Implementation of helical computed tomography in magnetic resonance imaging

PURPOSE: To provide a rapid sequence for volumetric imaging of large fields of view. MATERIALS AND METHODS: The volumetric imaging principles of x-ray helical computed tomograpy (CT) were implemented here on an MRI scanner. However, using the advantages offered by MRI, spiral trajectories in K-space were incorporated to make the helical scan more efficient. Thus, data acquisition and interpolations were conducted in K-space and images reconstructed by gridding and applying the inverse Fourier transform. The rapid spiral helical (RASH) imaging method was evaluated by computer simulations, by scanning phantoms and an in vitro heart, and by comparison to conventional multislice interleaved spirals (MSIS) imaging. RESULTS: A significant time saving (61.4% to 85.9%) relative to MSIS was achieved without significant degradation in image quality. Volume assessment and in-plane resolution by RASH were almost identical to the MSIS pulse sequence. The corresponding increase in effective slice width was estimated to range (for the values studied here) from 1.31 to 2.5 according to the selection of the helical pitch and the slice thickness used for imaging. CONCLUSION: The suggested method offers the advantages provided by x-ray helical CT and can be useful in MRI volumetric scanning of large objects.     

Rhabdomyolysis of the head and neck: computed tomography and magnetic resonance imaging findings

Rhabdomyolysis is rare in the head and neck. Early diagnosis and treatment is essential to prevent serious complications such as hyperkalaemia, acidosis, acute renal failure and disseminated intravascular coagulation. We present a case of rhabdomyolysis of the head and neck. CT and MRI findings supported the diagnosis of rhabdomyolysis with the patient's clinical and laboratory findings. While imaging is not crucial, it can aid in the detection of rhabdomyolysis and narrow the differential diagnosis along with laboratory findings and physical examination.     

Detection of local recurrent disease in musculoskeletal tumors: magnetic resonance imaging versus computed tomography

A 2 1/2-year prospective study of surgically treated malignant mesenchymal neoplasms showed magnetic resonance imaging (MRI) to be superior to computed tomography (CT) in sensitivity for local recurrent disease measuring less than 15 cm³. Larger masses were detected with similar sensitivity; specificity and predictive values did not differ. The presence of areas of high signal intensity on T2-weighted images proved to be a reliable criterion except in fibrous neoplasms. However, differentiation between non-hemorrhagic fluid collections, cross-sectioned veins or bowel contents and small tumor nodules cannot be made simply by signal intensity, but has to be based upon the evaluation of gross morphologic criteria.     

Preoperative evaluation of patients awaiting liver transplantation: comparison of multiphasic contrast-enhanced 3D magnetic resonance to helical computed tomography examinations

PURPOSE: To determine the feasibility of using a multiphasic magnetic resonance (MR) examination to evaluate the hepatic arterial anatomy and parenchyma in patients awaiting orthotopic liver transplantation (OLT). MATERIALS AND METHODS: Twenty consecutive patients awaiting OLT underwent multiphasic MR (using a T1-weighted 3D gadolinium-enhanced gradient-echo (GRE) sequence and two separate injections of contrast material) and computed tomography (CT) imaging; both imaging studies were performed within a 1-week period for each patient. Quantitative and qualitative assessment of the hepatic arterial system on MR data was performed. Two independent observers classified the hepatic arterial anatomy and evaluated the hepatic parenchyma from the MR data. The prospective CT interpretation was used as the gold standard. RESULTS: Overall qualitative rating of hepatic arterial system-to-background contrast on MR data was good to excellent (average pooled score of 2.00 +/- 0.27), with no significant difference between the two observers after the first or second injections of contrast material. Classification of hepatic arterial anatomy by MR angiography (MRA) and CT angiography (CTA) was concordant in 85% (17/20) of patients and discordant in 15% (3/20) of patients. Focal parenchymal lesions were detected in 25% (5/20) of patients by MR and CT; however, two lesions in one patient with multiple lesions were detected only with MR. CONCLUSION: Multiphasic T1-weighted 3D gadolinium-enhanced MR examination can provide comprehensive evaluation of the hepatic arterial anatomy and parenchyma in patients awaiting OLT. MR may offer an advantage over CT in the detection of focal parenchymal lesions.     

