Clinical Focus

  • Diagnostic Radiology

Academic Appointments

  • Clinical Associate Professor, Radiology

Professional Education

  • Residency: Indiana University Medical Center (1997) IN
  • Residency: Indiana University Medical Center (1994) IN
  • Fellowship: Stanford University Advanced Cardiovascular Imaging Fellowship (2005) CA
  • Board Certification: American Board of Radiology, Diagnostic Radiology (1997)
  • Medical Education: Indiana University School of Medicine (1993) IN
  • Post-Doctoral Fellow, Stanford University Medical Center, Cardiovascular Imaging (2005)
  • Resident, Indiana University / Methodist Hospital of Indiana, Diagnostic radiology (1997)
  • MD, Indiana University School of Medicine, Medicine (1993)

All Publications

  • Limited Aortic Intimal Tears: CT Imaging Features and Clinical Characteristics. Radiology. Cardiothoracic imaging Madani, M. H., Turner, V. L., Hallett, R. L., Willemink, M. J., Murillo, H., Chin, A. S., Berry, G. J., Fleischmann, D. 2022; 4 (6): e220155


    Limited aortic intimal tear is an uncommon lesion of the dissection spectrum. The lesion has several imaging features that are not well known, including asymmetric aortic contour abnormalities, filling defects, and various morphologic patterns, such as linear, L-shaped, T-shaped, and stellate configurations. Hemorrhage of the aortic wall may also be present in patients with this rare entity. This imaging essay reviews the CT imaging findings and clinical characteristics of patients with limited intimal tears. Keywords: Aorta, CT © RSNA, 2022.

    View details for DOI 10.1148/ryct.220155

    View details for PubMedID 36601454

    View details for PubMedCentralID PMC9806729

  • Delivery of hepatocyte growth factor mRNA from nanofibrillar scaffolds in a pig model of peripheral arterial disease. Regenerative medicine S Zaitseva, T., Yang, G., Dionyssiou, D., Zamani, M., Sawamura, S., Yakubov, E., Ferguson, J., Hallett, R. L., Fleischmann, D., Paukshto, M. V., Huang, N. F. 2020


    Background: Chemical modification of mRNA (mmRNA) substantially improves their stability and translational efficiency within cells. Nanofibrillar collagen scaffolds were previously shown to enable the spatially localized delivery and temporally controlled release of mmRNA encoding HGF both in vitro and in vivo. Materials &methods: Herein we developed an improved slow-releasing HGF mmRNA scaffold and tested its therapeutic efficacy in a porcine model of peripheral arterial disease. Results & conclusion: The HGF mmRNA wasreleased from scaffolds in a temporally controlled fashion in vitro with preserved transfection activity. The mmRNA scaffolds improved vascular regeneration when sutured to the ligated porcine femoral artery. These studies validate the therapeutic potential of HGF mmRNA delivery from nanofibrillar scaffolds for treatment of peripheral arterial disease.

    View details for DOI 10.2217/rme-2020-0023

    View details for PubMedID 32772903

  • Epidemiology and contemporary management of abdominal aortic aneurysms ABDOMINAL RADIOLOGY Ullery, B. W., Hallett, R. L., Fleischmann, D. 2018; 43 (5): 1032–43


    Abdominal aortic aneurysm (AAA) is most commonly defined as a maximal diameter of the abdominal aorta in excess of 3 cm in either anterior-posterior or transverse planes or, alternatively, as a focal dilation ≥ 1.5 times the diameter of the normal adjacent arterial segment. Risk factors for the development of AAA include age > 60, tobacco use, male gender, Caucasian race, and family history of AAA. Aneurysm growth and rupture risk appear to be associated with persistent tobacco use, female gender, and chronic pulmonary disease. The majority of AAAs are asymptomatic and detected incidentally on various imaging studies, including abdominal ultrasound, and computed tomographic angiography. Symptoms associated with AAA may include abdominal or back pain, thromboembolization, atheroembolization, aortic rupture, or development of an arteriovenous or aortoenteric fistula. The Screening Abdominal Aortic Aneurysms Efficiently (SAAAVE) Act provides coverage for a one-time screening abdominal ultrasound at age 65 for men who have smoked at least 100 cigarettes and women who have family history of AAA disease. Medical management is recommended for asymptomatic patients with AAAs < 5 cm in diameter and focuses on modifiable risk factors, including smoking cessation and blood pressure control. Primary indications for intervention in patients with AAA include development of symptoms, rupture, rapid aneurysm growth (> 5 mm/6 months), or presence of a fusiform aneurysm with maximum diameter of 5.5 cm or greater. Intervention for AAA includes conventional open surgical repair and endovascular aortic stent graft repair.

