MR imaging of the heart: functional imaging

To date, most applications of cardiovascular MRI relate to the evaluation of major vessels rather than the heart itself. However, MRI plays a major role in the evaluation of specific types of cardiovascular pathology, namely intracardiac and paracardiac masses, pericardial disease, and congenital heart disease. In addition, because the visualization of cardiovascular anatomy with MR is non-invasive and permits three-dimensional analysis but also allows functional assessment of the cardiac pump, it is clear that MRI will have a growing and significant impact over the next years. We review some of the technical aspect of cardiac MRI and describe the current and potential clinical and investigative applications of this new methodology.     

Intracranial dural arteriovenous fistula with spinal medullary venous drainage

We report on a 46-year-old patient in whom an intracranial dural arteriovenous (AV) fistula, supplied by a branch of the ascending pharyngeal artery, drained into spinal veins and produced rapidly progressive symptoms of myelopathy and brainstem dysfunction including respiratory insufficiency. Magnetic resonance imaging studies demonstrated brainstem oedema and dilated veins of the brainstem and spinal cord. Endovascular embolization of the fistula led to good neurological recovery, although the patient had been paraplegic for 24 h prior to embolization. This case demonstrates the MRI characteristics of an intracranial dural AV fistula with spinal drainage and illustrates the importance of early diagnosis and treatment. Even paraplegia may be reversible, if angiography is performed and the fistula treated before ischaemic and gliotic changes become irreversible. Received: 25 May 1999; Revised: 25 January 2000; Accepted: 15 February 2000     

van der Knaap syndrome: MR imaging findings including FLAIR, diffusion imaging, and proton MR spectroscopy

A patient is reported with diffuse leukoencephalopathy associated with cystic degeneration of the white matter of the brain (van der Knaap syndrome). The changes were studied by fluid attenuated inversion recovery (FLAIR), and diffusion-weighted MR imaging. The FLAIR sequence revealed suppressed signal of the cysts, and widespread high-signal white matter changes associated with thinned cortices. On diffusion-weighted MR imaging, apparent diffusion coefficient (ADC) values ranged from 3.0 × 10^–3 to 2.7 × 10^–3 mm²/s in the temporal cysts, similar to that of CSF. The ADC values within the parenchyma ranged between 2 × 10^–3 and 2.1 × 10^–3 mm²/s, a value falling between normal parenchyma and cerebrospinal fluid, compared with a control group of three healthy subjects. The changes were also evaluated by proton MR spectroscopy, and were compared with a control group of 12 cases. Magnetic resonance spectroscopy revealed apparently increased NAA/Cr ratios in most parts of the brain. The NAA/Cho ratios were either high or low, and the Cho/Cr ratios were increased or normal in different regions. Received: 27 October 1999; Revised: 9 December 1999; Accepted: 20 December 1999     

Depiction of anomalous coronary vessels and their relation to the great arteries by magnetic resonance angiography

Three-dimensional respiratory-gated coronary MR angiography (MRA) allowed accurate analysis of the anatomy of the coronary arteries and their relation to the adjacent anatomic structures in two patients with anomalous origin and proximal course of the coronary vessels. Together with functional tests, it decisively influenced further therapy. Received: 16 November 1999; Revised: 4 April 2000; Accepted: 3 May 2000     

Follow-up of patients with previous treatment for coarctation of the thoracic aorta: comparison between contrast-enhanced MR angiography and fast spin-echo MR imaging

