Continuous arterial spin-labeling perfusion magnetic resonance imaging of the human testis1

Update on state-of-the-art for arterial spin labeling (ASL) human perfusion imaging outside of the brain

This review article provides an overview of developments for arterial spin labeling (ASL) perfusion imaging in the body (i.e., outside of the brain). It is part of a series of review/recommendation papers from the International Society for Magnetic Resonance in Medicine (ISMRM) Perfusion Study Group. In this review, we focus on specific challenges and developments tailored for ASL in a variety of body locations. After presenting common challenges, organ-specific reviews of challenges and developments are presented, including kidneys, lungs, heart (myocardium), placenta, eye (retina), liver, pancreas, and muscle, which are regions that have seen the most developments outside of the brain. Summaries and recommendations of acquisition parameters (when appropriate) are provided for each organ. We then explore the possibilities for wider adoption of body ASL based on large standardization efforts, as well as the potential opportunities based on recent advances in high/low-field systems and machine-learning. This review seeks to provide an overview of the current state-of-the-art of ASL for applications in the body, highlighting ongoing challenges and solutions that aim to enable more widespread use of the technique in clinical practice.

Dynamic contrast-enhanced subtraction MRI for characterizing intratesticular mass lesions

OBJECTIVE

The objective of our study was to analyze the enhancement patterns of various intratesticular mass lesions at dynamic contrast-enhanced subtraction MRI and assess the value of the technique in distinguishing between benign and malignant lesions.

MATERIALS AND METHODS

We retrospectively evaluated the records and images of 44 consecutive men (11 benign and 16 malignant intratesticular lesions) who presented to the department of urology with a variety of clinical symptoms and were referred for imaging. Dynamic contrast-enhanced subtraction MRI was performed using a 3D fast-field echo sequence after the administration of paramagnetic contrast medium. Patients were divided into three groups according to the final diagnosis: benign intratesticular lesions, malignant intratesticular lesions, and normal testes. The patterns of contrast enhancement of both the normal testes and the intratesticular lesions were evaluated. Time-signal intensity plots were created and classified according to shape: Type I presented a linear increase of contrast enhancement throughout the examination, type II showed an initial upstroke followed by either a plateau or a gradual increase in the late contrast-enhanced phase, and type III presented an initial upstroke followed by gradual washout of the contrast medium. The relative percentages of peak height, maximum time, and mean slope were also calculated.

RESULTS

Normal testes enhanced homogeneously with a type I curve. Most benign intratesticular lesions showed inhomogeneous or homogeneous contrast enhancement and a type II curve. Testicular carcinomas showed heterogeneous contrast enhancement with a type III curve. The relative percentages of maximum time to peak proved the most important discriminating factor in differentiating malignant from benign intratesticular masses (p < 0.001).

CONCLUSION

Dynamic contrast-enhanced MRI may be used to distinguish between benign and malignant intratesticular mass lesions.

MR imaging of testicular torsion: features of testicular hemorrhagic necrosis and clinical outcomes

PURPOSE

To determine whether emergency subtraction dynamic contrast-enhanced MR imaging (DCE-MRI) in combination with T2- and T2*-weighted imaging of the testis is useful in the evaluation of patients with testicular torsion.

MATERIALS AND METHODS

Fourteen patients with surgically proven testicular torsion were examined using preoperative emergency MRI, including T2-weighted, T2*-weighted, and DCE-MRI. The affected testis was examined histologically in eight patients who underwent orchiectomy, and by postoperative follow-up MRI in six patients who underwent orchiopexy. The diagnostic criteria for testicular torsion and detection of hemorrhagic necrosis in the affected testis in emergency MRI were decreased or no perfusion in DCE-MRI and a spotty and/or streaky pattern of low or very low signal intensity in T2- and T2*-weighted images. The intraoperative findings and clinical outcomes were also compared.

RESULTS

The histological findings and follow-up MR images revealed total or partial necrosis of the affected testis in 10 of the 14 patients. In the diagnosis of complete torsion, the sensitivities were 100% for DCE-MRI and 75% for T2- and T2*-weighted imaging. In the detection of testicular necrosis, T2- and T2*-weighted imaging showed the highest accuracy (100%), followed by 12-hour time from onset (93%), intraoperative findings (79%), and DCE-MRI (71%).

CONCLUSION

Emergency MRI can help diagnose testicular torsion and detect testicular necrosis when DCE-MRI is used in combination with T2- and T2*-weighted images.

