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MR imaging of liver

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MR imaging protocols,indications and imaging features of diffuse and focal liver diseases

MR imaging protocols,indications and imaging features of diffuse and focal liver diseases

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  • 1. MRI OF LIVER Dr.Parvathy S Nair
  • 2. Role of MRI in liver imaging • Suspected Liver Metastases – CT is the imaging modality of choice – Diffuse liver disease and fatty infiltration limit the sensitivity of CT in lesion detection. If the clinical suspicion of a lesion is high and the CT scan is negative –MR • Preoperative Evaluation of Liver Tumors – Contrast-enhanced MRI is superior to CT - high sensitivity for detecting small lesions and its ability to characterize small lesions. – Tissue characterization with T1- and T2-weighted images, a high spatial resolution, and a high sensitivity for contrast enhancement contribute to the greater accuracy
  • 3. • Screening for Liver Tumors in Diffuse Hepatic Disease – US can be used for initial screening, CT or MRI should be used once cirrhosis sets in. – In patients with equivocal findings on CT, MRI is useful for its ability to accurately identify fatty infiltration and small HCCs • Incidentally Detected Lesions with Other Imaging Modalities • Assessing Tumor Response to Surgery or Chemotherapy – The presence of enhancement along surgical margins usually represents postoperative changes, but nodular enhancement or a discrete soft-tissue mass at the surgical margins indicates recurrence.
  • 4. • A comprehensive MR imaging examination of the liver should include T1-weighted images,T2-weighted images and dynamic multiphasic contrast-enhanced images, preferably supplemented by chemical-shift images and fat-saturation images.
  • 5. • Single-shot fast-spin echo (SSFSE) is recommended for coronal localizer imagesHASTE • Each of the images is obtained in <1 second, providing a rapid, motion-independent T2weighted survey. • These sequences give an overview of the liver, and differentiate solid lesions from cystic lesions or hemangiomas, particularly with the use of a heavily T2-weighted sequence
  • 6. • Gradient-echo sequences are generally used for T1-weighted sequences. • Spoiled gradient-echo (SGE) sequences allow acquisition of sufficient sections in one breath hold (about 20 sec) for complete liver coverage and provide good SNR– FLASH • Short tau inversion recovery (STIR) also may be used to acquire T2WI – these images have high soft-tissue contrast and minimal signal from adipose tissue.
  • 7. Dual Gradient-Echo In-Phase and Opposed-Phase • This sequence is primarily used to detect and characterize focal as well as diffuse steatosis of the liver by using the chemical shift cancellation artifact (also known as fat-water cancellation artifact, black lining artifact, or India ink artifact).
  • 8. • Protons in water and fat precess at different frequencies. • Chemical shift • At certain TE they are in-phase and at other TE they are out of phase • In phase TE images will have signals of water and fat added together-both are bright • Out of phase-fat is subtracted. • In out of phase imaging fat containing lesions will appear darker when compared to in-phase. • Only when the lesions contain both fat and water.
  • 9. • The characterization of primary focal liver lesions such as hepatocellular carcinoma and adenoma can be improved by using the chemical shift cancellation artifact . • These lesions may contain fat and water within the same voxel, which can be detected reliably with gradient-echo in- and opposedphase MR imaging.
  • 10. CONTRAST STUDIES Post-contrast • T1 2D or 3D gradient echo sequences (e.g. VIBE) at – arterial phase : 20 - 25 seconds – portal venous phase : 60 - 70 seconds – equilibrium phase : 3 - 5 minutes – hepatobiliary delayed phase : 10 - 30 minutes with and without fat sat
  • 11. Contrast Agents • Extracellular agents • Reticuloendothelial agents • Hepatobiliary agents • Blood pool agents • Combined agents
  • 12. Extracellular agents • Extracellular agents are distributed within the extracellular interstitial space. • Indications – Lesion detection – Lesion characterization – Liver vasculature assessment.