Regular follow-up is required in patients with previous intervention for coarctation of the aorta to detect recoarctation or aneurysm formation. In this study we describe the findings encountered on routine follow-up exams and we compare the use of contrast-enhanced 3D MR angiography (CE MRA) with fast spin-echo MRI (FSE) to study the thoracic aorta after previous intervention. In 51 consecutive patients previously treated for aortic coarctation, 74 MR studies of the thoracic aorta were performed during a 2-year period using CE MRA and FSE MRI. The thoracic aorta was evaluated for abnormalities of course, caliber, shape, and pathology of side branches. The CE MRA and FSE MRI studies were evaluated side by side by consensus of two reviewers evaluating which MR technique depicted the abnormalities of the thoracic aorta the best. Of 74 exams, six clinically important abnormalities were found: four aneurysms and two restenoses. Two small pseudoaneurysms were missed on the FSE studies. Contrast-enhanced MRA was judged to visualize aortic abnormalities better than FSE (47 of 74 MR studies) especially for the transverse aortic arch, coarctation site, left subclavian artery, and aortic arch configuration. For the ascending aorta and distal descending aorta, CE MRA and FSE performed equally well. Aortic diameters measured at four levels in the first 18 MRI studies showed no significant differences in diameter when measured by FSE or CE MRA (p = not significant). Clinically important abnormalities, such as aneurysm formation and restenosis, can be present years after treatment for aortic coarctation. In the regular follow-up of these patients, CE MRA may provide additional diagnostic information compared with FSE and should be included as part of the routine exam. Received: 3 April 2000; Revised: 5 July 2000; Accepted: 7 July 2000     

Angiomyolipoma of the liver: ferumoxides-enhanced MR imaging

We report a case of angiomyolipoma of the liver with emphasis on the appearance at MRI after administration of ferumoxides. Post-contrast T1- and T2-weighted images showed a frank decrease of signal intensity in a rim on the margin of the tumor. This unusual finding was related to the presence of an increased number of CD68-positive histiocytic cells in the periphery of the lesion and in the adjacent liver parenchyma. Received: 13 September 1999; Revised: 2 February 2000; Accepted: 3 February 2000     

Prognostic value of perfusion- and diffusion-weighted MR imaging in first 3 days of stroke

The aim of this study was to evaluate the differences in cerebral perfusion seen on mean transit time (MTT) and cerebral blood volume (CBV) maps and to assess the subsequent prognostic value of the MTT–DWI (diffusion-weighted MRI) and CBV–DWI mismatch in the first three days of stroke on lesion enlargement and clinical outcome. In 38 patients, imaged 1–46 h after onset of symptoms, lesion volumes on proton-density (PD)-weighted MRI, DWI and PWI (both MTT and CBV maps) were compared with lesion volumes on follow-up PD-weighted scans, and to clinical outcome (National Institutes of Health Stroke Scale, Barthel index, and Rankin scale). The MTT-CBV, MTT–DWI and CBV–DWI mismatches were compared with change in lesion volume between initial and follow-up PD-weighted scans. Lesion volume on both DWI and PWI correlated significantly with clinical outcome parameters (p < 0.001) with strongest correlation for lesion volume on CBV. Perfusion–diffusion mismatches were found for both CBV and MTT and correlated significantly with lesion enlargement on PD-weighted imaging with strongest correlation for the CBV–DWI mismatch. The CBV–DWI mismatch has the highest accuracy in predicting lesion size on follow-up imaging and in predicting clinical outcome. Lesion volume measurements on CBV maps have a higher specificity than on PD-weighted, MTT or DWI images in predicting clinical follow-up imaging and in predicting clinical outcome. Received: 21 January 2000; Revised: 18 April 2000; Accepted: 20 April 2000     

The role of MR imaging in invasive cervical carcinoma

In this article the role of MR imaging in the management of cervical cancer is reviewed and illustrated. The appearance of the normal uterine cervix and of cervical carcinoma is shown. Important factors for optimal MR imaging of cervical carcinoma are reviewed. The value of MR imaging in the staging of cervical carcinoma is illustrated by showing parametrial invasion and lymph node involvement. Finally, the value of MR imaging staging is compared with clinical staging, CT staging, and surgical findings. The role of new imaging techniques, such as fast dynamic enhanced MR imaging, is described. Received: 12 April 1999; Revised: 13 July 1999; Accepted: 14 July 1999     

MR imaging of lumbar facet joint synovial cysts

The increasing application of magnetic resonance (MR) imaging of the spine has raised the awareness of lumbar facet synovial cysts (LFSC). This well recognised, yet uncommon condition, presents with low back pain and radiculopathy due to the presence of an extradural mass. The commonest affected level is L4/5 with a mild degenerative spondylolisthesis a frequent associated finding. MR imaging is the technique of choice to detect and diagnose a LFSC. This pictorial essay, drawing on experience of 43 cases seen in 40 patients, illustrates the spectrum of appearances that can be encountered and suggest differing causes for the variable signal characteristics exhibited. Computed tomography (CT) can be of value in some cases to aid interpretation of the MR images. In addition, CT facet arthrography by injection of air or iodinated non-ionic contrast medium may be used to confirm the diagnosis in doubtful cases as well as noting whether the patients presenting symptoms can be provoked. A comprehensive review of the existing literature is presented. Received: 22 September 1998; Revised: 29 June 1999; Accepted: 30 June 1999     

