Prospective Comparison of ICG Microangiography and Conventional Angiography in Severe Frostbite
Conditions: Frostbite
Sponsor: HealthPartners Institute

Study Name: Pilot Study: Prospective comparison of ICG microangiography and conventional 
angiography in severe frostbite 
Principal Investigator: Alexandra Lacey, MD 
Date Submitted: December 1, 2022 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

1. Summary 
Severe frostbite injury is a significant cause of morbidity in northern climates. Here in Minnesota, we 
have some of the highest numbers of severe frostbite injuries in North America 1. As a result, at 
Regions Hospital we have the best opportunity to study this disease process and improve outcomes 
for frostbite patients. The diagnostic methods for severe frostbite injury vary from institution to 
institution and there is no standard practice. Commonly utilized methods include conventional 
angiography, Technetium 99 triple phase bone scans, SPECT studies, Indocyanine Green 
microangiography, and doppler studies 1-4. 
 
Regions Hospital is one of the busiest institutions utilizing conventional angiography. Conventional 
angiography can fully delineate the vascular occlusion (cut off) found in severe frostbite patients in 
highly granular detail. However, this method of diagnosis is very labor intensive and not without risk 
(pseudoaneurysms, contrast induced nephropathy, complications associated with lying flat for up to 
72 hours, etc2,5-6). By contrast, Indocyanine Green (ICG) microangiography is a relatively low risk 
imaging modality that can be done at the bedside. This method shows the microvascular soft tissue 
perfusion and demonstrates where the tissue is ischemic in severe frostbite injury. ICG imaging 
involves delivering a small amount of ICG dye (5 mg) via peripheral IV and using a specialized camera 
that captures the dye fluorescing in infra-red light.7 This method of imaging is FDA approved and has 
been shown to be highly accurate at predicting final amputation level in severe frostbite injury 8.  
 
The proposed pilot study aims to directly compare conventional angiography imaging to ICG 
microangiography in adult patients with severe frostbite. Severe frostbite is defined as 4th degree: 
frostbite resulting in vascular occlusion and tissue ischemia. Both imaging modalities have been 
used for the diagnosis and monitoring of severe frostbite injury but there has never been a study 
directly comparing these two imaging modalities2,7-8. We will be obtaining consent from adult 
patients with severe frostbite injury who are undergoing intra-arterial thrombolysis. During their 
treatment, an angiography will be performed according to the Regions Hospital standard of care 
protocol, followed immediately by an ICG microangiography image. These two diagnostic images will 
be directly compared by a radiologist and a burn surgeon to determine the image concordance or 
discordance. We will also monitor patients for potential side effects or adverse reactions to the ICG 
imaging, but as stated above, the ICG microangiography is low-risk and we do not anticipate any 
adverse reactions related to this procedure. 
  
Pending the results of this study, we will pursue a full-scale version of this study, which will track 
patients in a longitudinal manner to determine the outcome of their frostbite treatments. The 
proposed pilot study is designed to assess feasibility, the degree of concordance or discordance 
between the two imaging modalities, and side effects of imaging.  
 
2. Study Aims 
Primary Outcome: Angiography and ICG microangiography imaging concordance/discordance. 

Research question: Does the vascular cut off on conventional angiography found in severe frostbite 
patients correlate with the tissue ischemia demonstrated on ICG microangiography in severe 
frostbite?    
Hypothesis: Conventional angiography can fully delineate the vascular occlusion (cut off) found in 
severe frostbite patients in highly granular detail. ICG microangiography shows the microvascular 
soft tissue perfusion and demonstrates where the tissue is ischemic in severe frostbite injury. We 
hypothesize that these two imaging modalities will be concordant at demonstrating the ischemic 
tissue present in severe frostbite.  
Secondary Outcome: Safety. 
Research question: Is indocyanine green safe when delivered in close association with contrast dye 
(used in conventional angiography)? 
 