  • 13. • Gadolinium has seven unpaired electrons and is highly paramagnetic. • Gadolinium shortens the T1 (spin-lattice) and T2 (spinspin) relaxation times of adjacent water protons. • These relaxation effects tend to cause signal enhancement at T1-weighted imaging and signal loss at T2-weighted imaging • Appropriate evaluation of the liver requires imaging during the arterial phase of extra-cellular contrast enhancement, specifically the late hepatic arterial phase, when the portal vein is only slightly enhanced
  • 14. Reticuloendothelial Agents • Reticuloendothelial agents target the reticuloendothelial system, particularly the liver and spleen. • Reflects the number of functioning macrophages • Currently in clinical use include superparamagnetic iron oxide (SPIO) particles.
  • 15. • SPIO particles are phagocytosed by macrophages throughout the body but are preferentially entrapped by Kupffer cells, which line the hepatic sinusoids. • SPIO particles act as a negative contrast agent. Their superparamagnetic properties cause local magnetic field inhomogeneity and result in considerable T2 and T2* shortening. • Tissues that accumulate SPIO particles thus show reduced signal intensity, particularly on T2- and T2*-weighted images, and to a lesser extent on T1-weighted images
  • 16. • Most liver tumors—whether benign or malignant, primary or metastatic—are deficient in Kupffer cells and do not exhibit SPIO particle uptake • Thus, after an infusion of SPIO particles, – Liver becoes preferentially darker – Tumors become relatively hyperintense • The primary exception to this rule occurs in focal nodular hyperplasia, in which SPIO particles may accumulate, with a resultant isointense or even hypointense appearance of lesions in comparison with the normal liver parenchyma
  • 17. Axial T1-weighted spo image, obtained after injection of SPIO partic before that of gadolini shows negative enhan of the background live and clearly depicts the (arrow). Axial T1-weighted spoiled GRE image, obtained during the late hepatic arterial phase of enhancement after the administration of SPIO particles and gadolinium, shows increased conspicuity of the lesion (arrow).
  • 18. • SPIO particles are most useful when combined with gadolinium to create a double-contrast effect. • With this technique, the SPIO particles are infused first and are followed later by gadolinium. • The two agents synergistically improve lesionto-liver contrast on dynamic T1- images because the background liver is darkened by the SPIO particles while the lesion of interest is lightened by gadolinium
  • 19. Negative contrast enhancement effect of SPIO particles in a 56-year-old man with cirrhosis and HCC.
  • 20. • Because mangafodipir is taken up only by hepatocytes, hepatocyte-containing masses (eg, HCC, focal nodular hyperplasia, and hepatic adenoma) appear enhanced in 75% of cases, whereas metastases generally are not enhanced
  • 21. MRI in Diffuse Liver Diseases • Homogenous- involves disorders of hepatocytes and reticuloendothelial cells – Hemochromatosis,steatosis • Segmental- segmental fatty liver and focal confluent segmental fibrosis – subacute hepatitis – Fatty liver
  • 22. • Nodular- multiple abnormal nodular intensities- includes disorders that cause numerous nodular lesions corresponding to iron deposits in regenerative nodules or granulomas – cirrhosis, Wilson's disease, and sarcoidosis • Perivascular involve the periportal lymphatic channel and Glisson's capsules congestive liver and Budd-Chiari syndrome are usually associated with periportal high signal intensity of the liver.
  • 23. DIFFUSE HOMOGENOUS DISTRIBUTION Hemochromatosis • Hemochromatosis is an iron overload disorder resulting in hepatic parenchymal or reticuloendothelial deposition of iron. • On T2WI, the superparamagnetic effect of iron causes decreased signal intensity of liver parenchyma in comparison with that of the paraspinal muscle • Gradient-echo T2* WI are more sensitive to magnetic susceptibility effects. T1WI also show decreased signal intensity of liver parenchyma
  • 24. T2-weighted MR image shows decreased signal intensity of liver, pancreas, and spleen when compared with that of paraspinal muscle.
