Conventional Morphological Imaging Research Articles

Multimodal positron emission tomography (PET) imaging in non-oncologic musculoskeletal radiology.

Musculoskeletal (MSK) disorders are associated with large impacts on patient's pain and quality of life. Conventional morphological imaging of tissue structure is limited in its ability to detect pain generators, early MSK disease, and rapidly assess treatment efficacy. Positron emission tomography (PET), which offers unique capabilities to evaluate molecular and metabolic processes, can provide novel information about early pathophysiologic changes that occur before structural or even microstructural changes can be detected. This sensitivity not only makes it a powerful tool for detection and characterization of disease, but also a tool able to rapidly assess the efficacy of therapies. These benefits have garnered more attention to PET imaging of MSK disorders in recent years. In this narrative review, we discuss several applications of multimodal PET imaging in non-oncologic MSK diseases including arthritis, osteoporosis, and sources of pain and inflammation. We also describe technical considerations and recent advancements in technology and radiotracers as well as areas of emerging interest for future applications of multimodal PET imaging of MSK conditions. Overall, we present evidence that the incorporation of PET through multimodal imaging offers an exciting addition to the field of MSK radiology and will likely prove valuable in the transition to an era of precision medicine.

Diffusion tensor imaging derived metrics in high grade glioma and brain metastasis differentiation

Background: Pretreatment differentiation between glioblastoma and metastasis is a frequently encountered dilemma in neurosurgical practice. Distinction is required for precise planning of resection or radiotherapy, and also for defining further diagnostic procedures. Morphology and spectroscopy imaging features are not specific and frequently overlap. This limitation of magnetic resonance imaging and magnetic resonance spectroscopy was the reason to initiate this study. The aim of the present study was to determine whether the dataset of diffusion tensor imaging metrics contains information which may be used for the distinction between primary and secondary intra-axial neoplasms. Methods: Two diffusion tensor imaging parameters were measured in 81 patients with an expansive, ring-enhancing, intra-axial lesion on standard magnetic resonance imaging (1.5 T system). All tumors were histologically verified glioblastoma or secondary deposit. For qualitative analysis, two regions of interest were defined: intratumoral and immediate peritumoral region (locations 1 and 2, respectively). Fractional anisotropy and mean difusivity values of both groups were compared. Additional test was performed to determine if there was a significant difference in mean values between two locations. Results: A statistically significant difference was found in fractional anisotropy values among two locations, with decreasing values in the direction of neoplastic infiltration, although such difference was not observed in fractional anisotropy values in the group with secondary tumors. Mean difusivity values did not appear helpful in differentiation between these two entities. In both groups there was no significant difference in mean difusivity values, neither in intratumoral nor in peritumoral location. Conclusion: The results of our study justify associating the diffusion tensor imaging technique to conventional morphologic magnetic resonance imaging as an additional diagnostic tool for the distinction between primary and secondary intra-axial lesions. Quantitative analysis of diffusion tensor imaging metric, in particular measurement of fractional anisotropy in peritumoral edema facilitates accurate diagnosis.

The Value of 18F-FDG-PET-CT Imaging in Treatment Evaluation of Colorectal Liver Metastases: A Systematic Review.

(1) Background: Up to 50% of patients with colorectal cancer either have synchronous colorectal liver metastases (CRLM) or develop CRLM over the course of their disease. Surgery and thermal ablation are the most common local treatment options of choice. Despite development and improvement in local treatment options, (local) recurrence remains a significant clinical problem. Many different imaging modalities can be used in the follow-up after treatment of CRLM, lacking evidence-based international consensus on the modality of choice. In this systematic review, we evaluated 18F-FDG-PET-CT performance after surgical resection, thermal ablation, radioembolization, and neoadjuvant and palliative chemotherapy based on current published literature. (2) Methods: A systematic literature search was performed on the PubMed database. (3) Results: A total of 31 original articles were included in the analysis. Only one suitable study was found describing the role of 18F-FDG-PET-CT after surgery, which makes it hard to draw a firm conclusion. 18F-FDG-PET-CT showed to be of additional value in the follow-up after thermal ablation, palliative chemotherapy, and radioembolization. 18F-FDG-PET-CT was found to be a poor to moderate predictor of pathologic response after neoadjuvant chemotherapy. (4) Conclusions: 18F-FDG-PET-CT is superior to conventional morphological imaging modalities in the early detection of residual disease after thermal ablation and in the treatment evaluation and prediction of prognosis during palliative chemotherapy and after radioembolization, and 18F-FDG-PET-CT could be considered in selected cases after neoadjuvant chemotherapy and surgical resection.

