Delayed magnetic resonance hepatic imaging with gadolinium-DTPA.

Magnetic resonance imaging of the liver was performed on 11 rabbits (3-5 kg) before and at 4, 5 and 6 hours after the intravenous administration of 0.3 mM/kg Gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) to determine if hepatocytes exhibit delayed excretion of Gd-DTPA, similar to the delayed hepatic excretion of iodinated contrast agents. Imaging was performed at 0.5 Tesla in the axial plane using a spin echo sequence of TR/TE, 250/20 milliseconds. Precontrast and postcontrast intensity changes for liver and muscle were standardized and compared over time. The average percent of postcontrast enhancement for liver and muscle, respectively was: 30.6 +/- 9.5% and 17.3 +/- 17.0% immediately postcontrast; 9.7 +/- 13.6% and 1.6 +/- 13.8% at 4 hours; 9.6 +/- 7.8% and 4.3 +/- 13.2% at 5 hours; and 11.0 +/- 7.8% and 4.1 +/- 11.7% at 6 hours. We conclude that there is not significant hepatocyte excretion of Gd-DTPA at 4 to 6 hours postcontrast injection in rabbits and that this may not be an advantageous paramagnetic contrast strategy for focal hepatic lesion detection.

Manganese dipyridoxyl diphosphate. Effect of dose, time, and pulse sequence on hepatic enhancement in rats.

We used an animal model to investigate the hepatic enhancement characteristics of manganese dipyridoxyl diphosphate (MnDPDP) related to time, dose, and pulse sequence. The contrast doses selected were in the human tolerance range. Using an SE 300/15 pulse sequence, maximum mean hepatic enhancement of 45% (8 mumols/kg) and 58% (12 mumols/kg) over baseline was seen during a plateau maintained between 5 and 50 minutes postinjection in the 8 mumols/kg group, and between 10 and 90 minutes in the 12 mumols/kg group. This plateau was followed by a very gradual decline in hepatic enhancement. Using either 4 or 8 mumols/kg, there was a significant increase in postcontrast hepatic intensity on all relatively T1-weighted pulse sequences (spin echo [SE] 300/15, inversion recovery [IR] 1400/20/400, gradient echo [GE] 47/13/80 degrees, and GE 60/20/30 degrees) except GE 47/13/80 degrees at 4 mumols/kg. At 8 mumols/kg there was superior enhancement, with IR 1400/20/400 and SE 300/15, but at 4 mumols/kg there was no consistently superior sequence. None of the relatively T2-weighted pulse sequences (SE 2000/50, SE 2000/100, or GE 100/30/20 degrees) demonstrated a significant change in hepatic intensity using either dose of contrast. The data suggest that the best combination of dose, pulse sequence, and time for hepatic imaging with MnDPDP is 8 mumols/kg using heavily T1-weighted sequences 5 to 60 minutes following contrast administration.

Magnetic resonance imaging after arterial portography with manganese dipyridoxal diphosphate.

RATIONALE AND OBJECTIVES: The authors assess performing hepatic magnetic resonance imaging (MRI) after arterial portography with manganese dipyridoxal diphosphate (MnD-PDP), a hepatobiliary contrast agent, as an invasive but potentially highly sensitive means of focal lesion detection. METHODS: Eight pigs underwent superior mesenteric artery catheterization and injection of 10 mumol/kg MnDPDP. Magnetic resonance imaging at 1.5 T (SE-140/10) was performed before, then at 15 and 30 minutes after injection. Seven or more days later, the same MRI protocol was performed after intravenous injection of 10 mumol/kg MnDPDP. RESULTS: Fifteen minutes after intra-arterial injection, enhancement of the liver predominated (86 +/- 13%), followed by the renal cortex (44 +/- 14%), pancreas (26 +/- 9%), and spleen (14 +/- 9%). At 30 minutes, enhancement of renal cortex significantly increased (50 +/- 14%). There was no significant difference in enhancement of the liver, spleen, pancreas, or renal cortex when we compared intra-arterial and intravenous administration. CONCLUSION: After the injection of 10 mumol/kg MnDPDP into the superior mesenteric artery of pigs there is no significant difference in visceral organ enhancement compared to intravenous administration. The data suggests that the hepatocyte binding sites may be overwhelmed by this dose and/or injection rate of MnDPDP.

Magnetic resonance imaging of the liver. Technique.