MRI与MRCP结合在胆管恶性梗阻性病变诊断中的应用价值

目的：探讨磁共振成像结合磁共振胰胆管成像技术对胆管恶性梗阻性病变的诊断价值。方法：收集30例经手术病理和临床治疗证实的胆管恶性梗阻性病例,回顾性分析其影像学表现。结果：30例患者MRI均表现为肝内外胆管不同程度阻塞性扩张。其中胆管癌23例,胆囊癌1例,肝细胞肝癌2例,转移瘤2例,壶腹癌2例。阻塞部位在肝内胆管部2例,肝门部10例,中部15例,壶腹部3例。所有病例均经临床或病理证实。结论：MRI与MRCP结合能显示胆管阻塞性扩张及阻塞部位,有较高的诊断价值。     

Low-grade fibromyxoid sarcoma of the small bowel mesentery: computed tomography and magnetic resonance imaging findings

Low-grade fibromyxoid sarcoma (LGFMS) is a rare tumor that commonly arises in the lower extremities but rarely in the mesentery. We report computed tomography (CT) and magnetic resonance imaging (MRI) findings of LGFMS of the small bowel mesentery. On CT, the mass was composed of two components. One component, on its right side, appeared to have isointense attenuation relative to muscle, whereas the other component, on its left side, appeared to have low attenuation. On MRI the mass on the right side showed hypointensity similar to muscle on both T1-and T2-weighted images as well as mostly slight enhancement on contrast-enhanced T1-weighted images. On the other hand, the mass on the left side showed relative hypointensity on T1-weighted images and hyperintensity on T2-weighted images as well as intense enhancement on contrast-enhanced T1-weighted images, suggesting that the tumor contained myxoid tissue. The myxoid area of LGFMS may have a tendency to reveal intense enhancement on contrast-enhanced images.     

Pancreatitis: computed tomography and magnetic resonance imaging

The value of CT in management of severe acute pancreatitis is well established. Some, but not all, experimental studies suggest a detrimental effect of intravenous iodinated contrast agents in acute pancreatitis, but although initial clinical data tends to support this, the positive advantages of enhanced CT outweigh the possible risks. Magnetic resonance imaging has been shown to be as effective as CT in demonstrating the presence and extent of pancreatic necrosis and fluid collections, and probably superior in indicating the suitability of such collections for percutaneous drainage. Image-guided intervention remains a key approach in the management of severely ill patients, and the indications, techniques and results of radiological intervention are reviewed herein. Both CT and MRI can be used to diagnose advanced chronic pancreatitis, with the recent addition of MRCP as a viable alternative to diagnostic endoscopic retrograde cholangiopancreatography (ERCP). Both MRCP and CT/MR imaging of the pancreatic parenchyma still have limitations in the recognition of the earliest changes of chronic pancreatitis – for which ERCP and tests of pancreatic function remain more sensitive – but the clinical significance of these minor changes remains contentious. Received: 12 February 1998; Revision received: 17 June 1998; Accepted: 22 June 1998     

Small bowel obstruction: the role of computed tomography in its diagnosis and management with reference to other imaging modalities

Small bowel obstruction is a leading cause of acute surgical admissions for abdominal pain. There is an increasing tendency for initial conservative management rather than immediate operative intervention, as a proportion of cases will resolve spontaneously. This has resulted in a growing reliance on radiological investigations to reassure the surgeon that medical therapy can be safely instituted. The onus therefore rests with radiologists to guide their surgical colleagues by correctly interpreting the plain abdominal radiograph and suggesting appropriate further investigation if warranted. Recently, computed tomography (CT) has been proposed as the test of choice to define the level and cause of acute small bowel obstruction and to identify complications such as ischaemia and perforation which will prompt surgical intervention. This review will discuss the utility of early CT in the diagnosis of acute small bowel obstruction and outline its impact on patient management.     

Imaging diabetes mellitus with coronary computed tomography angiography, cardiovascular magnetic resonance, and positron emission tomography

The prevalence and medical expense associated with diabetes mellitus continue to increase. Using the diagnostic imaging techniques of coronary computed tomography angiography, cardiovascular magnetic resonance, and positron emission tomography, it may be possible to make earlier, non-invasive diagnoses of the type and extent of disease, thereby preventing or delaying some morbidity and mortality.     

