ARFI for ACUTE PANCREATITIS

Discussion

In this study, all 88 patients (100%) with acute pancreatitis had a diagnosis by ARFI elastography, whereas only 47 patients (53.4%) had a correct diagnosis by B-mode sonography. Computed tomographic scans were performed on 41 of the 88 patients, and only 31 of these patients (76%) had a correct diagnosis. These results demonstrate the high success rate of ARFI elastography for diagnosing acute pancreatitis and the superiority of this method to B-mode sonography and CT.

Success rates for identifying abnormalities on sonography in patients with acute pancreatitis range from 33% to 90%.³ Sonography is a useful tool for detecting gallstones, which are important in the etiology of acute pancreatitis. It is also used to exclude other potential causes of acute abdominal pain. However, because the pancreatic parenchyma is difficult to detect in obese patients and patients with flatulence, diagnosis of acute pancreatitis based on sonography can be difficult.³

Computed tomography is accepted as the primary imaging technique for diagnosis of acute pancreatitis and detection of its severity.³ The advantages of CT lie in its abilities to image retroperitoneal organs, abdominal ligaments, the mesentery, the omentum, and the pancreas. The diagnostic sensitivity of CT for acute pancreatitis ranges from 77% to 92%.^14–16 In patients with less severe acute pancreatitis, CT results may be negative.² In our study, 10 patients with CT scans that revealed a normal pancreatic size, a normal pancreatic density and heterogeneity, and no peripancreatic inflammation or fluid had a diagnosis of acute pancreatitis by ARFI imaging. This finding suggests that ARFI elastography can successfully detect pancreatic inflammation visually and quantitatively even in cases of less severe pancreatitis.

The inflammation observed in acute pancreatitis may be segmental rather than diffuse. With a frequency of 18%, the segmental form is rare,^17,18 generally involves the pancreatic head, and occurs with stones.^19–21 We found that the inflamed segments of the pancreas had color scores higher than 2 on the VTI images, and the unaffected areas had scores of 1 or 2. In 10 patients (11.3%) with segmental involvement, only the head was affected, and 5 (5.6%) had involvement of the head and a portion of the body. Among all of the patients with segmental involvement, the VTQ values were higher for inflamed tissue sites than those of noninflamed or less inflamed sites. These data show that ARFI elastography can be used to visualize the location of inflammation in the pancreas and to determine whether that inflammation is segmental.

During the arterial phase of intravenous administration of a contrast medium bolus, the normal pancreas should enhance homogeneously. Mild inflammation and interstitial edema do not interfere with the expected homogeneous enhancement of the gland. When necrosis is present, an absence of contrast enhancement, liquefaction, and changes in the density or signal intensity of the gland are observed. A study of a series of 93 patients found an overall accuracy rate of 85% for CT, with 100% sensitivity for extensive glandular necrosis.²² In this present study, the virtual and quantitative VTQ values for the necrotic areas were evaluated for the 6 patients with necrotizing pancreatitis. Computed tomography is more accurate than sonography for detection of necrotic areas in the pancreatic parenchyma. The necrotic areas in the pancreas appeared enlarged and hypoechoic on B-mode sonography, which suggests decreased stiffness, and produced low VTQ values on ARFI imaging. The VTI scores for the enlarged glands were either 1 or 2, and quantitative measurements of the necrotic areas ranged from 0.5 to 1.2 m/s. Based on these results, ARFI elastography may be helpful for diagnosis of necrotic pancreatitis.

Only 1 previous study in the literature evaluated the diagnosis of acute pancreatitis with ARFI elastography. In that study, patients with acute pancreatitis and those with resolving pancreatitis were compared with patients who had chronic pancreatitis and a control group.²⁰ The authors of that study reported average VTQ values of 2.38 m/s for the patients with acute pancreatitis and 1.28 m/s for those with a normal pancreas. We found a mean VTQ value of 2.14 ± 0.74 m/s and a range of 1.1 to 4.47 m/s for the patients with acute pancreatitis. The mean VTQ value for normal parenchyma was 1.17 ± 0.24 m/s and ranged from 0.6 to 1.63 m/s. A previous study reported VTQ values ranging from 1.48 to 2.50 m/s in acute resolving pancreatic necrosis, whereas we found that VTQ values ranged from 0.5 to 1.2 m/s in necrosis. In the previous study, the VTQ cutoff value was chosen as the upper limit of the 95% confidence interval (1.792–2.157 m/s) of the mean VTQ value of the entire study population (2.088 ± 1.155 m/s) and was rounded to 2.2 m/s. The acute and resolving pancreatitis groups were distinguished with 97.1% sensitivity and 92.9% specificity. In contrast, we found that VTQ distinguished pancreatitis from normal parenchyma with 100% sensitivity and 98% specificity when the cutoff point was defined as 1.63 m/s. The differences between the previous study and our study may be attributable to our study’s exclusion of patients with chronic pancreatitis or the combination of patients with acute and resolving pancreatitis in the previous study.

Our study had limitations. First, the quality of the images obtained with ARFI elastography depends on the abilities of the operator. Optimal images and quantitative results cannot be obtained from patients with tachypnea, tachycardia, or obesity. In obese patients, the pancreas is located deep inside the body (>8 cm), and this evaluation cannot be performed. Another limitation of the ARFI technique is limited visualization of the pancreas on B-mode sonography. Since ARFI evaluation of the pancreas starts after B-mode sonography, poor visualization of the pancreas on B-mode sonography may result in inadequate interpretation of the pancreas on VTI and VTQ. In our study, we excluded obese patients, since visualization of the pancreas on B-mode sonography was difficult. Additionally, the relationship between ARFI elastographic results and the severity of pancreatitis was not assessed in terms of morbidity and mortality. However, we believe that this study will lead to other, more exhaustive studies in the future.

In conclusion, ARFI elastography is a noninvasive, radiation-free, rapid, and reproducible imaging method that can efficiently diagnose acute pancreatitis at hospital admission. It provides reliable results that visualize the distribution of inflammation in glands, peripancreatic inflammation, and necrosis. Furthermore, the positive diagnoses yielded by elastography in patients with negative CT findings are novel results.

ARFI for NORMAL PANCREAS at MEDIC CENTER=

Of 30 normal pancreas from 30 male inviduals, age 20-40 yo,  we have mean elastic velocity of pancreas = 0.96+/-0.16 m/s (range 0.6-1.19m/s) while according to Goya et al in the text above, the mean VTQ value for normal parenchyma was 1.17 ± 0.24 m/s and ranged from 0.6 to 1.63 m/s. 

NHÂN CA VIÊM TỤY CẤP N 3 TẠI MEDIC.
Sau uống rượu đau bụng nhiều từ 3 ngày trước,  bệnh nhân được khám siêu âm, thử máu amylasemia không tăng, lipase tăng và CRP tăng. CT cho thấy viêm tụy phần đuôi, có tạo nang giả như siêu âm ARFI  tụy.

Ca viêm đầu tụy khu trú tái phát:
Tổn thương phù nề echo poor có nang hóa vùng đầu=76x88mm, ARFI=2,6-2,8m/s;  thân và đuôi bình thường. ARFI thân và đuôi v=1,9cm/s

CA VIÊM TỤY MẠN [UỐNG RƯỢU]

Mô tụy xơ hóa toàn bộ, có vôi hóa rải rác, kích thước=23-13-17mm. Ông tụy chính Wirsung giãn 7-12mm không sỏi, thành dày nhiễm cứng. 

ARFI mô tụy= 1,78-1,84m/s