About Us

Dr. Abraham D. Knoll, MD is an endovascular specialist with fellowship training in Vascular and Interventional Radiology at New York University Langone Medical Center. He brings a unique blend of clinical expertise, academic achievement, entrepreneurial leadership, and community service to his work in medicine. 

After earning his medical degree from the NYU School of Medicine, Dr. Knoll pursued advanced training at Columbia University Medical Center/Harlem Hospital Center, where he completed his residency in Diagnostic Radiology and was selected as Chief Resident. He then went on to complete fellowship training at NYU Langone, focusing on minimally invasive, image-guided procedures that provide cutting-edge vascular treatment options with less risk and faster recovery for patients. 

Throughout his career, Dr. Knoll has balanced clinical practice with innovation. As the Founder and Chief Medical Officer of Mobile Vascular Physicians, he helped design and lead a novel model of mobile vascular care, bringing advanced diagnostics and treatment directly into communities. His leadership shaped the company’s growth and strengthened patient access to specialized vascular services, enhancing patient-centered care. 

Dr. Knoll’s academic work has been widely recognized. He has authored peer-reviewed publications on topics ranging from radiation-induced lung injury to advanced interventional techniques and has presented nationally and internationally, including at meetings of the Radiological Society of North America (RSNA), the Society of Interventional Radiology (SIR), and the International Symposium on Endovascular Therapy (ISET). His contributions to the field were honored with the RSNA Roentgen Resident/Fellow Research Award. Beyond medicine, Dr. Knoll has long been active in education, mentorship, and community service. He has co-founded charitable organizations, served as a volunteer in both local and international initiatives, coached youth sports, and mentored pre-medical students. Licensed to practice medicine in New York, New Jersey, Pennsylvania, Florida, Ohio, Texas, and California, Dr. Knoll continues to merge his clinical expertise with a vision for accessible, patient-centered care. Whether in the clinic, research lab, or community, his work reflects a consistent commitment to improving health outcomes and expanding the reach of modern medicine.

Dr. Daniel Portal is a board-certified, fellowship-trained vascular and interventional radiologist who combines advanced clinical expertise with strong academic and operational leadership. He delivers precise, patient-centered care across a wide range of imaging and minimally invasive, image-guided treatments.

Dr. Portal earned his medical degree from Stony Brook University School of Medicine. He completed a preliminary internship in Internal Medicine at Maimonides Medical Center, followed by residency training in Diagnostic Radiology at Northwell Health Staten Island University Hospital. He then pursued advanced fellowship training in Vascular and Interventional Radiology at Memorial Sloan Kettering Cancer Center and NewYork-Presbyterian Weill Cornell Medical Center, where he gained extensive experience in complex vascular and oncologic interventions.

Throughout his career, Dr. Portal has held both attending and leadership roles at multiple institutions. As Chief of Interventional Radiology at Wyckoff Heights Medical Center in Brooklyn, he built and expanded the department into a cutting-edge, full-service Interventional Radiology program, improving access to minimally invasive therapies and elevating the level of care available to the community. His clinical work focuses on treatments designed to minimize risk, reduce recovery time, and optimize outcomes for patients.

Dr. Portal is actively engaged in academic medicine and has presented at multiple national Interventional Radiology conferences, sharing clinical expertise and advances in minimally invasive techniques with peers nationwide. In addition to his interventional practice, he maintains an active diagnostic radiology practice and provides teleradiology services, bringing a comprehensive and detail-oriented perspective to every case.

Known for his thoughtful approach and clear communication, Dr. Portal is committed to helping patients fully understand their diagnoses and treatment options. Whether performing advanced procedures or interpreting complex imaging studies, his work reflects a consistent commitment to clinical excellence, safety, and compassionate care.

Alyssa Stevenson is a New Jersey native with extensive experience supporting the growth and delivery of advanced vascular and embolization services.

Prior to joining VivaVein, she worked closely with Dr. Abe Knoll at Mobile Vascular Physicians, where she helped support the growth of a pioneering mobile vascular care model. Through this work, Alyssa developed extensive experience across the vascular and embolization space, collaborating with interventional radiologists and referring clinicians to expand access to minimally invasive, image-guided treatments.

At VivaVein, Alyssa leads business development, physician relations, and patient outreach efforts- strengthening referral partnerships, supporting clinical collaboration, and ensuring a seamless, white-glove care experience from first contact through treatment.