Hypothesis: Contrast dye used in conventional angiography is associated with nephrotoxicity and 
other risks. Indocyanine green dye is generally considered to be a highly safe product with minimal 
risks associated with administration. It has been used for decades with minimal side effects. It is 
hypothesized that ICG dye will not result in any increase in risk to the patient when delivered in 
temporal proximity to conventional dye.  
 
3. Background, Rationale, Significance 
 
Frostbite injury has been a significant cause of morbidity and mortality for as long as humans have 
experienced cold winters. When frostbite occurs, there are two primary mechanisms through which 
tissue damage occurs, though the main mechanism we will focus on here is systemic cooling. Frostbite is 
a multiphase process that starts with systemic cooling. As the body cools, blood is shunted from the 
extremities to the core to maintain heat in the vital organs. During this shunting, there is extensive 
vasospasm in the extremities and the tissue becomes ischemic. Upon further cooling, tissue ice crystals 
form within the cells and interstitial spaces causing desiccation and cell destruction. This occurs in the 
soft tissues and also affects the endothelium of the micro- and macrovasculature. Clots form in the 
microvasculature, worsening the ischemia. All ischemic tissues release pro-inflammatory factors, which 
increase inflammation and worsen clotting. 9-14 
 
Upon rewarming of the frozen tissues, the reperfusion can worsen the inflammatory state as these 
factors released by the ischemic tissue are now able to circulate. Rapid rewarming is used as a tool to 
mitigate this reperfusion injury, but it does not eliminate the damage 1,15. After rapid rewarming, the 
tissue is assessed for the extent of damage to determine next treatment steps. Diagnosis varies by 
institution, but the main goal of all diagnostic modalities is to determine if there is a vascular cutoff 
causing tissue ischemia.  
 
At Regions Hospital, the main diagnostic method that has been used for over 20 years is conventional 
angiography. This clearly demonstrates the microvasculature of the tissues and allows the intra-arterial 
catheter directed sheaths to be placed to start thrombolytics, heparin, and vasodilators to treat the 
tissue ischemia 2. Other diagnostic modalities used elsewhere include Technetium 99 triple phase bone 

scans, SPECT imaging, and indocyanine green (ICG) microangiography 16. All of these imaging modalities 
demonstrate the perfusion of the affected tissue but do not allow for directed delivery of thrombolytics. 
In institutions that use these imaging techniques, thrombolytics are typically delivered in an intravenous 
fashion rather than intra-arterial.  
 
ICG microangiography is a technology that has had rapidly expanding applications in recent decades. 
These have included retinal imaging, determining perfusion of colorectal anastomoses, biliary imaging, 
and assessing the blood supply of tissue flaps 17-19. It has recently been used in diagnosis of frostbite with 
good correlation with severe final amputation levels. It is easy to use, non-radiating, can be performed 
at the bedside, and cheaper than other imaging modalities 7-8. 
 
Given that every hospital has different diagnostic and treatment algorithms, these different imaging 
modalities have rarely been compared in the same patient. The current best metric is comparing the 
imaging modality with the amount of tissue that is amputated as demonstrated in prior studies cited 
here. This research application provides a unique opportunity to compare two imaging modalities head-
to-head in the same patient and determine their concordance or discordance.  
 
 
4. Study Design 
This pilot study is an unblinded prospective interventional imaging study designed to determine whether 
ICG microangiography is as accurate as conventional angiography in determining the ischemic tissue 
present in severe frostbite.    
We will capture images of 10 patients who are undergoing conventional angiography and thrombolysis 
for severe frostbite. All patients will be adults (>18 years old) and able to provide consent for 
participation in the study. Once the patient has been started on thrombolysis, they will be evaluated for 
whether they meet the study’s inclusion/exclusion criteria, and then approached by a CCRC Clinical 
Research Coordinator about possible involvement in this research project. If they consent to the study, 
then the ICG microangiography imaging will be performed immediately following their next 
conventional angiography session. When a patient is undergoing catheter directed thrombolysis, they 
have conventional angiography sessions to assess progression every 24 hours for up to 72 hours. In this 
pilot study, we would administer the ICG microangiography following one of these sessions, after 
consent is obtained. This imaging would be performed in the IR suite immediately following the 
conventional angiography session.  
This study is quasi-experimental. The inclusion of a second (ICG) imaging technique is not a therapeutic 
modality and has limited risks to the study participants. ICG dye is very well tolerated and only 
contraindicated in iodine allergy. There is no radiation associated with this imaging study. Participants 
will serve as their own controls as they will be receiving both types of imaging.  
 