    View details for PubMedID 29313113

  • Abdominal aortic aneurysms: pre- and post-procedural imaging. Abdominal radiology (New York) Hallett, R. L., Ullery, B. W., Fleischmann, D. 2018


    Abdominal aortic aneurysm (AAA) is a relatively common, potentially life-threatening disorder. Rupture of AAA is potentially catastrophic with high mortality. Intervention for AAA is indicated when the aneurysm reaches 5.0-5.5cm or more, when symptomatic, or when increasing in size >10mm/year. AAA can be accurately assessed by cross-sectional imaging including computed tomography angiography and magnetic resonance angiography. Current options for intervention in AAA patients include open surgery and endovascular aneurysm repair (EVAR), with EVAR becoming more prevalent over time. Cross-sectional imaging plays a crucial role in AAA surveillance, pre-procedural assessment, and post-EVAR management. This paper will discuss the current role of imaging in the assessment of AAA patients prior to intervention, in evaluation of procedural complications, and in long-term follow-up of EVAR patients.

    View details for PubMedID 29460048

  • Pulmonary artery dissection complicating aortic dissection in a patient with bicuspid aortic valve and aortic coarctation. Radiology case reports Khaja, M. S., Hallett, R. L. 2017; 12 (3): 472-474


    We report a case of a type A aortic dissection with extension into the main pulmonary artery through a sinus of Valsalva fistula. Echocardiography and computed tomographic angiography of the chest were performed and bicuspid aortic valve, hemopericardium, and dilatation of the aortic root were found. A Stanford type A dissection was seen, extending to the distal transverse thoracic aorta, and there was a communication between the dissection at the left sinus of Valsalva and the main pulmonary artery, where a dissection flap was detected at computed tomographic angiography. This case report reviews the rare diagnosis of pulmonary artery dissection, multimodality imaging findings, and a brief review of etiology and management.

    View details for DOI 10.1016/j.radcr.2017.05.004

    View details for PubMedID 28828104

    View details for PubMedCentralID PMC5552015

  • Computed Tomography Angiography A Review and Technical Update RADIOLOGIC CLINICS OF NORTH AMERICA Fleischmann, D., Chin, A. S., Molvin, L., Wang, J., Hallett, R. 2016; 54 (1): 1-?


    The principles of computed tomography angiography (CTA) remain the following with modern-day computed tomography (CT): high-resolution volumetric CT data acquisition, imaging at maximum contrast medium enhancement, and subsequent angiographic two- and three-dimensional visualization. One prerequisite for adapting CTA to ever evolving CT technology is understanding the principle rules of contrast medium enhancement. Four key rules of early arterial contrast dynamics can help one understand the relationship between intravenously injected contrast medium and the resulting time-dependent arterial enhancement. The technical evolution of CT has continued with many benefits for CT angiography. Well-informed adaptations of CTA principles allow for leveraging of these innovations for the benefit of patients with cardiovascular diseases.

    View details for DOI 10.1016/j.rcl.2015.09.002

    View details for Web of Science ID 000367215000002

    View details for PubMedID 26654388

  • Contrast Medium Injection Technique MULTIDETECTOR-ROW CT OF THE THORAX, 2ND EDITION Fleischmann, D., Hallett, R. L., Schoepf, U. J., Meinel, F. G. 2016: 37–57
  • CT patterns of fungal pulmonary infections of the lung: Comparison of standard-dose and simulated low-dose CT EUROPEAN JOURNAL OF RADIOLOGY Christe, A., Lin, M. C., Yen, A. C., Hallett, R. L., Roychoudhury, K., Schmitzberger, F., Fleischmann, D., Leung, A. N., Rubin, G. D., Vock, P., Roos, J. E. 2012; 81 (10): 2860-2866


