society of North America and the American College of Gastroenterology, 2024. Supplemental material is available for this article. This article is being published concurrently in American Journal of Gastroenterology and Radiology. The articles are identical except for minor stylistic and spelling differences in keeping with each journal's style. Citations from either journal can be used when citing this article. See also the editorial by Lockhart in this issue.

The Role of Imaging for Gastrointestinal Bleeding: Consensus Recommendations From the American College of Gastroenterology and Society of Abdominal Radiology

Gastrointestinal (GI) bleeding is the most common GI diagnosis leading to hospitalization within the United States. Prompt diagnosis and treatment of GI bleeding is critical to improving patient outcomes and reducing high healthcare utilization and costs. Radiologic techniques including computed tomography angiography, catheter angiography, computed tomography enterography, magnetic resonance enterography, nuclear medicine red blood cell scan, and technetium-99m pertechnetate scintigraphy (Meckel scan) are frequently used to evaluate patients with GI bleeding and are complementary to GI endoscopy. However, multiple management guidelines exist which differ in the recommended utilization of these radiologic examinations. This variability can lead to confusion as to how these tests should be used in the evaluation of GI bleeding. In this document, a panel of experts from the American College of Gastroenterology and Society of Abdominal Radiology provide a review of the radiologic examinations used to evaluate for GI bleeding including nomenclature, technique, performance, advantages, and limitations. A comparison of advantages and limitations relative to endoscopic examinations is also included. Finally, consensus statements and recommendations on technical parameters and utilization of radiologic techniques for GI bleeding are provided.

A comparative study on the quality of in vivo labeled red blood cell radionuclide ventriculography images employing different freeze-dried reagents

Radionuclide ventriculography or Multi Gated Acquisition (MUGA) employing [ 99m Tc]Technetium red blood cell (RBC) labeling is considered the gold standard for cardiotoxicity assessments in cancer patients undergoing chemotherapy. This in-vivo RBC labeling technique involves the reduction of [ 99m Tc]Technetium by the stannous chloride present in freeze-dried reagent kits, with the pyrophosphate kit (PYP) being the most employed for this purpose. The literature, however, describes diethylenetriaminepentaacetic acid (DTPA) as an alternative to PYP, although a lack of comparative data from MUGA images between both reagents is noted. A retrospective cross-sectional observational study was conducted at the Brazilian National Cancer Institute Nuclear Medicine Service concerning 80 randomized MUGA images, 20 obtained employing DTPA between 2020 and 2023 and 60 obtained employing PYP between 2017 and 2020, applying the mean count per pixel (ct/pixel) and heart background (C/F) ratios as quality image indicators. Although the heart ct/pixel ratio was statistically lower in the DTPA images compared with PYP ( P  = 0.02), the C/F ratio was statistically similar when comparing both radiopharmaceuticals ( P  = 0.697). A semi-quantitative analysis of MUGA images obtained with DTPA and PYP indicates similar image quality, supporting the use of DTPA as an alternative to PYP without compromising diagnostic interpretations.

Gastrointestinal bleeding in children: diagnostic approach

Different conditions may underlie gastrointestinal bleeding (GIB) in children. The estimated prevalence of GIB in children is 6.4%, with spontaneous resolution in approximately 80% of cases. Nonetheless, the initial approach plays a pivotal role in determining the prognosis. The priority is the stabilization of hemodynamic status, followed by a systematic diagnostic approach. GIB can originate from either upper or lower gastrointestinal tract, leading to a broad differential diagnosis in infants and children. This includes benign and self-limiting disorders, alongside serious conditions necessitating immediate treatment. We performed a nonsystematic review of the literature, in order to describe the variety of conditions responsible for GIB in pediatric patients and to outline diagnostic pathways according to patients' age, suspected site of bleeding and type of bleeding which can help pediatricians in clinical practice. Diagnostic modalities may include esophagogastroduodenoscopy and colonoscopy, abdominal ultrasonography or computed tomography and, when necessary, magnetic resonance imaging. In this review, we critically assess these procedures, emphasizing their respective advantages and limitations concerning specific clinical scenarios.