Image quality and the ability to detect disease in the liver with magnetic resonance (MR) imaging are critically dependent on the pulse sequences used and on the reduction of motion artifact. Selection of appropriate pulse sequences depends on a number of factors including magnetic field strength, equipment manufacturer, and availability of pulse sequences and motion artifact reduction techniques on the individual equipment used. This article summarizes some of the current methods available for reducing motion artifacts, discusses selection of imaging parameters for maximizing hepatic lesion detection, and reviews research on the use of contrast agents for MR imaging of the liver.

Are hepatic and muscle T2 values different at 0.5 and 1.5 Tesla?

In an effort to determine whether T2 values of liver and muscle change with increasing field strength, 144 abdominal MR examinations were retrospectively evaluated. These patients were evaluated with a dual echo T2-weighted spin-echo sequence. Eighty-two of the examinations were performed at 0.5 Tesla and 72 at 1.5 Tesla (T). Eleven of the patients were evaluated with both MR systems with the same sequences. T2 values were also obtained from a Fe NH4(SO4)2 12H2O phantom. The T2 values of liver decreased from 57.8 +/- 11.3 at 0.5 T to 43.7 +/- 8.3 at 1.5 T. The T2 values of muscle decreased from 44.2 +/- 9 at 0.5 T to 35.4 +/- 7.2 at 1.5 T. Patients who were examined on both systems also demonstrated a decrease in both liver and muscle T2 values. For concentrations in the range of hepatic T2's, the phantom demonstrated a decrease in T2 values from 0.5 to 1.5 T ranging from 20.3 to 23.4%. All the T2 changes were statistically significant (p less than .05). The findings suggest that T2 values may depend on field strength, or may vary due to other hardware-related differences.

Hepatic metastases.

Metastatic disease is the most common cause of malignant liver lesion in the United States. This article focuses on the MR techniques utilized for evaluation of the liver for metastatic disease, the MR appearance of hepatic metastases, and several contrast agents being developed to further improve detection of focal hepatic lesions by MR imaging.

Magnetic resonance imaging of the kidneys and adrenal glands.

A simple renal cyst will have low signal intensity on T1-weighted SE images with short TE and short TR because of the long T1 values of the cyst fluid. With increasing TE and TR, cysts demonstrate increased signal intensity due to the long T2 values of the cyst fluid. On T1-weighted images a complicated cyst will have higher signal intensity than a simple cyst; it may not be possible to differentiate these complicated cysts from solid masses. MRI seems to be useful in identifying simple cyst fluid and, therefore, has potential in characterization of cystic lesions considered complex by CT or ultrasound. Unfortunately, imaging techniques have not yet been optimized, diagnostic criteria are somewhat vague, and accuracy has not been established in a representative patient population. Solid masses often can be identified and differentiated from simple, uncomplicated cysts on MR images. The inability to differentiate among various types of solid tumors or to separate these from complicated cysts or inflammatory masses remains a limitation. Most lesions are more readily seen on contrast-enhanced CT than on MR images and therefore the role of MRI in the detection and diagnosis of renal cell carcinoma remains limited. Although the high detection rate of renal cell carcinoma is encouraging, CT is still more sensitive than MR in demonstrating solid lesions less than 3 cm in diameter. MRI cannot be used as a screening modality for renal tumors. MRI seems quite helpful in the staging of renal cell carcinoma. Macroscopic extension into the perinephric fat, tumor extension into the renal vein and the inferior vena cava, and macroscopic metastases to other organs are readily seen. Furthermore, differentiation between enlarged nodes and vessels is possible with MRI. Some authors recommended the use of MRI to stage renal cell carcinoma in patients with known contraindication to contrast, prior suboptimal bolus contrast enhanced CT scan, and equivocal CT findings. MRI can replace the inferior vena cavagram in the staging work-up and MR may be superior to CT for planning the surgical approach in Stage IIIA lesions by determining the upper extent of tumor thrombus within the inferior vena cava or the right atrium.(ABSTRACT TRUNCATED AT 400 WORDS)

Fast spin-echo imaging of the abdomen during breath-holding: an alternative to RASE and other fast imaging techniques.