  • 25. Steatohepatitis • Pathologically, steatohepatitis demonstrates varying degrees of steatosis (fatty liver), mixed cellular inflammatory infiltrate across the lobule, the presence of hepatocyte injury, and fibrosis. • This condition is unrelated to alcohol abuse. • Radiologically, steatohepatitis cannot be reliably distinguished from other causes of fatty liver. • The presence of >33% fat on liver biopsy was shown to be optimal for detecting steatosis on radiological imaging • Nonalcoholic steatohepatitis is sometimes associated with acute hepatic failure, and in a minority of patients, the disease progresses to cirrhosis.
  • 26. • MR images• diffuse homogeneous increased signal intensity on in-phase images and • diffuse homogeneous low signal intensities on opposed-phase T1-weighted images
  • 27. Glycogen Storage Diseases • Patients with this disease may also have hepatocellular adenoma, manifesting as a lowattenuation tumor on conventional CT images and as hyperintensity on T1- and T2-weighted MR images
  • 28. 36-year-old man with glycogen storage disease. T1weighted spin-echo MR image shows low signal intensity of normal hepatic parenchyma compared with that of bone marrow.
  • 29. Glycogen storage disease. T1-weighted spinecho MR image reveals homogeneously increased signal intensity of hepatic parenchyma compared with that of bone marrow. Note round high-signal-intensity tumor (arrow) in lateral segment. T2-weighted spin-echo MR image shows tumor with high signal intensity
  • 30. SEGMENTAL DISTRIBUTION Fatty Liver • Fatty change in hepatocytes occurs in patients with diabetes mellitus, obesity, transplanted liver, alcohol abuse, and chemical toxicity. • Segmental fatty liver is characterized by segmental distribution of fatty infiltration, depending on regional differences in perfusion. • T1-weighted spin-echo MR images show slightly increased signal intensity resulting from fatty infiltration. • In-phase MR images show similar intensity for normal liver parenchyma and fatty changes. • Opposed-phase T1-weighted MR images are the most useful for detecting low signal intensity caused by fatty change.
  • 31. Normal Liver Fatty Liver
  • 32. Subacute Hepatitis • Subacute hepatitis is caused primarily by viral infection, such as hepatitis B or C, or by drug use. • When the liver is severely damaged, parenchymal intensity is reduced on T1-weighted MR images and increased on T2-weighted MR images. • Segmental atrophy may manifest as abnormal signal intensity (i.e., areas of focal confluent fibrosis with abnormal signal intensity and abnormal enhancement)
  • 33. T1-weighted MR image reveals diffuse atrophy of liver with irregular surface and decreased signal intensity of left lobe (arrows). T2-weighted MR image shows segmental increase in signal intensity of left lobe Post contrast gradient-echo T1-weighted MR image -segmental delayed enhanced area probably corresponding to segmental fibrosis.
  • 34. NODULAR DISTRIBUTION Liver Cirrhosis • Cirrhosis, the chronic response to repeated episodes of hepatocellular injury, is characterized by regeneration and fibrosis. • Common causes of cirrhosis include alcoholism and viral infections such as hepatitis B and C. • The role of imaging in cirrhosis is the early detection of HCC and the differentiation of regenerative nodules from dysplastic nodules and HCC. • Regenerative changes caused by cirrhosis appear throughout the liver as small round masslike structures. • These lesions appear as hypointense nodules on T2-weighted MR images, are most apparent on gradient-echo images, and are believed to be caused by deposition of hemosiderin in the regenerative nodules.
  • 35. T2-weighted MR image reveals multiple regenerative nodules with low signal intensity
  • 36. Wilson's Disease • In patients with Wilson's disease the biliary excretion of copper is impaired, resulting in the accumulation of toxic levels of copper in the liver, brain, and cornea. • Copper has no ferromagnetic effect on MR imaging because copper in hepatocytes may combine with proteins. • The most common finding of Wilson's disease is cirrhotic change. • Iron in regenerative nodules causes numerous small nodular intensities scattered throughout the liver on T2weighted MR images.