The Accuracy of Computed Tomography Angiography Compared With Technetium-99m Labelled Red Blood Cell Scintigraphy for the Diagnosis and Localization of Acute Gastrointestinal Bleeding: A Systematic Review and Meta-Analysis

Imaging tests are commonly used as an initial or early investigation for patients presenting with suspected acute gastrointestinal bleeding (AGIB). However, controversy remains regarding which of two frequently used modalities, computed tomography angiography (CTA) or technetium-99m labelled red blood cell scintigraphy (RBCS), is most accurate. This systematic review and meta-analysis was performed to compare the accuracy of CTA and RBCS for the detection and localization of AGIB. Five electronic databases were searched with additional manual searching of reference lists of relevant publications identified during the search. Two reviewers independently performed screening, data extraction and methodological assessments. Where appropriate, the bivariate model was used for meta-analysis of sensitivities and specificities for the detection of bleeding and Freeman-Tukey double-arcsine transformation used for meta-analysis of proportions of correctly localized bleeding sites. Forty-four unique primary studies were included: twenty-two investigating CTA, seventeen investigating RBCS and five investigating both modalities. Meta-analysis produced similar pooled sensitivities; 0.83 (95% CI 0.74-0.90) and 0.84 (0.68-0.92) for CTA and RBCS respectively. Pooled specificity for CTA was higher than RBCS; 0.90 (0.72-0.97) and 0.84 (0.71-0.91) respectively. However, differences were not statistically significant. CTA was superior to RBCS in correctly localizing bleeding; pooled proportions of 1.00 (0.98-1.00) and 0.90 (0.83-0.96) respectively (statistically significant difference, P < 0.001). There is no evidence that CTA and RBCS have different diagnostic performance with respect to the detection of AGIB. However, CTA is superior to RBCS in terms of correctly localising the bleeding site, supporting usage of CTA over RBCS as the first line imaging investigation.

[Radiologic Diagnosis of Gastrointestinal Bleeding]

Gastrointestinal (GI) bleeding is not a single disease but a symptom and clinical manifestation of a broad spectrum of conditions in the GI tract. According to its clinical presentation, GI bleeding can be classified into overt, occult, and obscure types. Additionally, it can be divided into upper and lower GI bleeding based on the Treitz ligament. Variable disease entities, including vascular lesions, polyps, neoplasms, inflammation such as Crohn's disease, and heterotopic pancreatic or gastric tissue, can cause GI bleeding. CT and conventional angiographies and nuclear scintigraphy are all radiologic imaging modalities that can be used to evaluate overt bleeding. For the work-up of occult GI bleeding, CT enterography (CTE) can be the first imaging modality. For CTE, an adequate bowel distention is critical for obtaining acceptable diagnostic performance as well as minimizing false positives and negatives. Meckel's scintigraphy can be complementarily useful in cases where the diagnosis of CTE is suboptimal. For the evaluation of obscured GI bleeding, various imaging modalities can be used based on clinical status and providers' preferences.

M. de Rosales R. Direct Cell Radiolabeling for in Vivo Cell Tracking with PET and SPECT Imaging

The arrival of cell-based therapies is a revolution in medicine. However, its safe clinical application in a rational manner depends on reliable, clinically applicable methods for determining the fate and trafficking of therapeutic cells in vivo using medical imaging techniques─known as in vivo cell tracking. Radionuclide imaging using single photon emission computed tomography (SPECT) or positron emission tomography (PET) has several advantages over other imaging modalities for cell tracking because of its high sensitivity (requiring low amounts of probe per cell for imaging) and whole-body quantitative imaging capability using clinically available scanners. For cell tracking with radionuclides, ex vivo direct cell radiolabeling, that is, radiolabeling cells before their administration, is the simplest and most robust method, allowing labeling of any cell type without the need for genetic modification. This Review covers the development and application of direct cell radiolabeling probes utilizing a variety of chemical approaches: organic and inorganic/coordination (radio)chemistry, nanomaterials, and biochemistry. We describe the key early developments and the most recent advances in the field, identifying advantages and disadvantages of the different approaches and informing future development and choice of methods for clinical and preclinical application.

