Meet our Team of Talented Specialists


Dr. Jill Williamson, Board-Certified Emergency and Critical Care Specialist, Medical Director of Emergency and Specialty Services, and AIMSS Founder

After graduating from veterinary school in Iowa, Dr. Williamson headed to the west coast and has been in California ever since. She practiced in emergency and specialty hospitals in Northern California prior to starting her ACVECC residency in 2002. Dr. Williamson completed her residency in Emergency and Critical Care at the Pet Emergency and Specialty Center of East County in La Mesa, California.

Dr. Williamson puts her advanced skills in critical care to work when a pet’s condition becomes life threatening. After making an initial assessment, she stabilizes the patient, and then provides continuous support and monitoring based on patient needs. Life-saving therapy may require IV fluids, blood or plasma transfusions, mechanical ventilation, oxygen support, surgery, nutritional delivery, and pain control. Dr. Williamson delivers cutting-edge expertise with compassion and love.

“Critical care is the core of medicine; it requires intimate knowledge of physiology. Although deeply challenging on intellectual and emotional levels, critical care can be amazingly rewarding.”

Dr. Williamson spends her free time riding both road and mountain bikes, exploring the culinary scene of Northern California, and hiking.

Dr. Dorrie Black, Board-Certified Emergency and Critical Care Specialist

Dr. Black is a fifth generation Californian, raised in Danville. After completing both her DVM and MPVM degrees at UC Davis and her small animal internship in San Diego, she went east to train in the field of veterinary emergency and critical care medicine at the University of Pennsylvania in Philadelphia.

“I specialized in emergency and critical care medicine to be the best veterinarian I could be for critically ill dogs and cats. I love the variety and different things that we see every day. No one single day is ever the same. I love the collaboration with my fellow veterinarians at AIMSS and seeing my patients get better.”

Her special areas of interest include respiratory diseases, coagulation disorders, and antimicrobial therapy. Dr. Black is widely published and speaks frequently on topics in emergency and critical care.

Dr. Black is thrilled to be back home in Northern California. When she is not at the hospital, she enjoys the great outdoors, especially trail running and kayaking. Her furry companions, Chloe, Butter, and Freeway, are at her side during her many adventures.

Dr. Sophie Dennison, Board-Certified Radiologist and AIMSS Partner

Dr. Dennison performs ultrasound, radiography, CT, and MRI, providing noninvasive evaluations of the internal organs and allowing abnormalities to be identified and characterized. In many cases, the appropriate application of these scientific methods means that unnecessary surgery may be avoided.

Dr. Dennison states, “I love the hands-on approach of ultrasound services. I enjoy all aspects of diagnostic imaging and believe in employing state-of-the-art technology to achieve the most efficient and appropriate imaging for the accurate diagnosis of the individual patient.”

As Medical Director of Specialty Services, Dr. Dennison provides guidance, oversight, and quality assurance for patients under the care of the board-certified specialists at AIMSS. She promotes ongoing education of specialists to ensure that practices are based on the newest research and technology. She uses her broad range of expertise to work with the team of specialists to develop the appropriate treatment plan for optimal care.

A native of the UK, Dr. Dennison received her veterinary training at the University of Edinburgh. She completed her radiology residency at the University of Wisconsin School of Veterinary Medicine and achieved board certification in Small Animal Radiology in 2009.

Skilled in the diagnostic imaging of domestic, avian, and marine mammal species, she is widely published and consults locally, nationally, and internationally on cross-sectional imaging cases.

When not working, Dr. Dennison enjoys skiing, playing ice hockey, and hiking. She also loves watching British TV and hanging out with her two cavaliers, Brie and Devon.


Dr. Cheri Nielsen, Board Certified Small Animal Surgeon

Dr. Nielsen earned an undergraduate degree in biomedical engineering with a minor in applied mathematics. It wasn’t until her second year of medical school at the Johns Hopkins School of Medicine, when her own dog needed the services of a surgical specialist, that she became aware of veterinary surgery as a career option. This opened the door to a life-changing decision; she left Johns Hopkins to pursue a veterinary career. She earned her DVM degree at UC Davis while concurrently completing an MS degree in biomedical engineering then continued on to a one-year clinical internship at Colorado State University. She completed a three-year surgical residency at the University of Minnesota and successfully fulfilled the rigorous credentialing and examination requirements to become a Diplomate of the American College of Veterinary Surgeons in small animal surgery.

Dr. Nielsen has been providing innovative and compassionate specialty surgical care for bay area pets since 2006. She is skilled in a wide range of procedures and her surgical practice includes orthopedic, neurologic, soft tissue, and oncologic/reconstructive surgery. Patient comfort and client communication are top priorities for Dr. Nielsen, who has a particular passion for minimally invasive procedures, wound management, and cancer.


Dr. Katharine Andres, DVM, DACVIM/Oncology

Dr. Kathy Andres graduated from UC Davis School of Veterinary Medicine with honors and completed a small animal internship at the Animal Medical Center in New York City. After several years of family and emergency practice in the San Francisco Bay Area, Dr. Andres fulfilled her dream of becoming a veterinary oncologist through her residency in oncology at BAVS and achieving board certification in 2011. She has received numerous awards during her academic and clinical training acknowledging her gentle approach to pets and their families and her special interest in the field of oncology.

At work, Dr. Andres enjoys collaborating and learning from her veterinary colleagues. She develops long-term relationships with her clients and patients and loves to hear their stories while developing therapy plans that meet the needs of the family and of the patient.

Originally from the East Coast, Dr. Andres lives in her beloved San Francisco with her family including several dogs, a cat and multiple parrots. She enjoys being silly with kids, home remodeling, cooking and reading late into the night