Dumbbell-shaped thoracic hibernoma: computed tomography and magnetic resonance imaging findings

Hibernoma is an uncommon, benign soft tissue tumor that arises in brown adipose tissue. The computed tomography (CT) and magnetic resonance imaging (MRI) findings of hibernomas are similar to those of well-differentiated liposarcoma or angiolipoma. We report the unique appearance of a rare thoracic wall hibernoma, which appeared as a dumbbell-shaped lipomatous tumor across an intercostal region. A dynamic contrast-enhanced study on MRI revealed early enhancement, which corresponded to the branching low-signal intensity on T2-weighted images of the mass.     

Central nervous system aspergillosis: magnetic resonance imaging, diffusion-weighted imaging, and magnetic resonance spectroscopy features

Aspergillus infection is invasive in nature in the immunosuppressed population and disseminates throughout the body, with the brain being a common site. Conventional magnetic resonance imaging (MRI) combined with diffusion-weighted imaging (DWI) and magnetic resonance spectroscopy (MRS) play a life-saving role in the early diagnosis and treatment monitoring of this potentially fatal infection. We present MRI, DWI, and MRS findings of a case of central nervous system aspergillosis with treatment follow-up.     

Primary heart angiosarcoma detected by computed tomography and magnetic resonance imaging

We report a case of primary heart angiosarcoma and its appearance on plain and post-contrast computed tomography and magnetic resonance imaging in 21-year-old woman. The tumour involved the right atrium, expanded superiorly among the superior vena cava, ascending aorta and innominate vein, and infiltrated the pericardium. The tumour was disseminated into lungs, liver and bones at the time of its clinical presentation. Received 24 January 1997; Revision received 13 March 1997; Accepted 28 April 1997     

Non-cardiac findings on coronary computed tomography and magnetic resonance imaging

Both multislice computed tomography (CT) and magnetic resonance imaging (MRI) are emerging as methods to detect coronary artery stenoses and assess cardiac function and morphology. Non-cardiac structures are also amenable to assessment by these non-invasive tests. We investigated the rate of significant and insignificant non-cardiac findings using CT and MRI. A total of 108 consecutive patients suspected of having coronary artery disease and without contraindications to CT and MRI were included in this study. Significant non-cardiac findings were defined as findings that required additional clinical or radiological follow-up. CT and MR images were read independently in a blinded fashion. CT yielded five significant non-cardiac findings in five patients (5%). These included a pulmonary embolism, large pleural effusions, sarcoid, a large hiatal hernia, and a pulmonary nodule (>1.0 cm). Two of these significant non-cardiac findings were also seen on MRI (pleural effusions and sarcoid, 2%). Insignificant non-cardiac findings were more frequent than significant findings on both CT (n = 11, 10%) and MRI (n = 7, 6%). Incidental non-cardiac findings on CT and MRI of the coronary arteries are common, which is why images should be analyzed by radiologists to ensure that important findings are not missed and unnecessary follow-up examinations are avoided.     

Ultrasonography, computed tomography and magnetic resonance imaging for diagnosis of ovarian carcinoma

Our objective was to compare US, CT, and MR imaging in differentiation of malignant from benign ovarian tumors. Through an electronic literature search and manual review of bibliographies (January 1990 to June 2006), relevant studies on the diagnostic performance of US, CT, and MR imaging in the differentiation between benign and malignant ovarian tumours were identified. Sixty-nine articles were included, yielding 143 studies. Data on the accuracy of the different imaging modalities were analyzed and compared by constructing summary receiver-operating characteristic (ROC) curves. Our results suggest that US techniques seems to be similar with CT and MRI in differentiation of malignant from benign ovarian tumors. The results also revealed that color Doppler flow imaging alone is significantly inferior to combined US techniques, morphologic assessment alone and contrast enhanced US in diagnosis of ovarian cancer. In conclusion, US morphologic assessment still is the most important and common modality in detect ovarian cancer.     