Axially torsional Meckel's diverticulum accompanied by small bowel volvulus: a case report

Small bowel volvulus secondary to Meckel’s diverticulum is rare, and a delayed diagnosis results in disastrous outcomes. Computed tomography is conducive to early differential diagnosis. In particular, a blind-ending pouch structure on CT always indicates Meckel’s diverticulum. Diverticulectomy with or without adjacent partial small intestinal resection is the standard treatment for symptomatic Meckel’s diverticulum. However, the therapy for asymptomatic Meckel’s diverticulum is controversial. Here, we report the case of a 20-year-old man who suffered intestinal obstruction secondary to small bowel volvulus caused by an axially torsional, gangrenous, and giant Meckel’s diverticulum. Diverticulectomy with partial intestinal resection was performed.

Unexplained anemia: A case report of metachronous adenocarcinoma arising in the transverse colon following right hemicolectomy for a primary cecal carcinoma

Metachronous colonic carcinomas arise from months to years after the resection of the first or index primary colorectal cancer. They are not a result of tumor recurrence or metastasis and likely arise as a result of the field cancerization effect. This report presents the case of a 63-year-old male patient without family history of a colorectal cancer but had an index primary adenocarcinoma of the cecum (stage IIIC) five years ago that was treated with surgical resection and adjuvant radiotherapy and chemotherapy. He presented with fatigue and anemia of 6-month duration secondary to recurrent melena, and the specific cause of which remained obscure despite intensive diagnostic workup. Recurrence of a malignancy at the previous anastomosis site was ruled out. The patient continued to have recurrent and intermittent gastrointestinal bleeding until a nuclear red blood cell scan detected a bleeding spot in the epigastric region, which actually turned out to be a second primary carcinoma (stage I) arising from an adenoma in the transverse colon. The patient underwent a left colectomy with ileosigmoid anastomosis formation. During a two-month postoperative follow-up, the patient did not experience any episode of melena or anemia. Even though metachronous colon cancers rarely present with a recurrent and intermittent gastrointestinal bleeding with melena, an aggressive workup must be aimed at ruling out a second independent malignancy in patients who are in remission after an index primary colorectal cancer resection through hemicolectomy. Any neoteric lesion found on colonoscopy in such cases should be dealt with a higher degree of suspicion. Therefore, the need for surveillance colonoscopy as recommended by the National Comprehensive Cancer Network guidelines is imperative and should be practiced in resource-limited countries.

RXH-Reactive 18F-Vinyl Sulfones as Versatile Agents for PET Probe Construction

Efficient radiolabeling reactions are important chemical tools in biomedical research especially in probe construction. Herein, three ¹⁸F-labeled vinyl sulfones were prepared. In particular, ¹⁸F-PEG1-VS (((2-(2-(fluoro-¹⁸F)ethoxy)ethyl)sulfonyl)ethane) could not only allow chemoselective labeling of bioactive molecules containing -XH (X = S, NH) groups, but also react with red blood cells both in vitro and in living mice for potential cell tracking applications. In addition, these hydrophilic agents were found to cross the blood brain barrier (BBB) efficiently and localize at the cerebellum region. In summary, ¹⁸F-labeled vinyl sulfones provide a versatile platform for PET probe construction.

Meckel's Diverticulum Imaging

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99mTc-RBC SPECT/CT for Duodenal Bleeding Point Detection

This is a case of a 63-year-old man who presented with acute melena and low hemoglobin. Upper and lower gastrointestinal evaluations failed to localize the bleeding focus. Tc-RBC planar scintigraphy identified 2 sites of suspected bleeding in the lower abdomen area. Subsequent SPECT/CT was performed and identified the precise main focus of active bleeding, the second and third parts of the duodenum, and also described the blood accumulation in the jejunum. Esophagogastroduodenoscopy was immediately performed, and results confirmed spurting blood from the small vessel with multiple ulcers in the second part of the duodenum.

Time to Catheter Angiography for Gastrointestinal Bleeding after Prior Positive Investigation Does Not Affect Bleed Identification

Objective:

To determine, time to angiography for patients with positive gastrointestinal bleeding (GIB) on prior investigation (endoscopy [ES], nuclear medicine [NM] Tc99m red blood cells (RBC) scan, or computed tomography angiography), affects angiographic bleed identification.