Population 
Patients will be identified by the burn surgeons and advance practice practitioners. They will evaluate 
the patients to determine whether they meet the inclusion/exclusion criteria of the study. 

 
a. Inclusion criteria 
1. Adult (>18 years old) patients 
2. Diagnosed with severe frostbite by conventional angiography 
3. Undergoing thrombolysis with catheter directed lytics 
4. Clinically sober at the time of consent 
5. Cognitively able to provide consent as determined by clinician’s best 
judgement 
6. Normal kidney function (GFR >60) 
 
b. Exclusion criteria 
1. Pregnant. Pregnancy will be determined by standard of care pregnancy test 
performed on all female frostbite patients who are receiving lytics.  
2. Iodine allergy. 
 
c. Sample size 
1. Ten ICG images will be performed on 10 unique patients who are already 
receiving conventional angiography as standard of care. 
2. Feasibility: Based on historical data from Regions Hospital between 2006-
present, there are typically 20-70 patients per winter who undergo 
conventional angiography and catheter directed lytics who would be 
candidates to participate in this study. We anticipate approaching 20 
patients to reach our target sample size of 10. 
 
Data collection process 
1. Process for identification of patients: All patients undergoing catheter 
directed thrombolysis for severe frostbite injury are managed primarily by 
the Burn Team. As such, the burn surgeons and burn advance practice 
practitioners will be able to identify patients who meet the inclusion criteria 
for this study.  
2. Recruitment: The burn surgeon will identify patients and confirm that they 
meet the inclusion/exclusion criteria for the study. They will inform the 
Clinical Research Coordinator from the Critical Care Research Center (CCRC), 
who will approach the patient about the study and obtain informed 
consent. 
3. Consent: Written consent will be obtained by the CCRC Clinical Research 
Coordinator who is the Lead Coordinator for this study (see attached ICF). 
Competency to provide consent will be confirmed by the coordinator 
obtaining consent by testing for comprehension after the consent 
conversation and before a signature is obtained.  
 
 
 

Data sources 
Data sources will include chart review, conventional angiography images, and ICG 
microangiography images. Images and data will be stored on an encrypted HealthPartners 
computer at Regions Hospital. 
Data acquisition 
• 
Data will be collected by Dr. Alexandra Lacey, burn surgeon. 
• 
Patient contact by study personnel will include consenting the patient for this study (CCRC 
Clinical Research Coordinator) and performance of the ICG microangiography study (performed 
by Dr. Alexandra Lacey). 
• 
Data points from the Electronic Medical Records will include: 
o MRNs 
o Last name, first name 
o Basic demographics: age, gender, race, ethnicity 
o Social: substance abuse, mental health diagnoses, housing status 
o Medical: comorbid conditions CAD/vascular disease, diabetes mellitus, renal 
insufficiency, smoking 
• 
Data from the conventional angiography include: 
o Medications currently being infused 
o Hours of treatment 
o Areas of poor perfusion as measured by the Hennepin Frostbite Score 20 (see attached 
score sheet) 
• 
Data from the ICG microangiography include: 
o Areas of poor perfusion as measured by the Hennepin Frostbite Score 
 
DATA DICTIONARY GOES HERE 
Statistical Analysis Plan 
The primary dependent variable in this study is the Hennepin Frostbite Score that will be generated 
from each imaging technique. We will compute a correlation between the Hennepin Frostbite Score 
produced by the conventional angiography and the Hennepin Frostbite Score produced by the ICG 
microangiography. While we predict a high correlation between the scores generated by the two 
methods, a high correlation does not necessarily imply that there is good agreement between the two 
methods. Thus, we will also use a Bland-Altman (difference) plot to analyze the agreement between the 
two imaging techniques. 
 