We have developed a rapidly acquired T1-weighted spin-echo pulse sequence that uses gradient echo-like parameters of TR 70 ms, TE 10 ms, NEX-1 (SE 70/10/1) with large pulse angles, and presaturation. This sequence yields two images of the abdomen during a comfortable breath-hold of 9 s. Preliminary phantom studies with this sequence demonstrated that peak signal-to-noise ratios occurred at pulse angles of 120 degrees and 135 degrees. Compared to this rapidly acquired sequence, a conventional T1-weighted spin-echo sequence of TR 140 ms, TE 10 ms, NEX-4 demonstrated 2.8 times the signal-to-noise ratio, 2.6 times the liver-spleen contrast-to-noise ratio but only 1.6 times the contrast-to-artifact ratio. When normalized for the imaging time, however, there was little difference in the signal-to-noise and contrast-to-noise ratios, although the SE 70/10/1 demonstrated 2.0 times the contrast-to-artifact ratio. We conclude that for abdominal imaging the SE 70/10/1 is an excellent alternative to RASE and other fast imaging techniques, and, although there are inherently low signal-to-noise ratios, it may be particularly useful when coupled with a paramagnetic contrast agent.

Mesoatrial shunt for the treatment of Budd-Chiari syndrome: radiologic evaluation in eight patients.

The construction of a mesoatrial shunt for portal decompression is one of the surgical procedures used for the treatment of Budd-Chiari syndrome. The results of the imaging procedures performed in eight patients treated in this fashion were retrospectively analyzed. All of the patients had angiography; seven had MR imaging and two had Doppler sonography. The demonstration of shunt patency, stenosis, or occlusion by MR and Doppler sonography was confirmed by angiography in all cases. We conclude that MR imaging may serve as an accurate screening method to assess shunt patency and to determine which patients require angiography to obtain hemodynamic data. Doppler sonography may also be a useful screening method, but additional data must be obtained to assess its role in evaluation of shunt patency.

CT angiography and CT arterial portography in evaluation of hepatic adenomas.

OBJECTIVE: Our goal was to evaluate the contribution of CT arterial portography (CTAP) and CT angiography to accurate determination of disease extent in patients with known hepatic adenomas. MATERIALS AND METHODS: Imaging results were reviewed in three women with known hepatic adenomas, all of whom had percutaneous biopsy to confirm the diagnosis. Results of CTAP studies in all patients as well as results of CT arteriography in one patient were compared with routine dynamic CT studies in all three and with MRI studies in two. RESULTS: The CTAP and CT arteriography demonstrated multiple additional lesions in all patients as compared with routine dynamic CT and MRI studies. In one of the patients who was found to have hepatic adenomatosis, the degree of tumor involvement changed the operative procedure from partial hepatectomy to liver transplantation. CONCLUSION: In patients with known hepatic adenomas who require surgery, CTAP provides more accurate preoperative staging of extent of liver replacement with tumor.

Recurrent tumor after resection of hepatic metastases from colorectal carcinoma: location and time of discovery as determined by CT.

OBJECTIVE: Despite studies showing increased survival rates for patients after surgical resection of hepatic metastases, recurrences occur in 75% of treated patients. The purpose of this study was to determine the location and time of discovery of recurrent tumor on CT scans after resection of hepatic metastases from colorectal carcinoma. MATERIALS AND METHODS: In a 6-year period, 32 patients (16 men and 16 women) who had undergone partial hepatic resection for colorectal metastases had follow-up CT at our institution. A total of 125 CT examinations of the chest and abdomen were retrospectively reviewed for the presence and location of recurrent disease. Recurrence was either confirmed by biopsy (n = 12) or presumed on the basis of growth of new lesions (n = 17). RESULTS: With a mean follow-up of 22 months (range, 1-60 months), recurrence was found at 29 sites in 25 patients. Thirteen sites were hepatic, and 16 were extrahepatic. Three patients had both hepatic and pulmonary disease. Recurrence within the liver was away from surgical margins in 11 (85%) of 13 patients at 14 +/- 7 months and adjacent to a surgical margin in the remaining two patients (15%) at 17 +/- 1 months. Extrahepatic recurrences were discovered in the lung in 11 (69%) of 16 patients at 21 +/- 12 months; in an adrenal gland in two patients (13%) at 19 +/- 5 months; in lymph nodes of the porta hepatis in one patient (6%) at 11 months; at the primary colonic anastomosis in one patient (6%) at 3 months; and in a retroperitoneal lymph node in the remaining patient (6%) at 12 months. CONCLUSION: Surgery was effective in treating the preoperatively detected hepatic metastases. Only two of 25 patients had recurrence related to a hepatic surgical margin. Most recurrences occur more than 1 year after surgery, most often in lung or liver away from surgical margins, and they probably represent small metastases undetectable with current preoperative or intraoperative techniques.

