The goal of this study is to investigate the encapsulation of fluid collections in patients with ANP using serial MRI.

The main questions it aims to answer are:

• Evaluating the timing of encapsulation of necrotic fluid collection using serial non-enhanced MRI.
• Identifying the factors that affect the timing of encapsulation of necrotic fluid collections Participants will undergo serial MRI scans (all with the same protocol) performed starting at day 15. Subsequent scans will be performed at 5 days interval till the clinically significant encapsulation (for all the collections in an individual patient) is seen or patients are excluded from the protocol due to intervention.

Consecutive patients with ANP presenting to the hospital within 2 weeks from the pain onset will be recruited. They will undergo serial non-contrast MRI starting at day 15 and every 5 days thereafter, till complete encapsulation of PFC. Ultrasound evaluation of the collection will be performed on the day of MRI by a radiologist not involved in evaluation of MRI. The site and volume of collection as well as thickness and completeness of the capsule and solid content within the collection will be recorded independently by two radiologists. The timing of clinically significant (>50% of PFC show capsule) and complete encapsulation will be recorded. The proportion of collections encapsulating in each week after 2nd week of illness will be recorded. The association between timing of encapsulation and clinical/biochemical parameters will be assessed. The correlation between the degree of encapsulation and percentage of solid components will also be documented. Multivariate analysis will be performed to identify factors associated with timing of encapsulation.

Inclusion Criteria:

1. Acute necrotizing pancreatitis
2. Presentation to hospital within 2 weeks of pain onset

2. Willing to give informed consent

Exclusion Criteria:

1. Contraindications to non- enhanced MRI (Claustrophobia, cardiac pacemaker, cochlear implant).
2. Acute on chronic pancreatitis
3. Mechanical ventilation, ionotropic support (precluding safe environment in MRI).
4. Drainage or aspiration of a collection prior to recruitment

Consecutive patients with ANP presenting to the hospital within 2 weeks from the pain onset will be recruited. They will undergo serial non-contrast MRI starting at day 15 and every 5 days thereafter, till complete encapsulation of PFC. Ultrasound evaluation of the collection will be performed on the day of MRI by a radiologist not involved in evaluation of MRI.