Characterization of quantitative susceptibility mapping in the left ventricular myocardium.

BACKGROUND: Myocardial quantitative susceptibility mapping (QSM) may offer better specificity to iron than conventional T2* imaging in the assessment of cardiac diseases, including intra-myocardial hemorrhage. However, the precision and repeatability of cardiac QSM have not yet been characterized. The aim of this study is to characterize these key metrics in a healthy volunteer cohort and show the feasibility of the method in patients. METHODS: Free breathing respiratory-navigated multi-echo 3D gradient echo images were acquired, from which QSM maps were reconstructed using the Morphology Enhanced Dipole Inversion toolbox. This technique was first evaluated in a susceptibility phantom containing tubes with known concentrations of gadolinium. In vivo characterization of myocardial QSM was then performed in a cohort of 10 healthy volunteers where each subject was scanned twice. Mean segment susceptibility, precision (standard deviation of voxel magnetic susceptibilities within one segment), and repeatability (absolute difference in segment mean susceptibility between repeats) of QSM were calculated for each American Heart Association (AHA) myocardial segment. Finally, the feasibility of the method was shown in 10 patients, including four with hemorrhagic infarcts. RESULTS: The phantom experiment showed a strong linear relationship between measured and predicted susceptibility shifts (R2 > 0.99). For the healthy volunteer cohort, AHA segment analysis showed the mean segment susceptibility was 0.00 ± 0.02 ppm, the mean precision was 0.05 ± 0.04 ppm, and the mean repeatability was 0.02 ± 0.02 ppm. Cardiac QSM was successfully performed in all patients. Focal iron deposits were successfully visualized in the patients with hemorrhagic myocardial infarctions. CONCLUSION: The precision and repeatability of cardiac QSM were successfully characterized in phantom and in vivo experiments. The feasibility of the technique was also successfully demonstrated in patients. While challenges still remain, further clinical evaluation of the technique is now warranted. TRIAL REGISTRATION: This work does not report on a health care intervention.

Feasibility of cardiac MR thermometry at 0.55†T.

Radiofrequency catheter ablation is an established treatment strategy for ventricular tachycardia, but remains associated with a low success rate. MR guidance of ventricular tachycardia shows promises to improve the success rate of these procedures, especially due to its potential to provide real-time information on lesion formation using cardiac MR thermometry. Modern low field MRI scanners (<1 T) are of major interest for MR-guided ablations as the potential benefits include lower costs, increased patient access and device compatibility through reduced device-induced imaging artefacts and safety constraints. However, the feasibility of cardiac MR thermometry at low field remains unknown. In this study, we demonstrate the feasibility of cardiac MR thermometry at 0.55 T and characterized its in vivo stability (i.e., precision) using state-of-the-art techniques based on the proton resonance frequency shift method. Nine healthy volunteers were scanned using a cardiac MR thermometry protocol based on single-shot EPI imaging (3 slices in the left ventricle, 150 dynamics, TE = 41 ms). The reconstruction pipeline included image registration to align all the images, multi-baseline approach (look-up-table length = 30) to correct for respiration-induced phase variations, and temporal filtering to reduce noise in temperature maps. The stability of thermometry was defined as the pixel-wise standard deviation of temperature changes over time. Cardiac MR thermometry was successfully acquired in all subjects and the stability averaged across all subjects was 1.8 ± 1.0°C. Without multi-baseline correction, the overall stability was 2.8 ± 1.6°C. In conclusion, cardiac MR thermometry is feasible at 0.55 T and further studies on MR-guided catheter ablations at low field are warranted.

Bleeding Complications in Patients With Severe Frostbite Injury.

Frostbite is caused by exposure to cold temperatures and can lead to severe injury resulting in amputations. Tissue plasminogen activator (tPA) is a thrombolytic agent that has demonstrated efficacy preventing amputation in frostbite patients. The goal of frostbite management with tPA is to salvage tissue without causing clinically significant bleeding complication. The purpose of this study was to characterize bleeding complications in severe frostbite patients managed with and without tPA. Retrospective chart review of severe frostbite patients admitted to a single ABA verified burn center. Bleeding events were grouped: category 0: no bleed; category 1: bleed not resulting in change or intervention; category 2: bleed resulting in change of management; and category 3: bleed resulting in change of management and intervention. Over a 7-year period, 188 patients were included in the study. Most patients had no documentation suggesting a bleeding complication: 69.7% category 0, 19.1% category 1, 4.8% category 2, and 6.4% category 3. There was no significant difference in category 2 or 3 bleeding complications between patients treated with or without tPA. Overall, 9 of the 143 patients (6.3%) treated with tPA had a category 2 or 3 bleeding complication within 12 hours of tPA completion and 12 of 143 (8.4%) within 24 hours of tPA completion. Based on the low risk of severe bleeding and significant benefit relative to limb or digit salvage demonstrated in this study, we conclude that tPA is safe and effective for the treatment of frostbite in appropriately selected patients.

