Hepatic perfusion before and after the transjugular intrahepatic portosystemic shunt procedure: impact on survival

PURPOSE: This study correlates transjugular intrahepatic portosystemic shunt (TIPS) mortality with flow patterns in the cirrhotic liver. MATERIALS AND METHODS: Twenty-seven TIPS patients and 10 control subjects were used for this study. The authors evaluated hepatic perfusion with venous injections of Tc-99m pertechnetate before and after TIPS. Hepatic time-activity curves were analyzed for type and amount of liver perfusion. These parameters were correlated with survival for a mean follow-up of 18 months. RESULTS: The mean arterial contribution to liver blood flow was 25.4% in the normal control patients, 39.9% in patients prior to TIPS, and increased to 48.3% after TIPS. Although the proportion of arterial supply to the cirrhotic liver varied widely, TIPS mortality did not correlate with the preprocedure hepatic artery/portal venous perfusion ratio. However, patients with both an "arterialized" flow pattern and low total hepatic perfusion had higher mortality, with a mean survival of 2 months compared to patients with a more favorable perfusion profile (mean survival, 28.4 months). CONCLUSIONS: The proportion of arterial perfusion to the liver before TIPS did not affect survival. However, patients with a combination of reduced total hepatic perfusion and an arterial flow pattern had poorer survival, suggesting that both the quantity and quality of hepatic perfusion predicts TIPS outcome.     

Value of Doppler sonography in revealing transjugular intrahepatic portosystemic shunt malfunction: a 5-year experience in 216 patients

OBJECTIVE: The purpose of the study was to evaluate the long-term clinical efficacy of Doppler sonography in revealing failure of transjugular intrahepatic portosystemic shunts (TIPS). SUBJECTS AND METHODS: During a 5-year period, 1192 Doppler examinations were performed in 216 patients with TIPS. No regular follow-up shunt venography was performed. Doppler examinations were retrospectively compared with the results of shunt revisions. Sonograms with negative findings were compared with the patients' clinical status so that the number of false-negative sonographic findings leading to an episode of shunt failure (recurrence of gastrointestinal bleeding or ascites) could be ascertained. Sonographic parameters assessed included diameter, velocity, flow volume, and congestion index of the portal vein; and shunt velocities. RESULTS: Doppler sonography revealed shunt occlusion in 25 of 26 angiographically proven cases (sensitivity, 96%). The combination of velocity criteria (peak intrashunt velocity > or =250 cm/sec, maximum velocity in the portal third of the shunt < or =50 cm/sec, or maximum portal vein velocity less than or equal to two thirds of the baseline value) revealed shunt stenosis in 103 of 110 cases (sensitivity, 94%). Doppler sonography missed a significant shunt stenosis that led to an episode of gastrointestinal bleeding or ascites recurrence in only seven cases. The congestion index of the portal vein showed significant differences between patent and malfunctioning shunts (p < 0.001). CONCLUSION: Doppler sonography is an effective primary imaging method for long-term follow-up of patients with TIPS.     

Transjugular intrahepatic portosystemic shunt. Experiences at a liver transplantation center

Objective: Transjugular intrahepatic portosystemic shunt (TIPS) placement is an established therapy for portal hypertension that leads to variceal bleeding or refractory ascites. We present experiences of the role of TIPS at a liver transplantation center.Material and Methods: One hundred and ten patients were referred to the Radiological Department for TIPS placement. One of the 110 patients had recurrent cirrhosis after liver transplantation with refractory ascites. Function of the TIPS was controlled with Doppler US at 1 day, 1 week, 4 weeks and 4 months after TIPS placement and subsequently every 3 months. Shunt insufficiency was supposed when the blood flow velocity within the stent tract was under 50 cm/s and was an indication for TIPS revision.Results: TIPS was placed in 101 patients. After TIPS placement, 10 patients underwent liver transplantation. While waiting for the new liver, none of them developed variceal rebleeding, ascites or other complications of portal hypertension. Two of the 101 patients had episodes of rebleeding. The frequency of patients undergoing TIPS revision within the first year after TIPS placement was 67.5%, within the second year 38.0% and within the third year 24.4%. The revisions led to sufficient reduction of the portosystemic pressure gradient.Conclusion: In some liver transplant candidates, TIPS can be useful in minimizing the risk of complications of portal hypertension during the waiting time for a liver transplantation. TIPS can be monitored by Doppler US and revised if occlusion occurs.     