Power analysis or statement of precision  
This will be a small pilot study that will not be adequately powered to determine significance. 
 

5. Interventions and treatments 
As previously stated, the main intervention in this study is the performance of an ICG 
microangiography study immediately following a conventional angiography image in patients 
who are undergoing catheter directed thrombolysis for severe frostbite injury. This will be a 
one-time diagnostic measure with no additional follow up or imaging required. This is not a 
therapeutic intervention, but a secondary imaging study with minimal risk.  
 
6. Setting/Environment/Organizational feasibility 
 
Study participants will be patients who are being treated primarily on the Burn Unit at Regions Hospital. 
Consent will be obtained while they are inpatient by a CCRC Clinical Research Coordinator. The ICG 
microangiography imaging will be performed in the Interventional Radiology (IR) suite immediately 
following the patient’s conventional angiography imaging. This has been discussed with the IR 
leadership and they agree to performing this study in their space (see attached Letter of Support). Dr. 
Alexandra Lacey, burn surgeon, will be performing the ICG microangiography and staying in constant 
communication with the IR staff performing the conventional angiography imaging. Given the small 
number of images need for this pilot study, this method of communication and number of ICG providers 
will be adequate.  
 
7. Risks and Benefits 
ICG microangiography dye is very safe and well tolerated. It will be delivered via a peripheral IV, 
which the patient will already have in place per protocol for all patients with severe frostbite injury. The 
small 5mg dose used for this study has limited possible side effects. There is no radiation exposure for 
this imaging modality. The only known risk is allergic reaction to the ICG dye. Patients with a known 
iodine allergy will be excluded from this study due to possible reaction to the conventional angiography. 
All patients who participate in the study will be monitored following dye administration as standard of 
care for ICU level patients who have catheter directed lytics being delivered.  
Psychological, social, legal, and economic risks are not foreseeable for this study. There is no direct 
benefit to the patient from participating in this study.  
8. Strengths and Limitations 
Strengths of the study: this is the first study looking at ICG microangiography and conventional 
angiography in the same patients. Both techniques have been studied individually but this has 
never been examined in a head-to-head manner in frostbite. Pending the results of this study, 
this may help to determine what the true ‘gold standard’ should be for frostbite imaging.  
Limitations of the study: This will be a small pilot study that will not be adequately powered to 
determine significance. This is also a single institution study and is a single snapshot in time (not 
longitudinal). Concordance of imaging with long term outcomes will not be calculated as part of 
this preliminary study.  
 

9. Data Confidentiality and Privacy 
All data will be stored on the private HealthPartners computer of Dr. Alexandra Lacey. This 
computer and its contents are stored in a locked office in the Burn Unit and are not accessible to any 
other members of the research or healthcare teams. Any data that are extracted for analysis and/or 
publication will be de-identified. After completion of this pilot and any follow up studies, identifiable 
data will be destroyed by the PI. There is no plan to share these data with other entities.  
10. Timeline 
The goal timeline for this limited project is to begin winter 2022 (January 2022 – March 2023) to 
make sure we have enough patients to allow us to collect all 10 images for this study. Data analysis will 
be completed over the spring and summer to allow for the creation any necessary follow up project for 
the following winter.  
11. Dissemination of data 
Findings of scientific significance will be submitted for presentation at the American Burn 
Association annual meeting. The typical deadline for abstract submission is early October so all analyses 
will be completed by that time. Findings will also be written up for publication in a peer-reviewed 
journal. If a follow up study is needed, that would be pursued prior to publication.  
 
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