Additional Value of [18F]FDG PET or PET/CT for Response Assessment of Patients with Gastrointestinal Stromal Tumor Undergoing Molecular Targeted Therapy: A Meta-Analysis.

To assess the additional value of 2-deoxy-2-[18F] fluoro-d-glucose ([18F]FDG) positron emission tomography (PET) or PET/CT over conventional morphological imaging techniques in the treatment response assessment of gastrointestinal stromal tumor (GIST) to molecular targeted therapy (MTT), we performed a meta-analysis of all the available studies to compare the predictive value of [18F]FDG PET or PET/CT and conventional imaging techniques for assessing the response to MTT in GIST. We determined the sensitivities and specificities across studies, we calculated the positive and negative likelihood ratios (LR) and made summary receiver operating characteristic curves (SROC) using hierarchical regression models. Pooled analysis included 4 studies comprising 88 patients. The performance characteristics in [18F]FDG PET or PET/CT and CT were as follows: sensitivity, 89% (95% confidence interval (CI) 78, 95), 52% (39, 64); specificity, 65% (44, 83), 92% (75, 99); diagnostic odds ratios (DOR), 5.8 (2.0, 16.8 4.9 (1.5, 16.1); positive LR, 1.9 (1.1, 3.4), 3.0 (1.1, 8.1); and negative LR, 0.23 (0.03, 1.6), 0.66 (0.42, 1.0), respectively. In SROC curves, the area under the curve (AUC) was 0.81 (SE, 0.11) and 0.71 (SE, 0.13) and the Q* index was 0.74 and 0.66, respectively. [18F]FDG PET/CT had higher sensitivity, while DOR and SROC curves showed better diagnostic performance in [18F]FDG PET and PET/CT studies as compared to CT.

Therapeutic response assessment in pancreatic ductal adenocarcinoma: society of abdominal radiology review paper on the role of morphological and functional imaging techniques.

Pancreatic ductal adenocarcinoma (PDA) is the third leading cause of cancer-related death in the United States and is projected to be the second by 2030. Systemic combination chemotherapy is considered an essential first-line treatment for the majority of patients with PDA, in both the neoadjuvant and palliative settings. In addition, a number of novel therapies are being tested in clinical trials for patients with advanced PDA. In all cases, accurate and timely assessment of treatment response is critical to guide therapy, reduce drug toxicities and cost from a failing therapy, and aid adaptive clinical trials. Conventional morphological imaging has significant limitations, especially in the context of determining primary tumor response and resectability following neoadjuvant therapies. In this article, we provide an overview of current therapy options for PDA, highlight several morphological imaging findings that may be helpful to reduce over-staging following neoadjuvant therapy, and discuss a number of emerging imaging, and non-imaging, tools that have shown promise in providing a more precise quantification of disease burden and treatment response in PDA.

The Value of Quantitative Musculoskeletal Imaging.

Musculoskeletal imaging is mainly based on the subjective and qualitative analysis of imaging examinations. However, integration of quantitative assessment of imaging data could increase the value of imaging in both research and clinical practice. Some imaging modalities, such as perfusion magnetic resonance imaging (MRI), diffusion MRI, or T2 mapping, are intrinsically quantitative. But conventional morphological imaging can also be analyzed through the quantification of various parameters. The quantitative data retrieved from imaging examinations can serve as biomarkers and be used to support diagnosis, determine patient prognosis, or monitor therapy.We focus on the value, or clinical utility, of quantitative imaging in the musculoskeletal field. There is currently a trend to move from volume- to value-based payments. This review contains definitions and examines the role that quantitative imaging may play in the implementation of value-based health care. The influence of artificial intelligence on the value of quantitative musculoskeletal imaging is also discussed.