Value of hepatic angioscintigraphy combined to pulsed Echo-Doppler: application to the study of portal hypertension of cirrhotic patients. Apropos of 148 cases]

Quantitative hepatic angioscintigraphy was combined with duplex Doppler in order to study liver perfusion in normal subjects and in 148 patients with liver cirrhosis. The portal component of liver perfusion determined by scintigraphy was reduced in patients with liver cirrhosis and correlated to the development of cirrhosis and to porto-hepatic gradient pressure. Duplex Doppler allowed assessment of portal blood direction. Determination of portal blood flow was possible in only a few patients: portal blood flow was increased in the first stage of cirrhosis and then decreased; hepatofugal flow was observed only in the most severe stage. Angioscintigraphy and Duplex Doppler appear to be complementary in the study and follow-up of portal hypertension.     

Transjugular intrahepatic portosystemic shunt in a patient with cavernomatous portal vein occlusion

A 23-year-old woman with liver cirrhosis secondary to primary sclerosing cholangitis was referred to us for the treatment of recurrent bleeding from esophageal varices that had been refractory to endoscopic sclerotherapy. Her portal vein was occluded, associated with cavernous transformation. A transjugular intrahepatic portosystemic shunt (TIPS) was performed after a preprocedural three-dimensional computed tomographic angiography evaluation to determine feasibility. The portal vein system was recanalized and portal blood flow increased markedly after TIPS. Esophageal varices disappeared 3 weeks after TIPS. Re-bleeding and hepatic encephalopathy were absent for 3 years after the procedure. We conclude that with adequate preprocedural evaluation, TIPS can be performed safely even in patients with portal vein occlusion associated with cavernous transformation.     

Quantitative evaluation of the hepatic functional reserve using technetium-99m DTPA-galactosyl human serum albumin before and after transjugular intrahepatic portosystemic shunt

Transjugular intrahepatic portosystemic shunt (TIPS), a new therapeutic method, has been performed widely for the treatment of portal hypertension. TIPS produces a decrease in the portal blood flow to the hepatic parenchyma, which is considered to cause a reduction in hepatic functional reserve. To evaluate the changes in hepatic functional reserve after TIPS, we performed technetium-99m DTPA-galactosyl human serum algumin (^99mTc-GSA) hepatic scintigraphy before and after TIPS in eight male patients, ranging in age from 54 to 72 years (mean 62.2 years). Two quantitative indices – blood clearance index (uptake ratio of the heart at 15 min to that at 3 min, HH15) and hepatic accumulation index (uptake ratio of the liver to the liver plus heart at 15 min, LHL15) – were calculated from the time-activity curves of the heart and liver. Early and late uptake constant indices (early and late KU) were also calculated from the time-activity curves of the heart and liver by means of Patlak plot. The values of HH15, LHL15 and late KU deteriorated after TIPS in all patients. Early KU (1–3 min) decreased by more than 55% in two patients who showed a poor prognosis and corresponded well with the status of the portosystemic shunt. It is concluded that ^99mTc-GSA hepatic scintigraphy is a useful means of evaluating the degree to which hepatic function is compromised following TIPS. The post-TIPS alterations in HH15, LHL15 and late KU (5–10 min) reflect the changes in hepatic functional reserve, and early KU is a useful index for evaluating the degree of portosystemic shunt. Received 8 April and in revised form 16 June 1997     

Perfusion imaging of the liver: current challenges and future goals

Improved therapeutic options for hepatocellular carcinoma and metastatic disease place greater demands on diagnostic and surveillance tests for liver disease. Existing diagnostic imaging techniques provide limited evaluation of tissue characteristics beyond morphology; perfusion imaging of the liver has potential to improve this shortcoming. The ability to resolve hepatic arterial and portal venous components of blood flow on a global and regional basis constitutes the primary goal of liver perfusion imaging. Earlier detection of primary and metastatic hepatic malignancies and cirrhosis may be possible on the basis of relative increases in hepatic arterial blood flow associated with these diseases. To date, liver flow scintigraphy and flow quantification at Doppler ultrasonography have focused on characterization of global abnormalities. Computed tomography (CT) and magnetic resonance (MR) imaging can provide regional and global parameters, a critical goal for tumor surveillance. Several challenges remain: reduced radiation doses associated with CT perfusion imaging, improved spatial and temporal resolution at MR imaging, accurate quantification of tissue contrast material at MR imaging, and validation of parameters obtained from fitting enhancement curves to biokinetic models, applicable to all perfusion methods. Continued progress in this new field of liver imaging may have profound implications for large patient groups at risk for liver disease.     