Craniocervical artery dissection: MR imaging and MR angiographic findings

Dissection of the carotid and vertebral arteries is a not so uncommon cause of stroke and has to be considered as a differential diagnosis especially in younger patients. Therapeutic and prognostic implications are different from those in extracranial atherosclerotic disease. Dissection results from hemorrhage into the vessel wall usually between the layers of the media. Digital subtraction angiography (DSA) depicts the resulting luminal compromise that may reveal some typical, but not specific, findings. The same is true for non-invasive angiographic techniques such as time-of-flight magnetic resonance angiography (MRA) and computed tomography angiography (CTA), which have shown accurate results compared with DSA. The main advantage of these techniques is the direct visualization of the vessel wall confirming the intramural hematoma. This is achieved best with MR imaging due to the high signal of blood degradation products on T1- and T2-weighted images. Therefore, MRI in combination with MRA is presently the method of choice for initial diagnosis and follow-up of craniocervical artery dissection (CCAD). In some questionable cases, CTA is a non-invasive alternative that is independent of flow phenomena. Received: 4 May 1998; Revision received: 8 September 1998; Accepted: 10 November 1998     

T1-relaxation kinetics of extracellular, intracellular and intravascular MR contrast agents in normal and acutely reperfused infarcted myocardium using echo-planar MR imaging

The objective of this study was to determine and compare if MR contrast agents distributed into various compartments can provide estimation of fractional distribution volume (FDV) in normal and infarcted myocardium using inversion recovery echo-planar MR imaging (IR EPI). Three different types of MR agents were investigated: (a) an extracellular agent, GdDTPA-BMA (0.1 mmol/kg); (b) an intravascular agent, GdDTPA-albumin (0.025 mmol/kg); and (c) an intracellular agent, manganese chloride (0.025 mmol/kg). The null point was determined from a series of IR EPI images in which TI was varied. Temporal changes in ΔR1 (ΔR1 = 1/T1_post-1/T1_pre) were measured during the initial 29–59 min after administration. Rats (n = 24) were subjected to 1-h coronary artery occlusion/reperfusion. Histochemical staining confirmed the presence and location of infarction. GdDTPA-BMA caused increase in ΔR1 of infarction < blood < < normal myocardium. ΔR1 ratios were 1.55 ± 0.08 for infarction and 0.33 ± 0.03 for normal myocardium, consistent with FDV of 0.82 ± 0.04 and 0.18 ± 0.01. The fractional distribution of this agent in normal myocardium approximated the extracellular space of myocardium. GdDTPA-albumin caused increase in ΔR1 of blood < < infarction < < normal myocardium. ΔR1 ratio in normal, but not infarcted, myocardium was constant at 0.10 ± 0.02 and approximated fractional blood volume. MnCl₂ caused equivalent increase in ΔR1 of normal and infarcted myocardium. ΔR1 of normal myocardium did not change overtime, whereas ΔR1 of blood rapidly decreased, leading to overestimation of FDV in normal and infarcted myocardium. In conclusion, extracellular, intravascular and intracellular MR contrast agents exhibited different T1-relaxation kinetics in both normal and infarcted myocardium. Constant ΔR1 ratio (myocardium/blood) after administration of MR contrast agent is a prerequisite for estimation of FDV of MR contrast agent in myocardium. Received: 22 December 1998; Revised: 7 April 1999; Accepted: 18 May 1999     

Dedicated extremity MR imaging of the foot and ankle

The purpose of this review is to provide illustrative examples of diseases of the foot and ankle when imaged with a low-field MR imaging system. A retrospective review of 268 foot and ankle examinations, performed in our institution within the past 3 years with a 0.2-T (Artoscan Esaote, Genoa, Italy) dedicated extremity MR system was done. Additionally, illustrative comparison with conventional radiography and high-field MR imaging is presented in patients in whom these examinations were also performed. Although motion artifact limited the value of a few studies, in the majority of examinations low-field MR imaging provided diagnostic image quality for the full spectrum of disorders affecting the foot and ankle and seemed to be a feasible alternative to high-field MR imaging in establishing an accurate diagnosis. Received: 23 November 1998; Revision received: 8 February 1999; Accepted: 4 June 1999     