Ultrasound and magnetic resonance imaging assessmentof active bowel segments in Crohn's disease

AIM: Determining bowel disease activity in Crohn's patients can be difficult on clinical and laboratory assessment. Endoscopy is invasive and barium studies use ionising radiation. The aim of this study was to compare ultrasound and magnetic resonance imaging (MRI) in detecting Crohn's disease activity in the small or large bowel. MATERIALS AND METHODS: Thirty patients, previously diagnosed with Crohn's disease, had bowel ultrasound and MR imaging, and were deemed active or inactive on each test. The 'gold standard' was based on clinical assessment and one or more of the following: endoscopy, barium studies or surgery. RESULTS: For determining Crohn's disease activity, the sensitivities and specificities of bowel ultrasound and MRI were 87 percent and 100 percent, and 87 percent and 71 percent, respectively. Significant parameters that defined disease activity were bowel wall thickening on ultrasound and MRI, and contrast enhancement of the bowel wall and mesenteric vascularity/stranding on MRI. CONCLUSION: Ultrasound and MRI were both sensitive for determining Crohn's disease activity in the bowel, but MRI with gadolinium enhancement was less specific.     

Ameloblastic carcinoma of the mandible with metastasis to the skull and lung: advanced imaging appearance including computed tomography,magnetic resonance imaging and positron emission tomography computed tomography

Ameloblastic carcinoma is a very rare malignant odontogenic tumour with characteristic histopathological and clinical features, which requires aggressive surgical treatment and surveillance and, therefore, differs from ameloblastoma. Metastasis typically occurs in the lung. Only one patient with metastasis to the skull has previously been described and no prior case reports have presented MRI and positron emission tomography-CT (PET-CT) imaging findings. We describe a case of ameloblastic carcinoma with metastasis to the skull and lung with emphasis on imaging features including MRI and PET-CT.     

Sturge-Weber syndrome: diffusion magnetic resonance imaging and proton magnetic resonance spectroscopy findings

We report on the diffusion magnetic resonance imaging (MRI) and proton MR spectroscopy findings of a 26-year-old female patient with Sturge-Weber syndrome. Echo-planar trace diffusion MRI revealed mildly high signal intensity changes at parieto-occipital lobes on b = 1000 s/mm² images, suggesting restricted diffusion. On corresponding apparent diffusion coefficient maps, those areas had moderately high signal intensity and high apparent diffusion coefficient values (around 0.9×10(-3) mm²/s) compared with the contralateral symmetrical normal side of the brain (0.776×10(-3) mm²/s). This finding was consistent with increased motion of water molecules (disintegration of the neural tissue) in these regions. Proton MR spectroscopy revealed decreased N-acetyl aspartate and increased choline peaks, indicating disintegration of neural tissue associated with neuronal loss as well.     

Computed tomography and magnetic resonance imaging evaluation of patellofemoral instability

Malalignment and tracking abnormalities of the patellofemoral joint are common causes of anterior knee pain,which are often difficult to evaluate clinically. Conventional radiography, as well as the cross-sectional imaging modalities of computed tomography (CT) and magnetic resonance imaging (MRI) are useful tools for both detecting and quantifying these abnormalities. Acute transient dislocation of the patella, on the other hand, is a relatively uncommon injury accounting for only 2% to 3% of all acute injuries of the knee, and can also be a difficult diagnosis to establish on the basis of history and physical findings alone. MRI is a sensitive, noninvasive method for detecting prior acute transient dislocation of the patella. This article begins by describing the role of CT and MRI as it pertains to the detection of abnormal patellofemoral tracking. Both static and dynamic techniques are described along with the standard criteria used to establish and quantify patellofemoral malalignment abnormalities. Next, the constellation of MRI findings most commonly encountered after acute transient dislocation of the patella are described. These findings include a typical bone bruise pattern involving the anterolateral aspect of the lateral femoral condyle and inferomedial patella, hemarthrosis, and injury to the medial soft-tissue restraints (especially the medial patellofemoral ligament). After transient dislocation of the patella, patients with significant osteochondral injury or disruption of the medial soft-tissue restraints may benefit from surgical repair. The role of MRI in preoperative planning is discussed as it relates to the detection of osteochondral injuries as well as injury to the medial soft-tissue restraints.     