Theranostics and hybrid imaging for somatostatin receptor-expressing tumors

Conventional imaging tests like computed tomography (CT) cannot visualize somatostatin receptor (SSTR) expression on the tumor cell surface. For imaging of SSTR-expressing tumors conventional morphological imaging tests such as CT or magnetic resonance imaging (MRI) are employed. Molecular imaging of SSTR expression on the tumor cell surface, in particular by using (whole body) single photon emission computed tomography (SPECT) and positron emission tomography (PET), are considered the current standard of care. Only the use of CT enables for exact localization of putative sites of disease (hybrid imaging). Hybrid SPECT/CT and PET/CT are of utmost importance for staging and monitoring of treatment efficacy. SSTR-PET is superior to SPECT and the PET radiotracer 68Ga-DOTATATE has been approved in multiple countries. In addition, SSTR positivity revealed by SPECT or PET pave the way for apeptide receptor radionuclide therapy (PRRT). Such atheranostic approach enables for systemic or locoregional radiation with β‑emitting radionuclides, which are linked to the identical amino acid peptide used for PET or SPECT imaging. The prospective, randomized Netter‑1 trial has shown significant benefit for patients receiving PRRT. Acombined use of conventional and functional imaging tests is superior to conventional imaging alone and allows for identification of suitable candidates for atheranostic approach. In case of clinical suspicion or after having obtained histological evidence, hybrid SSTR-SPECT/CT or -PET/CT should be performed, preferably in adedicated molecular imaging center.

Prediction and evaluation value of functional imaging technique in neoadjuvant chemoradiotherapy of locally advanced rectal cancer

For locally advanced rectal cancer, neoadjuvant chemoradiotherapy, followed by surgery and postoperative adjuvant chemotherapy has become a standard treatment mode. Neoadjuvant chemoradiotherapy can induce the tumors to shrink to different extent. Partial patients can obtain complete remission validated by postoperative pathological examination, which contributes to increasing the probability of radical surgery for rectal cancer patients, reducing the recurrence rate and improving the long-term clinical prognosis. In recent years, the prediction and evaluation of the clinical efficacy of neoadjuvant therapy has captivated widespread attentions from clinicians. In terms of imaging methods, conventional morphological imaging techniques cannot accurately assess the clinical efficacy of neoadjuvant chemoradiotherapy, whereas DWI-MRI, DCE-MRI, PET-CT and other functional imaging techniques can not only reflect the degree of tumor shrinkage, but also reveal the changes in the functional metabolism of tumors before and after treatment and yield higher accuracy. In this article, recent application of imaging techniques in the evaluation of clinical efficacy of neoadjuvant chemoradiotherapy for rectal cancer was reviewed. Key words: Rectal neoplasms/neoadjuvant chemoradiotherapy; Functional imaging; Prediction and evaluation

PET/CT and Bone Scintigraphy: Metabolic Results in Musculoskeletal Lesions

This review aimed to provide an overview on findings from metabolic imaging modalities such as bone scintigraphy and positron emission tomography–computed tomography (PET/CT) in musculoskeletal lesions. It is conceivable that methods assessing metabolism of bone tumors, combined with the morphological assessment, could enhance the possibility for a personalized therapy with particular emphasis to malignant neoplasms. The assessment of bone tumors by conventional scintigaphic and morphological imaging has been recently integrated with the morpho-metabolic appraisal obtained by PET/CT systems. Increasing availability of this diagnostic modality has been shown to stratify properly the patients and the findings correlate well with outcome. Moreover, new tracers are being implemented in the study of musculoskeletal lesions by PET/CT while the new volumetric parameters used to identify the lesions hold great promise. Results from PET/CT are associated with tumor grading and histopathology in bone malignant lesions and they could be of value for implementing treatment strategy. Additionally, the metabolic assessment has been demonstrated useful for predicting surgical response and patients’ outcome.