Pulmonary arteriovenous malformation: Characterization with time-resolved ultrafast 3D MR angiography

To avoid potentially deadly consequences from paradoxical emboli, early detection and accurate characterization of pulmonary arteriovenous malformations (AVMs) is highly desirable. We report on a patient with a suspected pulmonary AVM who underwent ultrafast time-resolved 3D MR angiography of the pulmonary arteries. The case documents the suitability of the MRA technique as a noninvasive alternative to computed tomographic angiography and digital subtraction angiography for accurate pre-therapeutic characterization of pulmonary AVMs.     

MR imaging and MR angiography in popliteal artery entrapment syndrome

Popliteal artery entrapment (PAE) syndrome is an uncommon congenital anomaly seen in young adults causing ischemic symptoms in the lower extremities. It is the result of various types of anomalous relationships between the popliteal artery and the neighboring muscular structures. The purpose of this study was to define the role of MR imaging combined with MR angiography in the diagnosis of PAE cases. Four cases with segmental occlusion and medial displacement of popliteal artery in digital subtraction angiography (DSA) examinations were diagnosed as PAE syndrome by MR imaging and MR angiography. The DSA and MRA images are compared. All of the cases showed various degrees of abnormal intercondylar insertion of the medial head of the gastrocnemius muscle. The MR images showed detailed anatomy of the region revealing the cause of the arterial entrapment. Subclassification of the cases were done and fat tissue filling the normal localization of the muscle was evaluated. The DSA and MRA images demonstrated the length and localization of the occluded segment and collateral vascular developments equally. It is concluded that angiographic evaluation alone in PAE syndrome might result in overlooking the underlying cause of the arterial occlusion, which in turn leads to unsuccessful therapy procedures such as balloon angioplasty. Magnetic resonance imaging combined with MR angiography demonstrates both the vascular anatomy and the variations in the muscular structures in the popliteal fossa successfully, and this combination seems to be the most effective way of evaluating young adults with ischemic symptoms suggesting PAE syndrome. Received 7 April 1997; Revision received 15 July 1997; Accepted 13 November 1997     

Two-dimensional thick-slice MR digital subtraction angiography for assessment of cerebrovascular occlusive diseases

Although spatial resolution of current MR angiography is excellent, temporal resolution has remained unsatisfactory. We evaluated clinical applicability of 2D thick-slice, contrast-enhanced subtraction MR angiography (2D-MR digital subtraction angiography) with sub-second temporal resolution in cerebrovascular occlusive diseases. Twenty-five patients with cerebrovascular occlusive diseases (8 moyamoya diseases, 10 proximal internal carotid occlusions, and 2 sinus thromboses ) were studied with a 1.5-T MR unit. The MR digital subtraction angiography (MRDSA) was performed per 0.97 s continuously just after a bolus injection of 15 ml of gadolinium chelates up to 40 s in sagittal (covering hemisphere) or coronal planes. Subtraction images were generated at a workstation. We evaluated imaging quality and hemodynamic information of MRDSA in comparison with those of routine MR imaging, non-contrast MR angiography, and X-ray intra-arterial DSA. Major cerebral arteries, all of the venous sinuses, and most tributaries were clearly visualized with 2D MRDSA. Also, pure arterial phases were obtained in all cases. The MRDSA technique demonstrated prolonged circulation in sinus thromboses, distal patent lumen of proximal occlusion, and some collateral circulation. Such hemodynamic information was comparable to that of intra-arterial DSA. Two-dimensional thick-slice MRDSA with high temporal resolution has a unique ability to demonstrate cerebral hemodynamics equivalent to that of intra-arterial DSA and may play an important role for evaluation of cerebrovascular occlusive diseases. Received: 16 November 1999; Revised: 27 June 2000; Accepted: 29 June 2000     

Renal artery blood flow: quantification with breath-hold or respiratory triggered phase-contrast MR imaging