Materials and Methods:

Visceral Angiograms performed from January 2012 to August 2017 were evaluated. Initial angiograms performed for GIB were included in the study. Exclusion criteria included recent abdominal surgery or procedure (30 days), empiric embolization (embolization without visualized active bleeding), and use of vasodilators, or subsequent angiogram. Timing and results of ES, NM Tc99m RBC scan, or computed tomography angiogram and catheter angiogram were recorded. In addition, age, gender, angiogram time, anti- platelet therapy, anti-coagulation therapy, bleed location, international normalized ratio, and units of packed RBCs received in the 24 h before catheter angiography were included in the study.

Results:

One hundred and seventy angiograms were included in the final analysis. Forty-three angiograms resulted in the identification of an active bleed (68.9 years, and 67.4% male). All of these patients were embolized successfully. One hundred and twenty-seven angiograms failed to identify an active bleed (70.4 years, and 49.6% male). No significance was found across the two groups with respect to time from prior positive investigation. Receiver operating characteristic analysis demonstrated that units of packed RBCs received in the preceding 24 h were correlated with positive bleed identification on catheter angiography.

Conclusion:

Time to angiography from prior positive investigation, including ES, NM Tc99m RBC scan, or computed tomography angiogram does not correlate with positive angiographic outcomes. Increasing units of packed RBCs administered in the 24 h before angiogram do correlate with positive angiographic findings.

Acute Painless Lower Gastrointestinal Bleed That Mimics Meckel Diverticulum

OBJECTIVE

We describe a case of gastrointestinal duplication cyst with heterotopic gastric mucosa presenting with hematochezia.

CASE

The patient was a previously healthy 2-month-old girl presenting with passing fresh blood in the diaper without distress or abdominal discomfort. She was evaluated for colic prior to this episode and discharged home. Meckel scan was positive, and surgeons performed an exploratory laparotomy to identify a jejunal duplication cyst. The infant had an uneventful recovery and was discharged home.

CONCLUSIONS

Gastrointestinal duplication cyst is an uncommon condition and can rarely present with lower gastrointestinal bleed with heterotopic gastric mucosa.

Two decades of SPECT/CT - the coming of age of a technology: An updated review of literature evidence

PURPOSE

Single-photon emission computed tomography (SPECT) combined with computed tomography (CT) was introduced as a hybrid SPECT/CT imaging modality two decades ago. The main advantage of SPECT/CT is the increased specificity achieved through a more precise localization and characterization of functional findings. The improved diagnostic accuracy is also associated with greater diagnostic confidence and better inter-specialty communication.

METHODS

This review presents a critical assessment of the relevant literature published so far on the role of SPECT/CT in a variety of clinical conditions. It also includes an update on the established evidence demonstrating both the advantages and limitations of this modality.

CONCLUSIONS

For the majority of applications, SPECT/CT should be a routine imaging technique, fully integrated into the clinical decision-making process, including oncology, endocrinology, orthopaedics, paediatrics, and cardiology. Large-scale prospective studies are lacking, however, on the use of SPECT/CT in certain clinical domains such as neurology and lung disorders. The review also presents data on the complementary role of SPECT/CT with other imaging modalities and a comparative analysis, where available.

The role of imaging in gastrointestinal bleed

Gastrointestinal (GI) bleed accounts for approximately 20% of emergency visits; 2% of hospital admissions and its incidence has been increasing. In patients where the GI bleed does not stop spontaneously, intervention is required to identify the source of bleeding and stop the hemorrhage. Although identifying the source of bleeding can be challenging due to the vast number of underlying etiologies, radiology plays a vital role in patients where endoscopy and/or medical management fail. Radiology offers both non-invasive and invasive options for the diagnosis as well as management of GI bleeds. Scintigraphy and computed tomography angiography (CTA) are the most important non-invasive imaging tests that can identify presence of and help locate the site of bleeding and are used when the patient is hemodynamically stable. If the patient is hemodynamically unstable, conventional angiography (CA) allows diagnosis of the presence, site of bleeding as well as the means of treating the bleed by embolization. Our review article focuses on the various etiologies of GI bleed, the role of imaging in diagnosis as well as treatment of these patients based on the underlying etiologies, the merits and disadvantages of each of these modalities with emphasis on triaging patients for the most appropriate imaging test to guide the most suitable management.