Functional MR imaging in gynecologic malignancies: current status and future perspectives.

Using functional MR imaging techniques, we can approach the functional assessment of gynecologic malignancies. Among them, diffusion-weighted imaging (DWI) and dynamic contrast-enhanced MR imaging (DCE-MRI) are two important techniques. This article provides an overview of functional MR imaging techniques, focusing DWI and DCE-MRI on clinical application in gynecologic malignancies. Functional MR imaging techniques play an important role in detection, characterization, staging, treatment response, and outcome prediction, as well as providing conventional morphologic imaging. Familiarity with the characteristics and imaging features of functional MR imaging in gynecologic malignancies will facilitate prompt and accurate diagnosis and treatment.

Interventional Molecular Imaging.

Although molecular imaging has had a dramatic impact on diagnostic imaging, it has only recently begun to be integrated into interventional procedures. Its significant impact is attributed to its ability to provide noninvasive, physiologic information that supplements conventional morphologic imaging. The four major interventional opportunities for molecular imaging are, first, to provide guidance to localize a target; second, to provide tissue analysis to confirm that the target has been reached; third, to provide in-room, posttherapy assessment; and fourth, to deliver targeted therapeutics. With improved understanding and application of(18)F-FDG, as well as the addition of new molecular probes beyond(18)F-FDG, the future holds significant promise for the expansion of molecular imaging into the realm of interventional procedures.

General review of magnetic resonance elastography.

Magnetic resonance elastography (MRE) is an innovative imaging technique for the non-invasive quantification of the biomechanical properties of soft tissues via the direct visualization of propagating shear waves in vivo using a modified phase-contrast magnetic resonance imaging (MRI) sequence. Fundamentally, MRE employs the same physical property that physicians utilize when performing manual palpation - that healthy and diseased tissues can be differentiated on the basis of widely differing mechanical stiffness. By performing "virtual palpation", MRE is able to provide information that is beyond the capabilities of conventional morphologic imaging modalities. In an era of increasing adoption of multi-parametric imaging approaches for solving complex problems, MRE can be seamlessly incorporated into a standard MRI examination to provide a rapid, reliable and comprehensive imaging evaluation at a single patient appointment. Originally described by the Mayo Clinic in 1995, the technique represents the most accurate non-invasive method for the detection and staging of liver fibrosis and is currently performed in more than 100 centers worldwide. In this general review, the mechanical properties of soft tissues, principles of MRE, clinical applications of MRE in the liver and beyond, and limitations and future directions of this discipline -are discussed. Selected diagrams and images are provided for illustration.

Perfusion computed tomography of intracranial meningiomas: Invivo correlation of cerebral blood volume and vascular permeability.

A noninvasive method to predict the grade of a meningioma would be desirable since it would anticipate information about tumour nature, recurrence and improve tumour management and outcomes. The aim of the present study was to assess the ability of perfusion computed tomography (PCT) technique in predicting the meningioma grade before surgery. Data from PCT, such as cerebral blood volume (CBV) and permeability surface (PS), were correlated with immunohistolopathological information. Twenty-three patients with a diagnosis of intracranial meningioma underwent PCT for pre-surgical evaluation of CBV and PS. During surgery, samples from the centre and periphery of the tumour were obtained. Two correspondent regions of interest (ROIs) were drawn on CBV and PS maps. Central and peripheral CBV and PS mean values were calculated. PCT parameters were correlated to CD-34 and endoglin. There was a positive correlation between PS and CD-34. No correlation was found between PS values and endoglin, CBV values and CD-34 and endoglin values. Our findings suggest that PCT may support conventional morphological imaging in predicting meningioma grading before surgery.