  • 37. T2-weighted spin-echo MR image shows numerous small low-signal-intensity nodules scattered throughout liver, probably corresponding to iron in regenerative nodules
  • 38. Sarcoidosis • Sarcoidosis, a common systemic granulomatous disease, occasionally involves the liver, spleen, and subdiaphragmatic lymph nodes. • Noncaseating epithelioid granulomas with surrounding fibrosis are present in the periportal region and portal tracts • T2-weighted MR images shows liver lesions as numerous areas of low signal intensity and faint patchy high-signal-intensity structures that corresponds to the enhanced areas seen on contrast-enhanced T1weighted images. • Such intensities may correspond histologically to granulomas with surrounding fibrosis.
  • 39. T2-weighted MR image shows faint patchy or geographic high-signal-intensity lesions (large arrows) in liver. Numerous small low-signalintensity nodules (small arrows) are also seen. Gadolinium-enhanced gradient-echo T1weighted MR image reveals patchy or geographically enhanced area
  • 40. Congested Liver Congested liver is a common complication of congestive heart failure, constrictive pericarditis, and right-sided heart failure resulting from pulmonary artery obstruction caused by lung cancer. T2-weighted MR images of patients with congested liver show periportal hyperintensity and prominent perivascular zones of diminished attenuation resulting from presumed perivascular lymphedema
  • 41. MRI in focal liver lesions Simple hepatic cyst. Axial contrastenhanced 3D GRE T1-weighted VIBE MR image shows a simple cyst (arrow) with the typical features of nonenhancement and low signal intensity.
  • 42. Hepatic cysts in a patient with Caroli disease. Axial contrast-enhanced 3D VIBE MR image shows cystic dilatation of the biliary ducts manifesting as multiple small, nonenhancing cysts. Note the presence of the “central dot sign” (arrow).
  • 43. Regenerating Nodules The lesions exhibit low signal intensity on both images and no enhancement after contrast material injection.
  • 44. Hemangioma • A hepatic haemangioma is a benign hypervascular liver lesion. It is the most common benign tumour of the liver, and the most common liver tumour overall • Blood supply is predominantly hepatic arterial
  • 45. MRI • T1 - hypointense relative to liver parenchyma • T2 - intensely hyperintense relative to liver parenchyma • T1 C + (Gd) - often shows peripheral nodular enhancement which progresses centripetally (inward) on delayed images. – haemangiomas tend to retain contrast on delayed (>5 minute) contrast-enhanced images. – atypical haemangiomas may demonstrate slightly altered enhancement patterns. – in general delayed (1 hour) imaging may not be helpful, since haemangiomas can have a variable appearance that ranges from hypointensity to diffuse and central enhancement.
  • 46. PORTAL VENOUS PHASE A hepatic hemangioma with the typical findings of early peripheral nodular enhancement and progressive centripetal filling. These findings helped confirm the diagnosis. DELAYED PHASE
  • 47. Dysplastic Nodule • A dysplastic nodule is defined as a small cluster of hepatocytes with dysplasia indicating the presence of nuclear and cytoplasmic changes but without definite histologic criteria for malignancy. • Premalignant. • Variable MR appearance • Generally hypointense or, more commonly, hyperintense on T1-weighted images and iso- or hypointense on T2weighted images, without prominent arterial phase enhancement after contrast material administration. • Dysplastic nodules are almost never hyperintense on T2weighted images
  • 48. Axial unenhanced and contrast-enhanced 3D GRE T1-weighted VIBE MR images The lesions exhibit high signal intensity on both images and no enhancement after contrast material administration.
  • 49. Hepatic adenoma • Hepatic adenoma is a focal benign proliferation of hepatocytes within an otherwise normal liver. • MR imaging appearance of hepatic adenomas ranges from mildly hypointense to hyperintense on T1weighted images. • The high signal intensity is due to the presence of fat or blood products. • On T2-weighted images, hepatic adenomas have a nonspecific, heterogeneous, slightly hyperintense appearance. • Immediate enhancement is seen on arterial phase images after intravenous gadolinium chelate administration but rapidly fades to near isointensity on subsequent images
  • 50. An adenoma (white arrow) with typical immediate enhancement. Note also the focal area of hemorrhage (black arrow).