    To assess the effect of radiation dose reduction on the appearance and visual quantification of specific CT patterns of fungal infection in immuno-compromised patients.Raw data of thoracic CT scans (64 × 0.75 mm, 120 kVp, 300 reference mAs) from 41 consecutive patients with clinical suspicion of pulmonary fungal infection were collected. In 32 patients fungal infection could be proven (median age of 55.5 years, range 35-83). A total of 267 cuboids showing CT patterns of fungal infection and 27 cubes having no disease were reconstructed at the original and 6 simulated tube currents of 100, 40, 30, 20, 10, and 5 reference mAs. Eight specific fungal CT patterns were analyzed by three radiologists: 76 ground glass opacities, 42 ground glass nodules, 51 mixed, part solid, part ground glass nodules, 36 solid nodules, 5 lobulated nodules, 6 spiculated nodules, 14 cavitary nodules, and 37 foci of air-space disease. The standard of reference was a consensus subjective interpretation by experts whom were not readers in the study.The mean sensitivity and standard deviation for detecting pathological cuboids/disease using standard dose CT was 0.91 ± 0.07. Decreasing dose did not affect sensitivity significantly until the lowest dose level of 5 mAs (0.87 ± 0.10, p=0.012). Nodular pattern discrimination was impaired below the dose level of 30 reference mAs: specificity for fungal 'mixed nodules' decreased significantly at 20, 10 and 5 reference mAs (p<0.05). At lower dose levels, classification drifted from 'solid' to 'mixed nodule', although no lesion was missed.Our simulation data suggest that tube current levels can be reduced from 300 to 30 reference mAs without impairing the diagnostic information of specific CT patterns of pulmonary fungal infections.

    View details for DOI 10.1016/j.ejrad.2011.06.059

    View details for Web of Science ID 000308079700067

    View details for PubMedID 21835569

  • CT Screening and Follow-Up of Lung Nodules: Effects of Tube Current-Time Setting and Nodule Size and Density on Detectability and of Tube Current-Time Setting on Apparent Size AMERICAN JOURNAL OF ROENTGENOLOGY Christe, A., Torrente, J. C., Lin, M., Yen, A., Hallett, R., Roychoudhury, K., Schmitzberger, F., Vock, P., Roos, J. 2011; 197 (3): 623-630


    The purpose of the study was to quantify and compare the effect of CT dose and of size and density of nodules on the detectability of lung nodules and to quantify the influence of CT dose on the size of the nodules.From 50 patients a total of 125 cuboidal regions of interest (3 × 3 × 1.5 cm volumes) showing a single nodule (≤ 8 mm) and 27 normal cuboids were selected. Image sets were reconstructed with the software from raw data simulating different dose levels: 300 (original dose), 220, 180, 140, 100, 80, 60, 50, 40, 30, 20, 10, and 5 reference mAs. A logistic regression model was used to analyze detectability for three blinded readers. Odds ratios were calculated for nodule size smaller than 3 mm versus 3 mm and larger and for nodule attenuation of -300 HU and greater versus less than -300 HU.Tube current-time settings of 10 mAs and greater were not associated with a significant difference in individual reader sensitivity compared with the standard setting of 300 mAs. At 5 mAs only one reader had a significant decrease in sensitivity, from 82% to 77% (p = 0.0035). According to the odds ratios and logistic regression results, the strongest negative effect on sensitivity can be assumed for low nodule density followed by small nodule size and dose level. The mean nodule volume measurement error between 5 and 300 mAs was 2.2% ± 18% (SD) and much lower than the interobserver volume measurement error rate of 38% ± 45%.The results show the feasibility of a low-dose CT protocol at 10 mAs for follow-up of lung nodules. Computer-aided volume measurement in follow-up of lung nodules decreases interobserver variability.

    View details for DOI 10.2214/AJR.10.5288

    View details for Web of Science ID 000294165600046

    View details for PubMedID 21862804

  • MR Imaging of Parotid Tumors: Typical Lesion Characteristics in MR Imaging Improve Discrimination between Benign and Malignant Disease AMERICAN JOURNAL OF NEURORADIOLOGY Christe, A., Waldherr, C., Hallett, R., Zbaeren, P., Thoeny, H. 2011; 32 (7): 1202-1207


    The surgical approach to parotid tumors is different for benign and malignant neoplasms, but the clinical symptoms do not correlate well with histology. Difficulties in tumor classification also arise in imaging modalities, in which sonography has the lowest and MR imaging, the highest accuracy. The purpose of this study was to review our experience using conventional MR imaging of the neck in the evaluation of parotid tumors and to evaluate which MR imaging findings are best able to predict malignant histology.Eighty-four consecutive patients (43 males, 41 females; median age, 56 years; range, 9-85 years) with parotid gland tumors who underwent MR imaging before surgery were prospectively included in the present study and retrospectively analyzed. Histology was available for all tumors. We analyzed the following MR imaging parameters: signal intensity, contrast enhancement, lesion margins (well-defined versus ill-defined), lesion location (deep/superficial lobe), growth pattern (focal, multifocal, or diffuse), and extension into neighboring structures, perineural spread, and lymphadenopathy.The 57 (68%) benign and 27 (32%) malignant tumors consisted of 29 pleomorphic adenomas, 17 Warthin tumors, 11 various benign tumors, 5 mucoepidermoid carcinomas, 3 adenoid cystic carcinomas, 1 acinic cell carcinoma, 1 carcinoma ex pleomorphic adenoma, 9 metastases, and 8 various malignant neoplasms. Specific signs predictive of malignancy were the following: T2 hypointensity of the parotid tumor (P = .048), ill-defined margins (P = .001), diffuse growth (P = .012), infiltration of subcutaneous tissue (P = .0034), and lymphadenopathy (P = .012).Low signal intensity on T2-weighted images and postcontrast ill-defined margins of a parotid tumor are highly suggestive of malignancy.