Early sonographic evaluation of the transjugular intrahepatic portosystemic shunt (TIPS)

The purpose of this study was to evaluate duplex and color Doppler findings in patients before and within 24 h after transjugular intrahepatic porto-systemic shunts (TIPS). Conventional duplex and color Doppler were used in the assessment of 19 patients who underwent TIPS as part of a prospective protocol. Patients were examined within 24 h before and after the procedure. Before TIPS, patency, flow direction, and peak flow velocity in the main portal vein and hepatic artery were studied, as well as patency and flow direction in hepatic veins, splenic vein, and inferior vena cava (IVC). Immediately after the procedure, sonographic identification of stent position, shunt patency, and flow dynamics were evaluated and patency and flow direction of hepatic veins, splenic vein, and IVC were determined. The portogram performed at the end of the procedure was compared with the 24-h sonographic studies after TIPS to determined sonographic/angiographic correlation. No intraparenchymal abnormalities or perihepatic fluid collections were detected after the procedure. The metallic stent was clearly seen in all patients. Mean peak shunt flow velocities were 139±50 cm/sec within 24 h after TIPS. Absence of flow through the shunt was correctly identified in one case and confirmed angiographically. Mean peak flow velocity in the portal vein before TIPS was 22±13.6 cm/sec and increased to 43.6±9.1 cm/sec after TIPS (p<0.05). The hepatic artery peak systolic velocity increased from 77±51 cm/sec before TIPS to 119±53 cm/sec after the procedure (p=0.029). Conventional duplex and color Doppler ultrasound proved to be a useful non-invasive diagnostic method to assess patients who have undergone TIPS. We propose its use as the primary diagnostic modality in these patients.     

Refractory hepatic encephalopathy due to concomitant transjugular intrahepatic portosystemic shunt and spontaneous mesocaval shunt controlled by embolization of the competitive portosystemic shunt

Spontaneous mesocaval shunt (SMCS) is an uncommon cause of refractory encephalopathy after transjugular intrahepatic portosystemic shunt (TIPS) creation. We report a patient who presented with refractory hepatic encephalopathy (HE) post-TIPS creation for variceal bleeding in whom a SMCS was found. Percutaneous transhepatic occlusion of the SMCS reduced the portal vein flow diverted from the liver and provided sufficient liver perfusion to reverse the HE while maintaining satisfactory decompression of esophageal varices.     

Changes in the distribution of hepatic arterial blood flow following TIPS with uncovered stent and stent-graft: an experimental study

Purpose: To evaluate changes in distribution of hepatic arterial blood flow in the liver following insertion of an uncovered stent and subsequently a stent-graft in the transjugular intrahepatic portosystemic shunt (TIPS) channel. Methods: The experiments were performed in eight healthy pigs under general anesthesia. In a pilot study in one pig, scintigraphic evaluation of arterial perfusion to the liver was done before and after inflation of a balloon in the right hepatic vein. In the other pigs, outflow from the right liver vein was checked repeatedly by contrast injection through a percutaneously inserted catheter. The arterial perfusion through the liver was examined by scintigraphy, following selective injection of macro-aggregate of 99Tc m-labeled human serum albumin 99Tc m-HSA) into the hepatic artery. This examination was done before and after creation of a TIPS with an uncovered stent and subsequently after insertion of a covered stent-graft into the cranial portion of the shunt channel. Results: In the pilot study changes in the arterial perfusion to the liver were easily detectable by scintigraphy. One pig died during the procedure and another pig was excluded due to dislodgement of the hepatic artery catheter. The inserted covered stent obstructed venous outflow from part of the right liver lobe. The 99Tc m-HSA activity in this part remained unchanged after TIPS creation with an uncovered stent. A reduction in activity was seen after insertion of a stent-graft (p= 0.06). Conclusion: The distribution of the hepatic arterial blood flow is affected by creation of a TIPS with a stent-graft, in the experimental pig model.     