  • 51. Focal Nodular Hyperplasia • Common benign tumor • The origin of FNH is thought to be due to hyperplastic growth of normal hepatocytes with a malformed biliary draining system. • Macroscopically, typical lesions demonstrate a tumour which is often quite large with well marginated margins. • A prominent central scar is usually noted with radiating fibrous septae : <50% of cases. • A large central artery is usually present with spoke-wheel like centrifugal flow(no portal veins). • Kupffer cells are present
  • 52. MRI is both sensitive (70%) and specific (98%). • T1 – iso to somewhat hypo intense – hypo intense central scar • T2 – iso to somewhat hyperintense – hyperintense central scar • T1 C+ (Gd) : – gadolinium enhancement is similar to CT intense early arterial phase enhancement – iso intense to liver on portal venous phase – central scar retains contrast on delayed scans • T1 C+ (hepatobilliary contrast) : demonstrates enhancement
  • 53. High T2 signal intensity with immediate lesion enhancement, poor enhancement of the central scar on the early phase image and increased enhancement of the scar on the delayed phase image
  • 54. Hepatocellular Carcinoma • T1 – variable – iso or hyperintense compared to liver – hyperintensity may be due to • intratumoural fat • decreased intensity in surrounding liver • T1 C+ (Gd) • enhancement is usually arterial and may be brief – rapid wash out becoming hypointense compared to remainder of the liver (96% specific). This is on account of the supply to HCCs being from the hepatic artery rather than portal vein – rim enhancement may persist (referred to as a capsule) – the larger the lesion the more heterogeneous the enhancement • T2 - variable, typically hyperintense
  • 55. ARTERIAL PC WITH FAT SAT
  • 56. ARTERIAL PHASE MINUS PRE CONTRAST
  • 57. • A large HCC may have a number of characteristic features, such as a – mosaic pattern, – a tumor capsule, – extracapsular extension with formation of satellite nodules, – vascular invasion, and – extrahepatic dissemination, including lymph node and distant metastases
  • 58. Hepatic Metastases • Hepatic metastases can be classified according to their enhancement pattern into two categories: – hypovascular and hypervascular. • Hypovascular – Colon, lung, prostate, gastric, and transitional cell carcinomas • Hypervascular – Islet cell tumors, breast cancer, melanoma, thyroid cancer, and carcinoid tumor
  • 59. Hypovascular Metastases • These metastatic lesions usually demonstrate low signal intensity on T1-weighted MR images and are iso-to hyperintense on T2weighted images • Delayed enhancement on contrast-enhanced images. • Occasionally, they show early ring enhancement
  • 60. Early phase contrast-enhanced 3D GRE T1weighted VIBE MR image shows hypovascular metastases with low signal intensity and no enhancement (arrow).
  • 61. Hypervascular metastases are best seen during the arterial phase of enhancement .Most of these lesions have high signal intensity on T2-weighted MR images
  • 62. Lymphoma • Primary hepatic lymphoma is rare. • Secondary involvement of the liver can occur in up to 50% of patients with non-Hodgkin lymphoma and 20% of patients with Hodgkin lymphoma. • Lymphomatous lesions usually have low signal intensity on T1-weighted MR images and variable signal intensity on T2-weighted images. • They usually enhance minimally just after gadolinium administration and may show faint peripheral rim enhancement on subsequent images.
  • 63. Axial contrast-enhanced 3D GRE T1-weighted VIBE MR image demonstrates two small, well-defined hepatic lymphomatous deposits with faint marginal enhancement
  • 64. Recent advances • Recent advances in MRI have led to a growing interest in optimizing and applying functional MRI methods for assessment of liver disease. These methods include—but are not limited to— diffusion-weighted imaging (DWI), perfusion-weighted MRI, MR elastography (MRE), and MR spectroscopy (MRS).
  • 65. • DWI- Restricted diffusion observed in patients with cirrhosis - reflects diminished capillary perfusion • PWI-A prospective study of liver perfusion parameters showed increased arterial flow and distribution volume and decreased portal venous flow in patients with advanced fibrosis and cirrhosis • MRE-have tested the usefulness of the technique for diagnosing hepatic fibrosis. • MRS-for measuring hepatic fat content, – with many studies showing strong correlations between MRS and histologic grade of steatosis

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