    View details for DOI 10.3174/ajnr.A2520

    View details for Web of Science ID 000294275100010

    View details for PubMedID 21724574

  • Tools of the trade for CTA: MDCT scanners and contrast medium injection protocols. Techniques in vascular and interventional radiology Hallett, R. L., Fleischmann, D. 2006; 9 (4): 134-142


    The introduction of multi-detector row computed tomography (MDCT) scanners in 1998 ushered in new advances in CT angiography (CTA). The subsequent expansion of MDCT scanner capabilities, coupled with advances in understanding of contrast medium (CM) dynamics, has further improved the clinical availability and consistency of CTA. We will review recent advances in CT scanner technology and discuss early CM dynamics. Specifically, we describe an approach tailored to the available scanner technology and to patient size aimed at providing consistently robust CTA studies across all vascular territories. A rational method to design combined CTA scan/injection protocols to facilitate this goal will be described. Our current experience with a simplified protocol for CTA with 64-MDCT will also be explained.

    View details for PubMedID 17709077

  • In vivo MR angiographic quantification of axial and twisting deformations of the superficial femoral artery resulting from maximum hip and knee flexion JOURNAL OF VASCULAR AND INTERVENTIONAL RADIOLOGY Cheng, C. P., Wilson, N. M., Hallett, R. L., Herfkens, R. J., Taylor, C. A. 2006; 17 (6): 979-987


    The goal of this study was to quantify in vivo deformations of the superficial femoral artery (SFA) during maximum knee and hip flexion with use of magnetic resonance (MR) angiography to improve description of the complex, dynamic SFA environment.Contrast medium-enhanced MR angiography was performed on the leg vasculature of eight healthy adults in the supine and fetal positions. The SFA was defined as the centerline path of the iliofemoral segment from the profunda femoris to the descending genicular artery. Deformations that resulted from flexion from the supine position to the fetal position were quantified with the SFA path and its branches.Fourteen SFAs shortened from the supine position to fetal position, whereas two lengthened. Six of eight left SFAs twisted counterclockwise, and seven of eight right SFAs twisted clockwise. Straightness percentages for supine and fetal SFAs were 99.1%+/-0.4% and 98.7%+/-0.6%, respectively. From the supine position to the fetal position, the SFA shortened 13%+/-11% (P<.001) and twisted 60 degrees+/-34 degrees (P<.001). SFA arc length and percent shortening were strongly correlated (r>.8) between left and right limbs; however, no significant correlation existed for SFA twist angle.Complex and varying vascular and muscular anatomy among study participants made SFA lengths and deformations from the supine position to the fetal position unpredictable a priori; however, there were strong symmetries between left and right SFAs in terms of arc length, length change, and direction of twist. The data show that, from the supine position to the fetal position, the SFA tended to shorten and twist substantially, suggesting these as possible fracture mechanisms and also providing important parameters for stent design.

    View details for DOI 10.1097/01.RVI.0000220367.62137.E8

    View details for Web of Science ID 000238334500006

    View details for PubMedID 16778231

  • CT angiography of peripheral arterial disease JOURNAL OF VASCULAR AND INTERVENTIONAL RADIOLOGY Fleischmann, D., Hallett, R. L., Rubin, G. D. 2006; 17 (1): 3-26


    Lower-extremity computed tomographic (CT) angiography (ie, peripheral CT angiography) is increasingly used to evaluate patients with peripheral arterial disease. It is therefore increasingly important for all vascular specialists to become familiar with the strengths and limitations of this new technique. The aims of this review are to explain the principles of scanning and injection technique for a wide range of CT scanners, to explain and illustrate the properties of current image postprocessing tools for effective visualization and treatment planning, and to provide an overview of current clinical applications of peripheral CT angiography.

    View details for DOI 10.1097/01.RVI.0000191361.02857.DE

    View details for Web of Science ID 000236517800002

    View details for PubMedID 16415129