Small Bowel Gastrointestinal Bleeding Diagnosis and Management-A Narrative Review

Background: Small bowel bleeding accounts for 5-10% of all gastrointestinal bleeding. Despite advances in imaging, endoscopy and minimally invasive therapeutic techniques, its diagnosis and treatment remains a challenge and a standardized algorithm for approaching suspected small bowel bleeding remains elusive. Furthermore, the choice of investigation is subject to timing of presentation and accessibility to investigations. The aim of this study was to construct a narrative review of recent literature surrounding the diagnosis and management of small bowel bleeding. Methods: A literature review was conducted examining the database pubmed with the following key words and Boolean operators: occult GI bleed OR mesenteric bleed OR gastrointestinal hemorrhage OR GI hemorrhage AND management. Articles were selected and reviewed based on relevance to the research topic. Where necessary, the full text was sought to further assess relevance. Results: In overt GI bleeding, CT angiography and red cell scintigraphy are both feasible and reliable diagnostic imaging modalities if standard endoscopy is negative. Red cell scintigraphy may be advantageous through detection of lower bleeding rates but it is subject to availability. Overt bleeding and a positive CT angiogram or red cell scan improves the diagnostic yield of formal angiography ± embolization. Video capsule endoscopy or double balloon endoscopy can be considered in occult GI bleeding following normal upper and lower endoscopy. Conclusions: Small bowel bleeding remains a rare but significant diagnostic and therapeutic challenge. Technological advances in diagnostics have aided evaluation but have not broadened the range of therapeutic interventions.

Development of 99mTc-Labeled Human Serum Albumin with Prolonged Circulation by Chelate-then-Click Approach: A Potential Blood Pool Imaging Agent

Technetium-99m-labeled human serum albumin (^99mTc-HSA) has been utilized as a blood pool imaging agent in the clinic for several decades. However, ^99mTc-HSA has a short circulation time, which is a critical shortcoming for a blood pool imaging agent. Herein, we developed a novel ^99mTc-labeled HSA with a long circulation time using click chemistry and a chelator, 2,2'-dipicolylamine (DPA), (^99mTc-DPA-HSA). Specifically, we examined the feasibility of copper-free strain-promoted alkyne-azide cycloaddition (SPAAC) for the incorporation of HSA to the [^99mTc (CO)₃(H₂O)₃]⁺ system by adopting a chelate-then-click approach. In this strategy, a potent chelate system, azide-functionalized DPA, was first complexed with [^99mTc (CO)₃(H₂O)₃]⁺, followed by the SPAAC click reaction with azadibenzocyclooctyne-functionalized HSA (ADIBO-HSA) under biocompatible conditions. Radiolabeling efficiency of azide-functionalized DPA (^99mTc-DPA) was >98%. Click conjugation efficiency of ^99mTc-DPA with ADIBO-HSA was between 76 and 99% depending on the number of ADIBO moieties attached to HSA. In whole-body in vivo single photon emission computed tomography images, the blood pool uptakes of ^99mTc-DPA-HSA were significantly enhanced compared to those of ^99mTc-HSA at 10 min, 2, and 6 h after the injection ( P < 0.001, 0.025, and 0.003, respectively). Furthermore, the blood activities of ^99mTc-DPA-HSA were 8 times higher at 30 min and 10 times higher at 3 h after the injection compared to those of conventional ^99mTc-HSA in ex vivo biodistribution experiment. The results exhibit the potential of ^99mTc-DPA-HSA as a blood pool imaging agent and further illustrate the promise of the pre-labeling SPAAC approach for conjugation of heat-sensitive biological targeting vectors with [^99mTc (CO)₃(H₂O)₃]⁺.

Independent usefulness of flow phase 99mTc-red blood cell scintigraphy in predicting the results of angiography in acute gastrointestinal bleeding

OBJECTIVE:

In acute gastrointestinal bleeding, despite positive dynamic phase ⁹⁹mTc-red blood cell scintigraphy, invasive catheter angiography (CA) is frequently negative. In this study, we investigated the value of flow phase scintigraphy in predicting extravasation on CA.

