Pancreas volume measurement in patients with Type 2 diabetes using magnetic resonance imaging-based planimetry

Abstract

Background/objectives

To compare pancreas volume (PV) measurement using MRI-based planimetry in patients with Type 2 diabetes mellitus (DM) to PV in normoglycemic individuals.

Methods

Our institutional review board granted approval of this retrospective study with waiver of informed consent. We searched 2296 consecutive abdominal MRI studies performed at our hospital on patients with no pancreas pathology between September 1, 2010 and February 28, 2013, for those who also had a fasting plasma glucose and/or hemoglobin A1C within six months of the MRI examination. For those patients who met biochemical criteria for DM, we used medication and clinical records to confirm that 32 of these patients had Type 2 DM. The pancreas contours of 32 Type 2 diabetics and 50 normoglycemic individuals were then traced on non-gadolinium T1-weighted 3D fat suppressed gradient echo images by a radiologist trained in abdominal MRI to calculate PV. PV index (PVI) was calculated as PV/weight to adjust PV for each patient's weight. PVs and PVIs in both cohorts were compared using t-tests and regression models correcting for weight, age and gender.

Results

Patients with Type 2 DM had significantly lower PVs than normoglycemic individuals (72.7 ± 20.7 cm³ versus 89.6 ± 22.7 cm³, p < 0.001), and significantly lower PVIs (1.0 ± 0.3 cm³/kg versus 1.3 ± 0.3 cm³/kg, p < 0.001). Using regression models, we found that given the same age, weight and gender, the PV in a patient with Type 2 DM was 17.9 mL (20%) lower compared to a normoglycemic individual (p < 0.001).

Conclusion

PV is reduced in Type 2 DM compared to normoglycemic individuals and can be measured using MRI without contrast injection.

Introduction

Pancreas volume (PV) is altered by normal events such as aging or weight gain. For example, PV increases in a linear fashion from birth to age 20; decreases following age 60 [1], [2] and PV shows a linear correlation with body weight [3], [4]. Pancreatic atrophy has been associated with a variety of pathological conditions, such as cystic fibrosis, pancreatic adenocarcinoma, and Type 1 and 2 diabetes mellitus (DM) [5], [6], [7], [8]. There has been an evolving interest in PV alteration over the course of DM [2], [3], [8], [9], [10], [11]. Both Type 1 and Type 2 DM are associated with decreased PV, attributed in part to chronic inflammation [11], [12] and loss of the trophic effects of insulin [8], [9], [11], [13].

The majority of studies measuring PV in diabetes have been conducted using computed tomography (CT) [2], [10], [11], [13] or ultrasonography [14]. Ultrasonography only provides a rough estimation of PV due to the lack of standardized measurement capability and operator dependence. It is difficult to visualize the pancreas on ultrasound especially in obese individuals. Very often there may be overlying bowel gas limiting visualization. The distal part of the tail of the pancreas is commonly not well visualized on ultrasound [14]. CT utilizes ionizing radiation that may be harmful with repeated scans for monitoring or screening [3].

To our knowledge, the use of magnetic resonance imaging (MRI) in measuring PV has been limited. Only a few studies to date have investigated the use of MRI for PV measurement [3], [4], [15], [16] in DM. Moreover the focus of those studies was normal subjects, Type 1 DM [3], [4] or cystic fibrosis-related diabetes [15] and the cohort sizes were small.

The few studies using MRI to measure PVs in DM have done so in Type 1 DM, though Type 2 DM is much more common. PVs in Type 1 DM are significantly lower than that of normoglycemic individuals [3]. The volume difference between normoglycemics and Type 2 diabetics has been less striking [2], [10] and has only been measured with CT to date.

We believe that it is important to measure this difference in PVs between Type 2 diabetics and normoglycemic individuals with MRI, without radiation exposure as in CT. Type 2 DM is important to study in this context because it is more prevalent, it poses a large health and economic burden on society, and it is more representative of the distribution of DM subtypes in a typical adult population.

The principal advantages of MRI over other imaging modalities are that: it does not involve ionizing radiation; spatial resolution in 3D MRI acquisitions has evolved to the point that volumetric image data sets can be manipulated in any plane; and there are numerous inherent contrast mechanisms that allow for excellent contrast resolution without administration of an exogenous contrast agent. Though there are many potential clinical applications of measuring PV with such a safe and accessible technique [17], [18], our aim in this study was to measure PV using planimetry based on a simple but accurate MRI pulse sequence in patients who have Type 2 DM, compared to patients who are normoglycemic. We hypothesized that PV will be decreased in patients with Type 2 DM compared to normoglycemic patients.