MRI

Voxel-wise correlation of PET/CT with multiparametric MRI and histology of the prostate using a sophisticated registration framework.

OBJECTIVES:

To develop a registration framework for correlating positron emission tomography/computed tomography (PET/CT) images with multiparametric MRI (mpMRI) and histology of the prostate, thereby enabling voxel-wise analysis of imaging parameters.

PATIENTS AND METHODS:

In this prospective proof-of-concept study, nine patients scheduled for radical prostatectomy underwent mpMRI and PET/CT imaging prior to surgery. One had PET imaging using 18 F-fluoromethylcholine (FCH), five using 68 Ga-labelled prostate-specific membrane antigen (PSMA)-HBED-CC (PMSA-11) and three using a trial 68 Ga-labelled THP-PSMA tracer. PET/CT data was co-registered with mpMRI via the CT scan and an in vivo 3D T2w MRI, and then co-registered with ground truth histology data using ex vivo MRI of the prostate specimen. Maximum and mean standardised uptake values (SUVmax and SUVmean) were extracted from PET data using tumour annotations from histology, and Kolmogorov-Smirnov tests were carried out to compare between tumour and benign voxel values. Correlation analysis was performed between mpMRI and PET SUV tumour voxels using Pearson’s correlation coefficient and R squared statistics.

RESULTS:

PET/CT data from all nine patients were successfully registered with mpMRI and histology data. SUVmax and SUVmean ranged from 2.21 to 12.11 and 1.08 to 4.21, respectively. All patients showed the PET SUV values in benign and tumour voxels were from statistically different distributions. Correlation analysis showed no consistent trend between the T2w or ADC values and PET SUV. However, parameters from DCE MRI including the maximum enhancement (ME), volume transfer constant Ktrans and the initial area under the contrast agent concentration curve (iAUGC60) showed consistent positive correlations with PET SUV. Furthermore, R2* values from BOLD MRI showed consistent negative correlations with PET SUV voxel values.

CONCLUSION:

We have developed a novel framework for registering and correlating PET/CT data at a voxel-level with mpMRI and histology. Despite registration uncertainties, perfusion and oxygenation parameters from DCE MRI and BOLD imaging showed correlations with PET SUV. Further analysis will be performed on a larger patient cohort to quantify these proof-of-concept findings. Improved understanding of the correlation between mpMRI and PET will provide supportive information for focal therapy planning of the prostate.

MRI findings of posttraumatic intrahepatic vascular shunts.

Purpose

To describe the features of posttraumatic intrahepatic vascular shunts (PIVS) as seen on MRI.

Materials and Methods

A search was performed for patients with MRI features compatible with PIVS in the Abdominal MRI databases between January 2002 and March 2008. This study was approved by our institutional review board. All patients were imaged using a protocol that included noncontrast T1‐weighted and T2‐weighted images, and postgadolinium gradient‐echo images.

Results

Eleven patients (eight men, three women; mean age 55.36 years; range 43–77 years) were identified with PIVS. The following imaging features were observed: dilation of afferent and efferent vessels (five patients), transient hepatic parenchymal blush in a watershed distribution (11 patients), and early opacification of efferent vessels (11 patients).

Conclusion

Patients with PIVS exhibit features that are distinctive for this entity and include: dilatation of efferent and afferent vessels, transient parenchymal blush, and early opacification of efferent vessels.

MR Imaging: Sequences we use and why.

Typically there are at least 8 different sets of images in a body magnetic resonance imaging (MRI) study, which can bewilder the radiologist who may be comfortable with looking at only 1 set of images required by computed tomography (CT). The standard MR sequences obtained are: noncontrast T1-weighted (T1W) in-phase, out-of-phase and fat-suppressed images, and T2-weighted (T2W) fat- and non-fat-suppressed images. Other standard sequences include contrast-enhanced T1W sequences imaged during the hepatic arterial dominant phase, early hepatic venous phase and the interstitial phase (Figure 1). This review describes the core data interpretation from these different imaging sets to raise the comfort level for image interpretation of abdominal MRI studies.

MR imaging findings of small bowel hemorrhage: two cases of mural involvement and one of perimural.

Purpose

To demonstrate the MR appearance of small bowel wall hemorrhage.

Materials and Methods

A search was performed of the clinical information system (CIS) and the abdominal MRI databases of our institution for patients diagnosed with bowel hemorrhage on MRI between January 1, 2000, and July 31, 2008. All patients were imaged using a protocol that included noncontrast T1‐ and T2‐weighted images and postgadolinium gradient echo images.