Magnetic resonance imaging in determination of myocardial ischemia and viability: comparison with positron emission tomography and single-photon emission computed tomography in a porcine model

Background: In patients with chronic left ventricular dysfunction, the size of the viable cardiac muscle is correlated with the prognosis and the outcome of myocardial revascularization.

Purpose: To evaluate the diagnostic value of various imaging techniques in determination of myocardial ischemia and viability.

Material and Methods: A chronic myocardial ischemia animal model was established, in which 10 pigs underwent magnetic resonance imaging (MRI), positron emission tomography (PET), and single-photon emission computed tomography (²⁰¹Tl SPECT) before and 1-2 months after modeling. The size of myocardial ischemia and necrosis was judged, and the imaging manifestations were compared with pathologic findings.

Results: Seven of the 10 animals completed all examinations uneventfully. On dobutamine-stressed cine MRI, 10 (8.93%) segments were found to be akinetic. Perfusion was abnormal in 34 (30.35%) segments. Delayed hyperenhancement was observed in 12 (10.71%) segments. PET detected myocardial necrosis in 17 (15.18%) segments, and SPECT detected myocardial necrosis in nine (8.04%) segments. Histological examination with triphenyltetrazolium chloride (TTC) showed pale necrosis in 14 (12.50%) segments. The number of necrotic segments detected by PET was significantly greater than that by contrast-enhanced MRI (χ² = 5, P = 0.0253, kappa = 0.8028) and cine MRI (χ² = 7, P = 0.0082, kappa = 0.7079). It was also greater than that by TTC (χ² = 3, P = 0.0833, kappa = 0.8879), although the difference was statistically insignificant. The number of necrotic segments detected by SPECT was significantly smaller than that by TTC (χ² = 5, P = 0.0253, kappa = 0.7590), as was the number of necrotic segments detected by cine MRI (χ² = 4, P = 0.0455, kappa = 0.8100). There was no statistically significant difference in the detection of necrotic segments between contrast-enhanced MRI and TTC (χ² = 2, P = 0.1573, kappa = 0.9130).

Conclusion: Cardiac MRI can determine viable myocardium and clearly delineate the location and degree of myocardial necrosis. PET slightly overestimates the extent of the necrotic myocardium and is unable to distinguish transmural necrosis from subendocardial necrosis.     

Low b-value diffusion-weighted imaging for diagnosing strangulated small bowel obstruction: a feasibility study

Purpose:

To assess the feasibility of low b‐value diffusion‐weighted imaging (DWI) for diagnosing strangulated small bowel obstruction (SBO).

Materials and Methods:

Five volunteers and 14 patients with SBO underwent DWI at b‐values of 0 and 50 s/mm². Apparent diffusion coefficients (ADCs) and signal preservation ratios (SPRs) were measured in the distal jejunum in the volunteers before and after butylscopolamine administration, and in the (strangulated) closed loop, near the obstructive site, and far from the obstructive site in the patients. Low b‐value diffusion‐weighted images in the patients were quantitatively evaluated for diagnosing strangulation.

Results:

In the volunteers, mean ADC (10^?3 mm²/s) and SPR (%) before butylscopolamine administration (18.3 ± 5.9 and 41.4 ± 11.5) were significantly different (P < 0.05) from those after butylscopolamine administration (6.4 ± 3.6 and 73.7 ± 12.9). In the patients, mean ADCs and SPRs among the strangulated closed loop (3.8 ± 2.2 and 83.3 ± 9.3), near the obstructive site (12.1 ± 6.9 and 57.3 ± 18.5), and far from the obstructive site (26.8 ± 10.7 and 29.9 ± 16.4) were significantly different (P < 0.05). Areas under the receiver operating characteristic curve for the diagnosis of strangulation varied between 0.937 and 1.000.

Conclusion:

Low b‐value DWI is a feasible technique to distinguish the strangulated closed loop from nonstrangulated loops in SBO, and show promise for diagnosing strangulated SBO. J. Magn. Reson. Imaging 2011;. © 2011 Wiley Periodicals, Inc.