The Effects of Rapid Rewarming on Tissue Salvage in Severe Frostbite Injury.

Frostbite is a high morbidity injury caused by soft tissue freezing, which can lead to digit necrosis requiring amputation. Rapid rewarming is a first-line treatment method that involves placing affected digits into a warm water bath. This study aims to assess the clinical practices for frostbite at facilities outside of dedicated burn centers, and any impact these practices have on tissue salvage. Retrospective chart review at a single burn center identified frostbite patients admitted directly or as transfers over a 7-year period. Records were reviewed to identify initial treatment strategies. If given, time to thrombolytics from admit was noted. Tissue salvage rates were calculated from radiologically derived tissue at-risk scores and final amputation scores. One-hundred patients were transferred from outside facilities, and 108 were direct admissions (N = 208). There was no significant difference in group demographics. Rapid rewarming was the initial treatment modality more commonly in direct admit patients (P = .016). The use of rapid rewarming did not correlate with tissue salvage (P = .112). Early use of thrombolytics had a positive impact on tissue salvage (P = .003). Thrombolytics were given 1.2 hours earlier in direct admit patients (P = .029), however there was no difference in tissue salvage rates between the groups (P = .127). Efforts should focus on larger scale study to further assess the effectiveness of rapid rewarming. Although rapid rewarming did not significantly impact tissue salvage in this study, we continue to recommend its use over less studied treatment methods, and continue to view it as an important bridge to burn center transfer and administration of thrombolytic therapy.

An Institutional Protocol for the Treatment of Severe Frostbite Injury-A 6-Year Retrospective Analysis.

The treatment of severe frostbite injury has undergone rapid development in the past 30 years with many different diagnostic and treatment options now available. However, there is currently no consensus on the best method for management of this disease process. At our institution, we have designed a protocol for severe frostbite injury that includes diagnosis, medical treatment, wound cares, therapy, and surgery. This study assess the efficacy of our treatment since its implementation six years ago. During this time, all patients with severe frostbite injury were included in prospective observational trial of the protocol. We found that this protocol results in significant tissue salvage with over 80.7% of previously ischemic tissue becoming viable and not requiring amputation. We also were able to improve our center's efficiency over the course of six years and now our current average time from rapid rewarming to delivery of thrombolytics is under six hours.

Outpatient management of steroid-induced hyperglycaemia and steroid-induced diabetes in people with lymphoproliferative disorders treated with intermittent high dose steroids.

High dose steroids (HDS) are used in the treatment of haematological malignancies. The reported risk of steroid-induced diabetes (SID) is high. However, screening is not consistently performed. We implemented a protocol for detection and management of SID and steroid-induced hyperglycamia (SIH) in haematology outpatients receiving HDS. Eighty-three people were diagnosed with a lymphoproliferative disorder, of whom 6 had known Type 2 diabetes. Fifty-three people without known diabetes were screened by HbA1c and random venous plasma glucose. All patients (n = 34) subsequently prescribed HDS checked capillary blood glucose (CBG) pre-breakfast and pre-evening meal. Treatment algorithms used initiation and/or dose titration of gliclazide or human NPH insulin, aiming for pre-meal CBG 5-11 mmol/l. Type 2 diabetes was identified in 4/53 people screened (7.5%). Of 34 people treated with HDS, 17 (44%) developed SIH/SID. All 7 people with Type 2 diabetes developed SIH and 3 required insulin. Of 27 people without known diabetes, 8 (30%) developed SID and 1 required insulin. Pre-treatment HbA1c was higher in people who developed SID compared to those that did not (p = 0.002). This is the first report of a SID/SIH detection and treatment protocol for use in people with lymphoproliferative disorders receiving intermittent HDS, demonstrating its feasibility and safety.