Triple-echo steady-stateT2relaxometry of the human brain at high to ultra-high fields

Quantitative MRI techniques, such as T2 relaxometry, have demonstrated the potential to detect changes in the tissue microstructure of the human brain with higher specificity to the underlying pathology than in conventional morphological imaging. At high to ultra-high field strengths, quantitative MR-based tissue characterization benefits from the higher signal-to-noise ratio traded for either improved resolution or reduced scan time, but is impaired by severe static (B0 ) and transmit (B1 ) field heterogeneities. The objective of this study was to derive a robust relaxometry technique for fast T2 mapping of the human brain at high to ultra-high fields, which is highly insensitive to B0 and B1 field variations. The proposed method relies on a recently presented three-dimensional (3D) triple-echo steady-state (TESS) imaging approach that has proven to be suitable for fast intrinsically B1 -insensitive T2 relaxometry of rigid targets. In this work, 3D TESS imaging is adapted for rapid high- to ultra-high-field two-dimensional (2D) acquisitions. The achieved short scan times of 2D TESS measurements reduce motion sensitivity and make TESS-based T2 quantification feasible in the brain. After validation in vitro and in vivo at 3 T, T2 maps of the human brain were obtained at 7 and 9.4 T. Excellent agreement between TESS-based T2 measurements and reference single-echo spin-echo data was found in vitro and in vivo at 3 T, and T2 relaxometry based on TESS imaging was proven to be feasible and reliable in the human brain at 7 and 9.4 T. Although prominent B0 and B1 field variations occur at ultra-high fields, the T2 maps obtained show no B0 - or B1 -related degradations. In conclusion, as a result of the observed robustness, TESS T2 may emerge as a valuable measure for the early diagnosis and progression monitoring of brain diseases in high-resolution 2D acquisitions at high to ultra-high fields.

Clinical value of [18F]FDG-PET/CT in the detection of metastatic medullary thyroid cancer

PurposeTo evaluate the value of fluorine-18 2-deoxy-2-d-glucose positron emission tomography/computed tomography ([18F]FDG-PET/CT) in the detection of metastatic medullary thyroid cancer. MethodsFrom November 2006 to November 2012, 50 medullary thyroid cancer patients (median age 48.7years, range 18–76) who had a total thyroidectomy operation underwent whole-body [18F]FDG-PET/CT scans. The diagnostic accuracy of [18F]FDG-PET/CT was determined through both lesion-based and patient-based analyses. Further pathological tests were performed on all identified lesions or clinically followed for a minimum period of 6months. ResultsOne hundred forty-four suspicious lesions were identified by organ-based analysis. Of these lesions, [18F]FDG-PET/CT detected 99 true-positive lesions, sensitivity was 73.3%, and specificity was 66.7%. On the patient-based analysis, the overall sensitivity and specificity were calculated as 65.7% and 92.3%, respectively. Using a cutoff calcitonin value of 1000pg/ml, in patients with calcitonin lower than this value, sensitivity and specificity were 42.9% and 91.0%, respectively. In patients with calcitonin exceeding this value, they raised to 77.3% (χ2=4.392, P<.05) and 100% (χ2=0.197, P>.05), respectively. Compared with conventional imaging modality, PET/CT scans detected more lesions in 10 patients (20.4%) and correctly changed the treatment in 8 patients (16.3%). Conclusion[18F]FDG-PET/CT has excellent sensitivity and specificity, especially when the calcitonin value is higher than 1000pg/ml for detecting metastatic medullary thyroid cancer. Compared to conventional morphologic imaging methods, it provides additional information for diagnosis.