Portal venous gas after hepatic transplantation: sonographic detection and clinical significance.

In seven (18%) of 39 liver transplantation patients, serial Doppler sonographic examinations performed in the first 2 weeks after the transplantation showed transient, highly echogenic nonshadowing particles moving within the portal vein, believed to be portal venous air. This finding was associated with sepsis in one patient, a positive stool culture for Clostridium difficile in another, and postoperative ileus in a third patient. A fourth patient had primary graft failure and required a second transplant. No potential cause was found in the other three patients. None of the patients had bowel infarction or necrosis. The finding was not associated with transplant rejection or graft infection. We conclude that the sonographic finding of portal venous gas is common in the first 2 weeks after hepatic transplantation and may not have grave prognostic significance.

Magnetic resonance imaging in hemochromatosis: extrahepatic iron deposition.

The magnetic resonance (MR) appearance of the liver in hemochromatosis has been previously described. We report a case in which iron deposition in the pancreas, spleen, and lymph nodes is demonstrated by MR.

Magnetic resonance imaging of the pancreas with gadolinium-DTPA.

Gadolinium (Gd)-DTPA was evaluated as a contrast agent for magnetic resonance (MR) imaging of the pancreas at 1.5T. Twenty-five patients were imaged with identical gradient-echo (GE) (TR 47, TE 13, 80 degree pulse angle) and spin-echo (SE) (TR 300, TE 15) MR sequences prior to and following an intravenous bolus of 0.1 mmol/kg Gd-DTPA. Marked pancreatic enhancement was demonstrated on dynamic sequential breath-hold GE images obtained immediately following the Gd-DTPA bolus (116% mean enhancement over pre-Gd-DTPA images). Enhancement decreased but persisted on the SE images obtained approximately 5 and 15 min following the Gd-DTPA bolus (65 and 60% mean enhancement, respectively). Five of the patients had a pancreatic mass. In these five patients, the enhancement of pancreatic tissue resulted in improved conspicuity of the mass. These initial results suggest that pancreatic enhancement occurs following an intravenous bolus of Gd-DTPA and has the potential to improve MR visualization of pancreatic masses.

Biliary lithotripsy versus cholecystectomy: a cost-utility analysis.

Evaluating the economic impact of medical procedures is of increasing importance in the American health care system, and this is especially true in the case of new medical technologies. Both the cost and the outcome of a treatment, and its alternatives must be evaluated. A cost-utility analysis was performed to compare cholecystectomy with biliary lithotripsy accompanied by bile acid therapy. Using a Markov approach, a model was designed to project expected cost and quality-adjusted survival over a 5-year period in patients with solitary stones of less than or equal to 20 mm in diameter. The viewpoint of the analysis was chosen to be that of the general society, since it can be considered as a consensus of all interest groups. Direct costs were obtained from hospitals in Atlanta, Georgia; indirect costs are based on average United States earnings. Utility was estimated using a model that combines different scales of well-being with an underlying etiology. The findings indicate that from society's point of view for all patients meeting lithotripsy inclusion criteria, based on this cost-utility analysis, biliary lithotripsy would be the procedure of choice.

Splenic venous flow exceeding portal venous flow at Doppler sonography: relationship to portosystemic varices.

OBJECTIVE: The purpose of this study was to determine if the Doppler sonographic finding of hepatopetal flow in the splenic vein that exceeds hepatopetal flow in the portal vein is associated with portosystemic varices. MATERIALS AND METHODS: Sixty-four patients with chronic liver disease were studied retrospectively. In 32 patients, splenic venous flow exceeded portal venous flow (S > P group); in 32 patients, portal venous flow exceeded splenic venous flow (P > S group). All patients were evaluated with Doppler sonography and CT of the upper part of the abdomen. Upper endoscopy was performed within 3 months of sonography in 44 of the 64 patients. RESULTS: In the S > P group, mean splenic volume was significantly larger (p = .02) than in the other group. The prevalence of varices as determined by CT in the esophageal, coronary, and peripancreatic regions was also higher in this group (p < or = .01). When esophageal varices were present, they were judged on the basis of their CT appearance to be massive in 50% of the S > P group and in 0% of the P > S group. Upper endoscopy revealed esophageal varices in 92% of the S > P group and in 55% of the P > S group (p < .005). Bleeding esophageal varices were noted in 75% of the S > P group and in 30% of the P > S group (p < .01). CONCLUSION: Patients with chronic liver disease and the Doppler sonographic finding of splenic venous flow that exceeds portal venous flow have an increased prevalence of portosystemic varices, which tend to be larger and more likely to bleed.