Hepatic perfusion as a predictor of mortality after transjugular intrahepatic portosystemic shunt creation in patients with refractory ascites

PURPOSE: To determine whether hepatic perfusion patterns predict mortality after transjugular intrahepatic portosystemic shunt (TIPS) creation in patients with severe ascites. MATERIALS AND METHODS: This retrospective study included 22 patients who had enhanced cine magnetic resonance (MR) imaging performed immediately before TIPS creation in the angled coronal plane including the left kidney, liver, and main portal vein. Regions of interest were centered over the liver and kidney, and perfusion curves were generated and reviewed before the standard TIPS procedure was performed. Four patients did not undergo TIPS creation as a result of very poor hepatic perfusion by MR. All patients were followed clinically and by ultrasound surveillance of their shunt. RESULTS: Eleven patients died within 6 months, including all four patients who did not have a TIPS because of MR evidence of poor hepatic perfusion. Of these 11 patients, eight (73%) had unfavorable liver flow consisting of diminished enhancement compared to the kidney and early peak enhancement of less than 50 seconds. The surviving patients all showed a delayed peak enhancement of greater than 50 seconds. CONCLUSIONS: In patients undergoing TIPS creation for refractory ascites, blunted arterial-type hepatic enhancement is a poor prognostic sign. Cine MR imaging with evaluation of hepatic perfusion can be performed and reviewed before the TIPS procedure. Alternative techniques for ascites reduction may be preferred for patients with unfavorable hepatic perfusion.     

Portal flow and arterioportal shunting after transjugular intrahepatic portosystemic shunt creation

PURPOSE: It was postulated that a transjugular intrahepatic portosystemic shunt (TIPS) produces arterioportal shunting and accounts for reversed flow in the intrahepatic portal veins (PVs) after creation of the TIPS. This study sought to quantify this shunting in patients undergoing TIPS creation and/or revision with use of a direct catheter-based technique and by measuring changes in blood oxygenation within the TIPS and the PV. MATERIALS AND METHODS: This prospective study consisted of 26 patients. Median Model for End-stage Liver Disease and Child-Pugh scores were 13 and 9, respectively. Primary TIPS creation was attempted in 21 patients and revision of failing TIPS was undertaken in five. In two patients, TIPS creation was unsuccessful. All TIPS creation procedures but one were performed with use of polytetrafluoroethylene-covered stent-grafts. Flow within the main PV (Q(portal)) was measured with use of a retrograde thermodilutional catheter before and after TIPS creation/revision, and TIPS flow (Q(TIPS)) was measured at procedure completion. The amount of arterioportal shunting was assumed to be the increase between final Q(portal) and Q(TIPS), assuming Q(TIPS) was equivalent to the final Q(portal) plus the reversed flow in the right and left PVs. Oxygen saturation within the TIPS and the PV was determined from samples obtained during TIPS creation and revision. RESULTS: Mean Q(portal) before TIPS creation was 691 mL/min; mean Q(portal) after TIPS creation was 1,136 mL/min, representing a 64% increase (P = .049). Mean Q(TIPS) was 1,631 mL/min, a 44% increase from final Q(portal) (P = .0009). Among cases of revision, baseline Q(portal) was 1,010 mL/min and mean Q(portal) after TIPS revision was 1,415 mL/min, a 40% increase. Mean Q(TIPS) was 1,693 mL/min, a 20% increase from final Q(portal) (P = .42). Arterioportal shunting rates were 494 mL/min after TIPS creation and 277 mL/min after TIPS revision, representing 30% of total Q(TIPS) after TIPS creation and 16% of Q(TIPS) after TIPS revision. No increase in oxygen tension or saturation was seen in the PV or TIPS compared with initial PV levels. Q(TIPS) did not correlate with the portosystemic gradient. CONCLUSION: TIPS creation results in significant arterioportal shunting, with less arterioportal shunting seen among patients who undergo TIPS revision. Further work is necessary to correlate Q(TIPS) with the risk of hepatic encephalopathy and liver failure.     