Depicting Medullary Thyroid Cancer Recurrence: The Past and the Future of Nuclear Medicine Imaging

Context:Inherited and sporadic medullary thyroid cancer (MTC) is an uncommon and medically challenging malignancy. Even if the extent of initial surgery is deemed adequate, the recurrence rate remains high, up to 50% in most series. Measurement of serum calcitonin is important in the follow-up of patients with MTC, and reliably reflects the existence of the disease.Evidence Acquisition:There is no single sensitive diagnostic imaging method to reveal all MTC recurrences or metastases. Conventional morphologic imaging methods (U/S, CT, and MRI) and several methods of nuclear medicine have been used for this purpose with variable accuracy.Results:The main role of nuclear medicine imaging is the detection of residual or recurrent tumor in the postoperative follow-up. In this review we present the radiopharmaceuticals used in the diagnosis of MTC recurrence, and comparison among them.Conclusions:The most used radiopharmaceuticals labelled with γ emitters are: Metaiodobenzylguanidine (MIBG), labelled with 131I or 123I, 111In-pentetreotide (Octreoscan), 99mTc-pentavalent dimercaptosuccinic acid (99mTc(V)-DMSA), and 99mTc-EDDA/HYNIC-Tyr3-Octreotide ( Tektrotyd). The radiopharmaceuticals labelled with a positron-emitting radionuclide (β+), suitable for positron emission tomography (PET) imaging are: 18F-fluorodeoxyglucose (18F-FDG), 18F-fluorodihydroxyphenylalanine (18F-DOPA), and 68Ga-labelled somatostatin analogues (68Ga-DOTATATE or DOTATOC).

Discrepancies and priorities in staging and restaging malignant lymphoma by SPET, SPET/CT, PET/CT and PET/MRI.

Due to the rapid development of modern imaging methods and also of medical oncology, there has been a significant progress in diagnosis and treatment of malignant lymphomas in the last few years. Nuclear medicine (NM) imaging methods gained new perspectives via the so called hybrid technologies-single-photon emission tomography combined with computed tomography (SPET/CT), positron emission tomography combined with computed tomography (PET/CT) and recently even positron emission tomography combined with magnetic resonance imaging (PET/MRI), which have led to a better image quality and diagnostic findings. Since SPET/CT evolved later than the "gold standard" 18F-FDG-PET/CT in lymphoma diagnostics, there are fewer studies with it, but it seems to be an excellent alternative to PET/CT. The role of PET/CT is confirmed up-to-date for typically 18F-FDG-avid lymphomas, in staging and restaging diffuse large B-cell and some aggressive follicular lymphomas, in a suspected relapse of treatment of both Hodgkin's and non-Hodgkin's lymphomas. There are many discussions about the "interim-PET" but the recent results indicate its important prognostic role for predicting disease-free survival and the possibility to modify treatment intensity in order to reduce late side effects. On the other hand, the routine and approbated use of conventional morphologic imaging methods CT and MRI serve as a "reference standard" for the newer hybrid technologies not only in diagnostics but also in the cost-benefit ratio analysis and remain the basic imaging modalities when hybrid methods are not available. In conclusion, our review points at the main advantages and disadvantages of each NM method mentioned above in the diagnosis and follow-up of malignant lymphomas. Specifically, problems in differential diagnostics and further possibilities to better optimize the diagnostic and therapeutic algorithm are mentioned.

Contrast-enhanced US quantitatively detects changes of tumor perfusion in a murine breast cancer model during adriamycin chemotherapy

Currently used morphologic criteria have limitations in assessing tumor response to chemotherapy because of the relatively slow tumor shrinkage as measured by conventional morphologic imaging. Functional imaging techniques show promising results in early assessment of tumor response to treatment. To quantitatively detect changes in tumor perfusion during chemotherapy with contrast-enhanced ultrasound. Twenty-three MCF-7 breast cancer bearing nude mice treated by either adriamycin (n = 11) or sterile saline (n = 12) were imaged before and after treatment with an ultrasound scanner after bolus injection of SonoVue. Regions of interest within the tumor were analyzed offline to determine perfusion parameters including peak enhancement (PE), area under the curve of wash-in (WiAUC), rise time (RT), wash-in rate (WiR), wash-in perfusion index (WiPI), and quality of fit (QOF). Hematoxylin and eosin was used to assess tumor cell density and immunohistochemical analysis was performed for evaluation of microvascular density (MVD). Treatment with adriamycin significantly reduced tumor growth in comparison to the control group (P < 0.001). There was no significant difference in perfusion parameters before treatment. Treatment with adriamycin resulted in a significant decrease in PE, WiAUC, WiR, and WiPI in comparison with control group (P < 0.01). The tumor cell density estimated by pathology slice was significantly lower in treated tumors than in control tumors after treatment (P < 0.001). Immunohistochemistry showed significant decreases of MVD in treated tumors as compared with control tumors (P < 0.001) after treatment. Quantitative contrast-enhanced ultrasound can detect the change of tumor perfusion after chemotherapy, which may enable early assess tumor response to chemotherapy.