METHODS:

Institutional review board approval with a waiver of informed consent was obtained for this retrospective study. A total of 173 scintigraphy procedures performed in 145 patients with GIB between January 2013 and August 2014 were analysed. Scintigraphy had two phases: flow (1 image/s for 1 min) followed by dynamic (1 image/30 s for 1 h). Patients who underwent CA within 24 hours of positive scintigraphy were assessed. Each scintigraphy phase was randomly and independently reviewed by two nuclear medicine physicians blinded to the outcomes of the other phase and of CA.

RESULTS:

A total of 42 patients (29%) had positive scintigraphy. Of these patients, 29 underwent CA, and extravasation was seen in 6 (21%). In all, dynamic phase scintigraphy was positive. 13 of the 29 patients also had positive flow phase scintigraphy. The sensitivity, specificity, positive-predictive value, and negative-predictive value of flow phase scintigraphy for extravasation on CA were 100, 70, 46, and 100%, respectively. Specificity and positive predictive value were higher when CA was performed within 4 hours of positive flow phase scintigraphy.

CONCLUSIONS:

Negative flow phase scintigraphy can identify patients who will not benefit from CA despite positive dynamic phase scintigraphy. The likelihood of extravasation on CA is higher when performed soon after positive flow phase scintigraphy.

ADVANCES IN KNOWLEDGE:

Negative flow phase scintigraphy identifies patients who will not benefit from invasive catheter angiography despite positive results on subsequent dynamic phase scintigraphy. Increasing the delay between positive red blood cell scintigraphy and catheter angiography progressively reduces the likelihood of identifying extravasation, which is required to target embolization.

Inverted Meckel’s diverticulum: Two case reports and a review of the literature

Gastrointestinal surgeons seldom encounter inverted Meckel’s diverticulum in their clinical practice. We describe two cases of inverted Meckel’s diverticulum. If the patient has a disease-related complication such as intussusception, as with our first case, it can be easily detected. However, if the patient has subacute or chronic symptoms, as with our second case, the diagnosis might be delayed. Regardless of the disease-related complication, intussusception of inverted Meckel’s diverticulum can be easily managed with laparoscopic single-port surgery.

Successful Localization of the Source of Hemorrhage in Patient with Post-Whipple Surgery by 99mTc-Labelled Red Blood Cell Scintigraphy

Gastrointestinal Bleeding Scintigraphy (GIBS) of ^99mTc-labelled red blood cells is a relatively simple examination to perform, with high diagnostic accuracy and a relatively lower radiation dose. A positive scan can either suggest surgery without further investigation or can indicate angiography, a more targeted procedure. Whipple pancreatoduodenectomy is most often performed for tumors of the head of the pancreas. Pancreatoduodenectomy has 30%–40% morbidity and mortality, and while post-pancreatoduodenectomy hemorrhage is seen in less than 10% of patients, it accounts for 11%–38% mortality. The role of imaging in patients to detect relative hemodynamic stability is essential. Computed tomography angiography (CTA) shows the cause, site, and nature of bleeding, while digital subtraction angiography (DSA) has a diagnostic as well as a therapeutic role. We present a patient who presented with active gastrointestinal bleeding (GI) bleeding after undergoing a Whipple procedure, to highlight the role of GIBS in the successful localization of a bleeding site and the guidance of digital DSA in the embolization and control of the active bleeding.

Radiologic Assessment of Gastrointestinal Bleeding

Gastrointestinal (GI) bleeding represents a broad differential of disease throughout the GI tract. The proper diagnostic evaluation of patients presenting with symptoms of GI bleeding depends on the overall clinical acuity and suspected source locations. The radiologic assessment of these patients is centered around computed tomography (CT) angiography, CT enterography, conventional angiography, and nuclear scintigraphy.

Imaging Workup of Acute and Occult Lower Gastrointestinal Bleeding

Lower gastrointestinal bleeding is defined as occurring distal to the ligament of Treitz and presents as hematochezia, melena, or with anemia and positive fecal occult blood test. Imaging plays a pivotal role in the localization and treatment of lower gastrointestinal bleeds. Imaging tests in the workup of acute lower gastrointestinal bleeding include computed tomography (CT) angiography, nuclear medicine scintigraphy, and conventional catheter angiography. Catheter angiography can also be used to deliver treatment. Imaging tests in the workup of occult lower gastrointestinal bleeding include CT enterography and nuclear medicine Meckel scan.