经肝段下腔静脉建立TIPS分流道的初步临床结果

目的 评估经肝段下腔静脉TIPS分流术在肝静脉与门静脉间解剖异常时操作的可行性，讨论其临床意义。方法 65例肝硬变门静脉高压患者行经肝段下腔静脉直接穿刺门静脉完成TIPS分流术。结果 65经肝段下腔静脉TIPS分流术均获成功，技术成功率100％，未出现术中技术相关并发症，一年内再狭窄率明显低于常规TIPS，3例肝性脑病经限流支架置入得以控制。结论 经肝段下腔静脉TIPS分流术技术用于肝静脉与门静脉间解剖异常病例是安全有效的，同时提示由于肝内分流道曲度较小，一年内支架开通率明显提高。     

Comparison of pulsed Doppler sonography and angiography in patients with portal hypertension

Pulsed Doppler sonography and liver panangiography were performed in 43 patients with cirrhosis. Fourteen patients were evaluated preoperatively, and 28 patients were evaluated after a variceal decompressive shunt. One patient was studied before and after undergoing a shunt. The direction of portal blood flow by Doppler sonography was compared with both the grading pattern and direction of flow by angiography. When portal blood flow was determined to be antegrade by Doppler sonography, angiography showed antegrade flow in 84% (grade I, II, or III portal venous pattern). Six percent had retrograde flow (grade IV), and 10% had portal vein thrombosis. When the portal blood flow was determined to be retrograde by Doppler sonography, angiography showed retrograde flow (grade IV portal venous pattern) in 80% and antegrade flow (grade I, II, or III) in 20%. When an inadequate Doppler tracing was obtained from the portal vein, angiography showed either grade I, II, or III in 38%; grade IV in 50%, and portal vein thrombosis in 13%. There was poor correlation between the calculated mean flow rates, as determined by Doppler sonography, and the angiographic grade. We conclude that pulsed Doppler sonography is accurate in determining the direction of portal flow when an adequate tracing is obtained (36 of 44 studies). When an inadequate tracing is obtained, retrograde portal flow or portal vein thrombosis is likely.     

Color Doppler sonography of the hepatic artery and portal venous system

Color Doppler sonography is an important noninvasive diagnostic tool for detecting abnormalities of the hepatic vasculature in patients with diffuse liver disease. To study its usefulness in these cases, we retrospectively reviewed the findings in 147 patients with abnormal portal venous color Doppler sonograms. This group comprised all patients with abnormal portal venous color Doppler sonograms studied from February 1987 to July 1989. Correlative imaging was not available in all cases. The sonographic diagnoses included (1) portal venous thrombosis (50 patients, 93 vessels); (2) portal-systemic or portal-portal collaterals (80 patients, 95 collaterals); (3) reversed, bidirectional, or other abnormal portal venous flow patterns (36 patients); and (4) abnormal hepatic arterial flow (20 patients). Since the results reported derive from a retrospective review without consistent correlation with other imaging studies, no appraisal of the sensitivity or accuracy of portal color Doppler sonography could be made from our data. The ability of color Doppler sonography to visualize flow without altering hemodynamics has led to several novel observations in these patients. These include increased arterial flow in states of low portal blood flow, reversal of portal flow direction postprandially, coincident reversed and hepatopetal flow in different branches of a single portal vein, and normal helical portal venous flow. These and other findings show that color Doppler sonography has enhanced our ability to detect abnormalities of the hepatic and portal venous system.     

经颈静脉肝内门-体静脉分流术应用疗效观察

本文报告经颈静脉肝内门-体静脉分流术(TIPSS)14例,成功12例。术后食道静脉曲张明显减轻乃至消失、门脉主干血流速度显著增加、门脉压力平均下降1.48kPa、血小板有所升高、白细胞变化不大、脾脏体积缩小30-60％。本组临床应用结果表明:TIPSS创伤性小,降低门脉压可靠,是治疗门脉高压症的有效方法;此技术成功的关键是术前了解肝静脉与门静脉的空间关系。     

Prevention of hepatic infarction as acute-phase complication of TIPS by temporary balloon occlusion in a patient with primary myelofibrosis

Severe acute liver dysfunction occurred following transjugular intrahepatic portosystemic shunt (TIPS) creation in a patient with massive ascites due to portal hypertension associated with primary myelofibrosis. On US and TIPS venography, we considered that the acute liver ischemia was induced by TIPS. To avoid diffuse hepatic infarction and irreversible liver damage, a balloon catheter was inserted transjugularly into the TIPS tract and occluded it to increase portal venous flow toward the peripheral liver parenchyma. The laboratory data indicating hepatic dysfunction were improved after the procedure. We should pay attention to the possible occurrence of acute hepatic ischemia and infarction after TIPS creation even in a case of noncirrhotic portal hypertension. In such cases, temporary balloon occlusion of TIPS is an effective therapeutic method, probably as a result of inducing the development of arterial compensation through the peribiliary plexus.     