Usefulness of Traditional Serum Biomarkers for Management of Breast Cancer Patients

The measurement of serum tumor markers levels in breast cancer (BC) patients is an economic and noninvasive diagnostic assay frequently requested by clinical oncologists to get information about the presence or absence of disease as well as its evolution. Despite their wide use in clinical practice, there is still an intense debate between scientific organizations about the real usefulness for patient monitoring during followup as well as response to therapy evaluation in case of advanced BC. In this review, we want to highlight the current recommendations published by scientific organizations about the use of “established” BC serum markers (CEA, TPA, TPS, CIFRA-21, CA15-3, and s-HER2) in clinical oncology practice. Moreover, we will focus on recent papers evidencing the usefulness of tumor markers levels measurement as a guide for the prescription and diagnostic integration of molecular imaging exams such as those performed by hybrid 18-fluorofeoxyglucose-positron emission tomography with integrated computed tomography. This technology is nowadays able to detect early cancer lesions undetectable by conventional morphological imaging investigation and most likely responsible for increasing of serum tumor markers levels.

Differentiation of an Intrapancreatic Accessory Spleen from a Small (&lt;3-cm) Solid Pancreatic Tumor: Value of Diffusion-weighted MR Imaging

To evaluate the value of diffusion-weighted (DW) imaging in differentiation of an intrapancreatic accessory spleen (IPAS) from a small (<3 cm) solid pancreatic tumor. This retrospective study was approved by the institutional review board, and informed consent was waived. Twenty patients with IPAS and 22 patients with small solid pancreatic tumors were included. All patients underwent abdominal magnetic resonance (MR) imaging with DW and gadoxetic acid-enhanced imaging. Qualitative (signal intensity) and quantitative (signal intensity and apparent diffusion coefficient [ADC]) evaluations were performed by two observers. Fisher exact test and Mann-Whitney U test were used for comparing groups. Compared with the spleen, the IPAS showed isointensity more frequently than did small pancreatic tumors on T2-weighted images (95% [19 of 20] vs 41% [nine of 22]), arterial phase images (100% [20 of 20] vs 18% [four of 22]), portal phase images (100% [20 of 20] vs 23% [five of 22]), late phase images (100% [20 of 20] vs 41% [nine of 22]), and DW images with b value of 0 sec/mm(2) (100% [20 of 20] vs 9% [two of 22]), b value of 100 sec/mm(2) (95% [19 of 20] vs 27% [six of 22]), and b value of 800 sec/mm(2) (100% [20 of 20] vs 27% [six of 22]), with significant differences (P < .01). The means of the absolute value of relative signal intensity and ADC ratio on DW images of IPAS were significantly lower and closer to zero than those of pancreatic tumors (P < .05). Visual assessment of the similarity between pancreatic lesion and spleen on DW images for diagnosis of IPAS yielded diagnostic accuracy, sensitivity, specificity, positive predictive value, and negative predictive value of 95% (40 of 42), 100% (20 of 20), 91% (20 of 22), 91% (20 of 22), and 100% (20 of 20), respectively, for observer 1 and 90% (38 of 42), 95% (19 of 20), 86% (19 of 22), 86% (19 of 22), and 95% (19of 20), respectively, for observer 2. In addition to conventional morphologic MR imaging, DW imaging can be used as a tool for differentiating IPAS from solid pancreatic tumors. http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.12112765/-/DC1.