One-pot synthesis and biodistribution of fluorine-18 labeled serum albumin for vascular imaging

INTRODUCTION

Equilibrium single-photon radionuclide imaging methods for assessing cardiac function and the integrity of the vascular system have long been in use for both clinical and research purposes. However, positron-emitting blood pool agents that could provide PET equivalents to these (and other) clinical procedures have not yet been adopted despite technical imaging advantages offered by PET. Our goal was to develop a PET blood pool tracer that not only meets necessary in vivo biological requirements but can be produced with an uncomplicated and rapid synthesis method which would facilitate clinical translation. Herein, albumin labeled with fluorine-18 was synthesized using a one-pot method and evaluated in vitro and in vivo in rats.

METHODS

A ligand (NODA-Bz-TFPE), containing NODA attached to a tetrafluorophenylester (TFPE) via a phenyl linker (Bz), was labeled with aluminum fluoride (Al[18F]F). Conjugation of the serum albumin with the ligand (Al[18F]F-NODA-Bz-TFPE), followed by purification (size exclusion chromatography), yielded the final product (Al[18F]F-NODA-Bz-RSA/HSA). In vitro stability was evaluated in human serum albumin by HPLC. Rat biodistributions and whole-body PET imaging over a 4 h time course were used for the in vivo evaluation.

RESULTS

This synthesis exhibited an overall radiochemical yield of 45 ± 10% (n = 30), a 50-min radiolabeling time, a radiochemical purity >99% and apparent stability up to 4 h in human serum. Blood had the highest retention of Al[18F]F-NODA-Bz-RSA at all times with a blood half-life of 5.2 h in rats. Al[18F]F-NODA-Bz-RSA distribution in most rat tissues remained relatively constant for up to 1 h, indicating that the tissue radioactivity content represents the respective tissue plasma volume. Dynamic whole-body PET images were in agreement with these findings.

CONCLUSIONS

A new ligand has been developed and radiolabeled with Al[18F]F that allows rapid (50-min) preparation of fluorine-18 serum albumin in one-pot. In addition to increased synthetic efficiency, the construct appears to be metabolically stable in rats. This method could encourage wider use of PET to quantify cardiac function and tissue vascular integrity in both research and clinical settings.

Magnetic Particle Imaging for Highly Sensitive, Quantitative, and Safe in Vivo Gut Bleed Detection in a Murine Model

Gastrointestinal (GI) bleeding causes more than 300 000 hospitalizations per year in the United States. Imaging plays a crucial role in accurately locating the source of the bleed for timely intervention. Magnetic particle imaging (MPI) is an emerging clinically translatable imaging modality that images superparamagnetic iron-oxide (SPIO) tracers with extraordinary contrast and sensitivity. This linearly quantitative modality has zero background tissue signal and zero signal depth attenuation. MPI is also safe: there is zero ionizing radiation exposure to the patient and clinically approved tracers can be used with MPI. In this study, we demonstrate the use of MPI along with long-circulating, PEG-stabilized SPIOs for rapid in vivo detection and quantification of GI bleed. A mouse model genetically predisposed to GI polyp development (ApcMin/+) was used for this study, and heparin was used as an anticoagulant to induce acute GI bleeding. We then injected MPI-tailored, long-circulating SPIOs through the tail vein, and tracked the tracer biodistribution over time using our custom-built high resolution field-free line (FFL) MPI scanner. Dynamic MPI projection images captured tracer accumulation in the lower GI tract with excellent contrast. Quantitative analysis of the MPI images show that the mice experienced GI bleed rates between 1 and 5 μL/min. Although there are currently no human scale MPI systems, and MPI-tailored SPIOs need to undergo further development and evaluation, clinical translation of the technique is achievable. The robust contrast, sensitivity, safety, ability to image anywhere in the body, along with long-circulating SPIOs lends MPI outstanding promise as a clinical diagnostic tool for GI bleeding.