Inadvertent arteriovenous stenting during transjugular intrahepatic portosystemic shunt procedure and the importance of hepatic artery perfusion

Penetrating the hepatic artery during transjugular intrahepatic portosystemic shunt (TIPS) is a relatively frequent but almost always benign complication. We report a patient in whom the right hepatic artery, originating from the superior mesenteric artery, was inadvertently catheterized and stented. The arteriovenous fistula was treated with a detachable balloon positioned within the hepatic artery. A second TIPS was attempted and successfully created during the same session. The patient died of cardiac failure, attributed to rapid resolution of massive ascites after TIPS with circulatory overload. At autopsy, the liver distal to the arterial occlusion balloon was infarcted, illustrating the importance of hepatic artery perfusion in liver cirrhosis.     

Effects of TIPS on liver perfusion measured by dynamic CT

OBJECTIVE: Our aim was to measure the arterial, portal venous, and total perfusion of the liver parenchyma with dynamic, single-section CT in patients with liver cirrhosis before and after transjugular intrahepatic portosystemic shunt (TIPS) placement and to compare the results with normal values. SUBJECTS AND METHODS: Perfusion of the liver parenchyma was measured in 24 healthy volunteers and 41 patients with liver cirrhosis using dynamic single-section CT. Seventeen patients underwent TIPS placement, and CT measurements were repeated within 7 days. CT scans were obtained at a single level comprising the liver, spleen, aorta, and portal vein. Scans were obtained over a period of 88 sec (one baseline scan followed by 16 scans every 2 sec and eight scans every 7 sec) beginning with the injection of a contrast agent bolus (40 mL at 10 mL/sec). Parenchymal and vascular contrast enhancement was measured with regions of interest, and time-density curves were obtained. These data were processed with a pharmaco-dynamic fitting program (TopFit), and the arterial and portal venous component and the total perfusion of the hepatic parenchyma were calculated (milliliters of perfusion per minute per 100 mL of tissue). RESULTS: Mean normal values for hepatic arterial, portal venous, and total perfusion were 20, 102, and 122 mL/min per 100 mL, respectively. In patients with cirrhosis before TIPS, mean hepatic arterial, portal venous, and total perfusion was 28, 63, and 91 mL/min per 100 mL, respectively, which was statistically significant for all values (p <0.05). After TIPS, hepatic perfusion increased to a mean value of 48, 65, 113 mL/min per 100 mL for arterial (p <0.01), portal venous, and total (p=0.011) perfusion, respectively. CONCLUSION: In patients with cirrhosis, the hepatic arterial perfusion increased, whereas portal venous and total perfusion decreased compared with that of healthy volunteers. TIPS placement caused a statistically significant increase of the hepatic arterial and total hepatic perfusion. The portal venous parenchymal perfusion remained unchanged.     

多普勒导丝评价TIPS术门腔分流道血流特点

目的应用血管内多普勒导丝测定TIPS术后门腔分流量及血流特点,提出一种新的、更可靠的检测静脉血流动力学指标的方法。方法 10例门静脉高压患者TIPS术后即刻,使用血管内多普勒导丝测定分流通道内血流速度,结合DSA技术,测出血流量;并予10例正常肝静脉血流作为对照。结果测得TIPS术后分流通道内的平均峰值流速(APV)为(18.51±7.32)cm/s,最大峰值流速(MPV)为(25.93±9.54)cm/s,分流道的直径为(0.80±0.26)cm,门腔分流量为(557.96±94.57)ml/min,并且获得血流频谱特点为波形呈单相,不随心动周期而变化。而肝静脉APV为(15.73±4.52)cm/s;MPV为(26.01±8.33)cm/s;血流量为(654.64±108.56)ml/min,血流频谱特点为波形呈三相,随心动周期而变化。结论利用血管内多普勒导丝能准确而方便地测出TIPS术后门腔分流量并用于评价其血流特点,为检测静脉血流提供了一种新的方法,具有实用性及可行性。