Results: CT Clinical Practice: Data acquisition protocols

1. Is a three phase CTA of the pancreas indicated for pancreatitis? Specifically, does the addition of the arterial phase improve diagnosis of parenchymal necrosis (or is the venous/parenchymal phase best for this diagnosis)?

2. Why do you use still arterial phase in you MDCT protocol for pancreas (See Radiology, October 2003, p. 81)

3. How often and under what circumstances does your institution use no ORAL contrast in (1) initial and (2) follow up CT of acute pancreatitis? Some of our surgeons feel that since they are 'resting bowel' as part of treatment, oral contrast may cause exacerbation of symptoms. I haven't seen any literature to support that, have you?

4. Could you tell me when it is necessary to perform non-contrast pancreas before the arterial and venous phase? Some of my senior co-workers (CT techs) say if the patient had a non-con pancreas within the last few months you can just do arterial and venous phases. And if not, you have to do the non-contrast as well as the other phases. But they do not have an explanation for it.

References

McNulty NJ. Francis IR. Platt JF. Cohan RH. Korobkin M. Gebremariam A. Multi--detector row helical CT of the pancreas: effect of contrast-enhanced multiphasic imaging on enhancement of the pancreas, peripancreatic vasculature, and pancreatic adenocarcinoma. Radiology. 2001; 220(1):97-102.

• Summary: This study included 28 patients with pancreatic adenocarcinoma and 49 patients with a normal appearing pancreas. Both quantitative and qualitative evaluation were conducted to determine the utility of arterial phase (AP), pancreatic parenchymal phase (PPP) and portal venous phase acquisitions (PVP). Results showed that the pancreas enhanced maximally during the PPP. Both PPP and PVP demonstrated superior subjective and quantitative tumor-to-pancreas contrast compared to AP. Furthermore, because maximal arterial enhancement was noted during PPP and maximal venous enhancement during PVP, the authors recommend using these 2 acquisition series exclusively to detect and stage pancreatic tumors, unless CT angiography is required.

Vargas R. Nino-Murcia M. Trueblood W. Jeffrey RB Jr. MDCT in Pancreatic
adenocarcinoma: prediction of vascular invasion and resectability using a multiphasic technique with curve planar reformations. AJR 2004; 182(2): 419-425.

• Summary: In this recent study, 8 slice MDCT was performed using water as an oral contrast agent and 150 ml of 300 mgI/ml nonionic contrast, infused at 4 cc/second. At 40 seconds, the acquisition was initiated with 1.25 mm nominal thickness, reconstructed at .5 mm intervals. The second phase scan was performed at 70 seconds with 5 mm thickness and 5 mm recontruction interval. Twenty-five patients were studied, and CT with curved planar reconstructions were used to predict resectability. The negative predictive value was 87% for resectability. For detecting vascular invasion, MDCT was 99% accurate with a negative predictive value of 100%.

Fletcher JG. Wiersema MJ. Farrell MA. Fidler JL. Burgart LJ. Koyama T. Johnson CD. Stephens DH. Ward EM. Harmsen WS. Pancreatic malignancy: value of arterial, pancreatic, and hepatic phase imaging with multi-detector row CT. Radiology. 2003; 229(1):81-90.

• Summary: This study validates the previous work of McNulty, suggesting that the arterial phase is unnecessary for detecting pancreatic cancer. In this study, acquisitions were performed during arterial, pancreatic and hepatic phases. The scanners used were LightSpeed Plus and LightSpeed QX/I, and a sliding scale of timing was used, tailored to infusion rates of 3, 4 and 5 ml/second, to yield arterial, pancreatic and hepatic phase acquisitions. Thirty-nine patients with suspected pancreatic cancer were imaged. Quantitative and qualitative review of the images was performed, with comparison to clinical follow up and pathology. Results showed that the pancreatic phase was optimal for tumor-to-pancreas contrast, and pancreatic and hepatic phases were superior to arterial phase for tumor detection. This study reported that hepatic phase was most sensitive for vascular invasion.