Dynamic contrast-enhanced subtraction magnetic resonance imaging in diagnostics of testicular torsion

OBJECTIVES

To retrospectively correlate the magnetic resonance imaging (MRI) diagnosis with the surgical findings and/or clinical outcomes in patients presenting with an acute scrotum.

METHODS

From January 1997 to June 2004, 39 selected patients presenting with an acute scrotum underwent dynamic contrast-enhanced subtraction MRI as a 24-hour stand-by examination. The MRI diagnosis was based solely on the presence or absence of testicular contrast enhancement, without respect to the clinical history or physical examination findings.

RESULTS

Contrast enhancement of the affected and normal testes could be accurately compared in all cases. The MRI diagnosis was testicular torsion (no testicular contrast enhancement, n = 13), nonspecific (reduced to normal enhancement, n = 10), appendiceal torsion (n = 3), and epididymitis (n = 13). The surgical findings and/or subsequent clinical outcomes showed that MRI diagnosis of testicular torsion was accurate in all 13 cases. Furthermore, exploration revealed testicular torsion in 1 case with very little enhancement. The sensitivity and specificity of MRI in the diagnosis of testicular torsion was 93% (13 of 14) and 100% (25 of 25), respectively. Although MRI detected testicular perfusion, 5 of the 6 patients with clinical suspicion of intermittent torsion underwent surgical exploration.

CONCLUSIONS

MRI is a highly accurate imaging modality for the diagnosis of testicular torsion. However, it could not be used to rule out intermittent torsion and the clinical use of negative findings for an MRI torsion test was less than 100% specificity. Because this was a preliminary retrospective study, the true clinical value of MRI should be evaluated by prospective studies.

Magnetic resonance imaging of experimental testicular torsion

We investigated the feasibility of contrast enhanced (CE)-dynamic magnetic resonance imaging (MRI) for the detection of testicular torsion induced hypoperfusion in an experimental rat model. Adult Sprague-Dawley rats were subjected to unilateral testicular torsion of 360 or 720 degrees. After 1 h, the tail veins of the anaesthetized rats were cannulated and T2 -, diffusion-weighted and T1-weighted CE-dynamic MRI were subsequently performed by a 1.5 T MRI scanner. On apparent diffusion coefficient (ADC) images, the region of interest values of the ischaemic and control testes was compared. From CE-dynamic MR images, the maximal slopes of contrast enhancement were calculated and compared. In testicular torsion of 360 degrees, the maximal slope of contrast enhancement was 0.072%/s vs. 0.47%/s in the contralateral control testis (p < 0.001). A torsion of 720 degrees diminished the slope of contrast enhancement to 0.046%/s vs. 0.37%/s in the contralateral testis (p < 0.001). Diminished blood flow during torsion also followed in decreased ADC values in both 360 degrees (12.4% decrease; p < 0.05) and 720 degrees (10.8% decrease; p < 0.001) of torsion. Torsion of the testis causes ipsilateral hypoperfusion and decreased gadolinium uptake in a rat model that can be easily detected and quantified by CE-dynamic MRI. In diffusion-weighted MRI images, acute hypoperfusion results in a slight decrease of ADC values. Our results suggest that CE-dynamic MRI in combination with diffusion-weighted MRI can be used to detect compromised blood flow due to acute testicular torsion.

In vivo functional NMR imaging of resistance artery control

Arterial spin labeling (ASL) in combination with NMR imaging is an in vivo technique that quantifies tissue perfusion in absolute values (ml blood x min(-1) x g tissue(-1)) with high temporal (1-10 s) and spatial (0.1-3 mm) resolution. It uses the arterial water spins as endogenous freely diffusible markers of perfusion and, hence, is a totally noninvasive method. The technique has been successfully applied to quantify baseline perfusion in many organs, including the heart, in humans and animals, and results were validated by comparison with gold standards, PET and microspheres, respectively. Because of the high sampling rate of perfusion with ASL and the possibility that measurements could be obtained without harm over indefinite periods of time, the technique has the potential for use in functional investigations of microcirculation regulation and resistance artery control in vivo. We describe examples of the use of ASL to this end. With use of specific technological developments, ASL determination of perfusion can be coupled with simultaneous acquisitions of (1)H and (31)P NMR spectroscopy data. These protocols offer new possibilities whereby the microcirculatory control of cell oxygenation and high-energy phosphate metabolism can be explored.