Emergency transcatheter arterial embolization for massive gastrointestinal arterial hemorrhage

To evaluate the different arteriographic manifestations of acute arterial massive hemorrhage of the gastrointestinal (GI) tract and the efficacy of emergency transcatheter arterial embolization (ETAE).A total of 88 patients with acute massive GI bleeding who experienced failure of initial endoscopy and/or conservative treatment were referred to our interventional department for acute GI arteriography from January 2007 to June 2015. After locating the source of bleeding, appropriate embolic agents, such as spring coil, hydroxyl methyl acrylic acid gelatin microspheres, polyvinyl alcohol (PVA) particles, etc., were used to embolize the targeted vessels. The angiographic manifestations and the effects of embolization of acute arterial massive hemorrhage of the GI tract were retrospectively analyzed.Of the 88 patients, 54 were diagnosed with arterial hemorrhage of the upper GI tract and 34 with arterial hemorrhage of the lower GI tract. Eighty cases were associated with positive angiography, which showed the following: contrast extravasation (only); gastroduodenal artery stenosis; pseudoaneurysm (only); pseudoaneurysm rupture with contrast extravasation; pseudoaneurysms merged with intestinal artery stenosis; GI angiodysplasia; and tumor vascular bleeding. Eight cases were diagnosed with negative angiography. Seven-two patients underwent successful hemostasis, and a total of 81 arteries were embolized. The technical and clinical success rates (no rebleeding within 30 days) in performing transcatheter embolization on patients with active bleeding were 100% and 84.71%, respectively (72 of 85). Within 30 days, the postoperative rebleeding rate was 15.29% (13/85). Of these rebleeding cases, 2 patients were formerly treated with "blind embolization," 7 underwent interventional embolic retreatment, and 3 had surgical operations. All cases were followed-up for 1 month, and 3 patients died from multiple organ failure. No serious complications such as bowel ischemia necrosis were observed.ETAE is a safe, effective, and minimally invasive treatment; because of the diversified arteriographic manifestations of acute GI hemorrhage, the proper selection of embolic agents and the choice of reasonable embolization method are essential for successful hemostasis.

Pelvic Meckel's Diverticulum Mimicking Bladder on Meckel Scan; The Impact of Quality Control and Technical Issues

Quality control and technical issues are essential for high-quality imaging. An important technical parameter of image acquisition is selecting zoom factor according to camera field-of-view dimensions and patient's body size. Here, we present a case of atypically located Meckel's diverticulum mimicking bladder on Meckel scan.

18F-FDG-labeled red blood cell PET for blood-pool imaging: preclinical evaluation in rats

Background

Red blood cells (RBCs) labeled with single-photon emitters have been clinically used for blood-pool imaging. Although some PET tracers have been introduced for blood-pool imaging, they have not yet been widely used. The present study investigated the feasibility of labeling RBCs with ¹⁸F-2-deoxy-2-fluoro-D-glucose (¹⁸F-FDG) for blood-pool imaging with PET.

RBCs isolated from venous blood of rats were washed with glucose-free phosphate-buffered saline and labeled with ¹⁸F-FDG. To optimize labeling efficiency, the effects of glucose deprivation time and incubation (labeling) time with ¹⁸F-FDG were investigated. Post-labeling stability was assessed by calculating the release fraction of radioactivity and identifying the chemical forms of ¹⁸F in the released and intracellular components of ¹⁸F-FDG-labeled RBCs incubated in plasma. Just after intravenous injection of the optimized autologous ¹⁸F-FDG-labeled RBCs, dynamic PET scans were performed to evaluate in vivo imaging in normal rats and intraabdominal bleeding models (temporary and persistent bleeding).

Results

The optimal durations of glucose deprivation and incubation (labeling) with ¹⁸F-FDG were 60 and 30 min, respectively. As low as 10% of ¹⁸F was released as the form of ¹⁸F-FDG from ¹⁸F-FDG-labeled RBCs after a 60-min incubation. Dynamic PET images of normal rats showed strong persistence in the cardiovascular system for at least 120 min. In the intraabdominal bleeding models, ¹⁸F-FDG-labeled RBC PET visualized the extravascular blood clearly and revealed the dynamic changes of the extravascular radioactivity in the temporary and persistent bleeding.

Conclusions

RBCs can be effectively labeled with ¹⁸F-FDG and used for blood-pool imaging with PET in rats.

Electronic supplementary material

The online version of this article (doi:10.1186/s13550-017-0266-3) contains supplementary material, which is available to authorized users.