The aim of this study was to evaluate the validity and reproducibility of breath-hold and respiratory triggered phase-contrast (PC) MR imaging techniques in the measurement of renal artery blood flow. In 12 healthy subjects cardiac-gated PC flow measurements were obtained in the renal arteries using a breath-hold and a respiratory-triggered technique. The flow measurements were repeated in each renal artery separately. Comparison between the sum of flow measurements in the renal arteries and the difference in aortic flow measurements above and below the renal arteries served as an internal control. The flow measurements showed a good reproducibility both with the breath-hold (r = 0.92, p < 0.0001) and with the respiratory-triggered (r = 0.91, p < 0.0001) technique. The validity of both methods was good and there was no statistically significant difference. Reproducible quantitative measurements of renal artery blood flow are possible with respiratory controlled, cardiac-gated, PC MR imaging. Received: 12 February 1999; Revised: 8 February 2000; Accepted: 9 February 2000     

MR imaging of pituitary hyperplasia in a child with growth arrest and primary hypothyroidism

Magnetic resonance imaging of pituitary hyperplasia has been rarely described in children with primary hypothyroidism. We report a case of pituitary hyperplasia in a child presented with significant growth arrest and laboratory evidence of hypothyroidism. Magnetic resonance imaging revealed symmetrical pituitary enlargement simulating macroadenoma. After thyroid hormone replacement therapy, the child's height increased and pituitary enlargement regressed to normal. Awareness of MRI appearance of pituitary hyperplasia in children with laboratory evidence of hypothyroidism might avoid misdiagnosis for pituitary tumor, which may also manifest as growth disorder, obviating unnecessary surgery. Received: 4 March 1999; Revision received: 4 June 1999; Accepted: 7 June 1999     

A multipurpose phantom for quality assurance of contrast-enhanced MR imaging of the breast

A phantom consisting of four components was developed to simulate contrast-enhanced MR imaging of the breast. These components included the correlation between the signal intensity and the contrast medium concentration, the uniformity of signals within surface coils, artefacts due to opposed-phase imaging effects, spatial resolution and the acquisition of relevant signal-to-time curves. Repetitive measurements demonstrated an excellent reproduction of phantom imaging with a deviation in signal intensity of approximately 5 %. The presented phantom allows the optimization of examination protocols as well as the comparison of different examination techniques. Furthermore, it enables the routine quality monitoring of contrast-enhanced MR imaging of the breast. Received: 28 May 1998; Revised: 3 September 1998; Accepted: 14 October 1998     

MR imaging findings in granular cell tumor of the neurohypophysis: a difficult preoperative diagnosis

Granular cell tumor is a rare neoplasm arising within the neurohypophysis. We describe the MR imaging findings in two symptomatic patients. In one patient with history of panhypopituitarism, MR images showed a large sellar and suprasellar mass. The other patient presented with acute loss of vision in her left eye, and MR images showed a suprasellar mass with compression of the optic chiasm. Received: 18 November 1999; Revised: 5 April 2000; Accepted: 10 April 2000     

Technical advances in ultrasound and MR imaging of carpal tunnel syndrome

The aim of this study was to compare the latest ultrasound-array technology to a conventional “high-resolution” transducer, modified MRI technique, and nerve conduction studies (NCS), in the diagnosis of carpal tunnel syndrome (CTS). In 19 normal wrists and 15 wrists with CTS, US with two different transducers was performed: a conventional linear-array transducer (LA) and a newly developed Multi-D linear-array transducer (MDA) were used. The US images were evaluated determining the swelling and the flattening ratios of the median nerve and correlated to respective findings in MRI (1.5 T) and to NCS. The NCS confirmed CTS in all 15 wrists. Measures of median nerve compression (swelling and flattening ratios) were significantly different in patients with CTS and controls (p < 0.01) with both types of US transducers and MRI. The MDA yielded higher correlation to MRI than the LA. Using critical values of 1.3 for the swelling and 3.4 for the flattening ratio, MRI, and US with the MDA yielded a sensitivity of 100 % each. Modern imaging modalities allow for an exact diagnosis of CTS even in cases with only slight median nerve pathology. Received: 24 June 1999; Revised: 8 October 1999; Accepted: 25 February 2000