Extravasation detection accessory: clinical evaluation in 500 patients.

PURPOSE: To assess the ability of an extravasation detection accessory (EDA) to detect clinically important (> or = 10 mL) extravascular injection of iodinated contrast material delivered with an automated power injector. MATERIALS AND METHODS: Five hundred patients referred for contrast material-enhanced body computed tomography (CT) participated in a prospective, multi-institutional, observational study in which the EDA was used to identify and interrupt any injection associated with clinically important extravasation. The presence or absence of extravasation was definitively established with helical CT at the injection site (injection rate, from 1.0 to 5.0 mL/sec; mean, 2.9 mL/sec; median, 3.0 mL/sec). RESULTS: There were four true-positive (extravasation volumes, 13-18 mL), 484 true-negative, 12 false-positive, and no false-negative cases. The prevalence of overall and clinically important (> or = 10 mL) extravasation was 3.6% (18 of 500 cases) and 0.8% (four of 500 cases), respectively. The EDA had a sensitivity of 100% (four of four cases; 95% CI: 51%, 100%) and a specificity of 98% (484 of 496 cases; 95% CI: 96%, 99%) in the detection of clinically important extravasation. CONCLUSION: The EDA is easy to use, safe, and accurate in the monitoring of intravenous injections for extravasation, which could prove especially useful in high-flow-rate CT applications.

Contrast-enhanced CT of the liver and spleen: comparison of ionic and nonionic contrast agents.

We conducted a randomized, blinded, prospective study evaluating hepatic parenchymal density changes during dynamic bolus CT (180 ml of contrast material given IV) and delayed CT (5 hr after 60 g of iodine) in order to compare the enhancement characteristics of an ionic contrast agent (iothalamate-60) and two nonionic agents (iohexol-300 and iopamidol-300). A total of 75 patients with known or suspected cancer were studied (25 patients per contrast agent). After a baseline unenhanced CT scan was obtained, dynamic bolus and delayed CT scans were obtained for all patients with one of the three contrast agents. The density of the liver and spleen was measured in Hounsfield units (H) for unenhanced CT, dynamic bolus CT, and delayed CT. The average percentage of enhancement was calculated as follows: postcontrast density minus precontrast density was divided by precontrast density and then multiplied by 100. For dynamic bolus CT, the average percentage of enhancement of the liver was 105% when iohexol-300 was used, 98% when iopamidol-300 was used, and 83% when iothalamate-60 was used. No significant difference was seen between the postcontrast enhancement of the three contrast agents on dynamic bolus CT scans (p greater than .05). For delayed CT, the average percentage of enhancement of the liver was 34% when iothalamate-60 was used, 28% when iopamidol-300 was used, and 16% when iohexol-300 was used. Both iothalamate-60 and iopamidol-300 showed superior enhancement on delayed CT, compared with iohexol-300 (p = .0001). We conclude that for dynamic bolus CT, all three contrast agents are similar, with no statistically significant differences in postcontrast enhancement of the liver. For delayed CT, however, hepatic enhancement with iothalamate-60 and iopamidol-300 is statistically superior to that with iohexol-300.

Hepatic tumors: comparison of CT during arterial portography, delayed CT, and MR imaging for preoperative evaluation.

Forty-three patients with known primary or secondary neoplastic involvement of the liver underwent evaluation to determine the number, size, and location of focal lesions before possible tumor resection. Imaging studies included computed tomography (CT) during arterial portography (CTAP), delayed CT, and magnetic resonance (MR) imaging at various pulse sequences. Results of radiologic studies were compared with surgical and pathologic findings. In the combined group of surgical and nonsurgical patients, CTAP was significantly more sensitive (85%) than all other techniques except 1.5-T T2-weighted spin-echo imaging (64%). Combining the information from all MR pulse sequences yielded a cumulative sensitivity of 68%. Combining the information from two modalities yielded sensitivity of 96% for CTAP plus MR imaging, 85% for CTAP plus delayed CT, and 77% for delayed CT plus MR imaging. The authors conclude that when it is vital to know the precise number, size, and location of focal hepatic lesions before tumor resection, CTAP has the highest sensitivity, but MR imaging is an important adjuvant.