Results

Two male patients, 44 and 55 years of age, were identified with small bowel mural hemorrhage, one in the duodenum and one in the jejunum. A third patient, a 66‐year‐old man, was identified with perimural hematoma. The following imaging features were observed: for mural hemorrhage, mural‐based increased signal intensity (SI) in the bowel wall on fat suppressed T1‐weighted images, variable increased SI on T2‐weighted images and no appreciable enhancement on the postcontrast T1‐weighted image; perimural hemorrhage exhibited normal thickness low SI wall on T2‐weighted single shot images, with ill‐defined material surrounding the bowel. SI features of this material, was similar to mural‐based abnormality.

Conclusion

In two patients with small bowel wall hemorrhage, the wall showed increased thickness with increased SI on noncontrast T1‐weighted images and lack of enhancement on postgadolinium images. Perimural hematoma showed an intact normal thickness wall that was low SI on T2 with surrounding material that was high SI on noncontrast T1‐weighted images and did not enhance.

Magnetic Resonance Imaging of Gallbladder and Biliary System

Gallbladder and biliary system pathologic component is a spectrum of benign and malignant conditions. Standard magnetic resonance imaging techniques when used together with magnetic resonance cholangiopancreatography (MRCP) can evaluate gallbladder and biliary system pathologic conditions. Inflammatory diseases are characterized by thickening and intense mucosal contrast enhancement of the affected bile ducts and or gallbladder wall. Postinflammatory changes can be appreciated on MRCP with short or long segment strictures of the bile ducts. Serial contrast-enhanced images show reactive inflammatory changes in the liver parenchyma. Neoplastic diseases of the gallbladder and the biliary tree are evaluated on T2-weighted fat-suppressed echo train and serial contrast-enhanced images and their obstructive effect can be displayed on MRCP images. In this paper, we will review the spectrum of MRI findings of gallbladder and biliary system pathologic conditions.

Debris-filled Biliary System – A difficult Diagnosis on MRI and MRCP.

We describe a debris-filled biliary system as a difficult diagnosis using magnetic resonance imaging and magnetic resonance cholangiopancreatography (MRCP). A male patient aged 60 years showed a nonvisualized biliary system due to complete filling with debris. The following imaging features were observed: mild heterogeneity of intermediate signal on T2-weighted, MRCP and T1-weighted images and mild heterogeneous enhancement of periportal tissue on early and late postcontrast images. The absence of simple-appearing bile on T2 or MRCP images made the diagnosis of dilated, debris-filled biliary system challenging.

Diagnostic yield of FDG PET/CT, MRI, and CSF cytology in nonbiopsiable Neurolymphomatosis as a heralding feature of Diffuse B-cell Lymphoma recurrence.

Neurolymphomatosis (NL) is a rare condition associated with lymphomas in which various structures of the nervous system are infiltrated by malignant lymphocytes. Rarely, it may be the presenting feature of recurrence of lymphoma otherwise deemed to be in remission. It is crucial, as is the case with all types of nodal or visceral involvement of lymphoma, to identify the disease early and initiate treatment with chemotherapy and/or radiation therapy. Positron emission tomography-computed tomography (PET-CT) has been shown to be a sensitive modality for staging, restaging, biopsy guidance, therapy response assessment, and surveillance for recurrence of lymphoma. Magnetic resonance imaging (MRI) is another useful imaging modality, which, along with PET/CT, compliment cerebrospinal spinal fluid (CSF) cytology and electromyography (EMG) in the diagnosis of NL. Performing nerve biopsies to confirm neurolymphomatosis can be challenging and with associated morbidity. The case presented herein illustrates the practical usefulness of these tests in detecting NL as a heralding feature of lymphoma recurrence, especially in the absence of histopathologic correlation.

Quantitative Imaging Analysis of FDG PET/CT Imaging for Detection of Central Neurolymphomatosis in a Case of Recurrent Diffuse B-Cell Lymphoma

Neurolymphomatosis (NL) is a rare disease characterized by malignant lymphocytes infiltrating various structures of the nervous system. It typically manifests as a neuropathy involving the peripheral nerves, nerve roots, plexuses, or cranial nerves. It often presents as a complication of lymphoma, but it can be the presenting feature of recurrent lymphoma. It is essential to identify and initiate treatment early with chemotherapy and/or radiation therapy in all cases of nodal or visceral (including neural) involvement with lymphoma. There are various diagnostic tests that can be used for its detection, such as cerebrospinal spinal fluid (CSF) cytology, electromyography (EMG), magnetic resonance imaging (MRI), and positron-emission tomography/computed tomography (PET/CT). FDG-PET/CT is the standard of care in lymphoma staging, restaging, and therapy response assessment, but has an inherent limitation in the detection of disease involvement in the central nervous system. While that is mostly true for visual assessment, there are quantitative methods to measure variation in the metabolic activity in the brain, which in turn helps detect the occurrence of neurolymphomatosis.