X-ray microtomosynthesis of unstained pathology tissue samples

In pathology protocols, a tissue block, such as one containing a mouse brain or a biopsy sample from a patient, can produce several hundred thin sections. Substantial time may be required to analyse all sections. In cases of uncertainty regarding which sections to focus on, noninvasive scout imaging of intact blocks can help in guiding the pathology procedure. The scouting step is ideally done in a time window of minutes without special sample preparation that may interfere with the pathology procedures. The challenge is to obtain some visibility of unstained tissue structures at sub‐10 µm resolution.

We explored a novel x‐ray tomosynthesis method as a way to maximise contrast‐to‐noise ratio, a determinant of tissue visibility. It provided a z‐stack of thousands of images at 7.3 μm resolution (10% contrast, half‐period of 68.5 line pairs/mm), in scans of 5‐15 minutes. When compared with micro‐CT scans, the straight‐line tomosynthesis scan did not need to rotate the sample, which allowed flat samples, such as paraffin blocks, to be kept as close as possible to the x‐ray source. Thus, given the same hardware, scan time and resolution, this mode maximised the photon flux density through the sample, which helped in maximising the contrast‐to‐noise ratio. The tradeoff of tomosynthesis is incomplete 3D information.

The microtomosynthesis scanner has scanned 110 unstained human and animal tissue samples as part of their respective pathology protocols. In all cases, the z‐stack of images showed tissue structures that guided sectioning or provided correlative structural information. We describe six examples that presented different levels of visibility of soft tissue structures. Additionally, in a set of coronary artery samples from an HIV patient donor, microtomosynthesis made a new discovery of isolated focal calcification in the internal elastic lamina of coronary wall, which was the onset of medial calcific sclerosis in the arteries.

Regional Ultrahigh-Resolution Rescan in a Clinical Whole-Body CT Scanner Using a Contact Detector Insert

Ultrahigh-resolution, low-dose rescans in a region of interest following a general screening computed tomography (CT) scan is motivated by the need to reduce invasive tissue biopsy procedures in cancer screening. We describe a new method to meet the conflicting demands of ultrahigh resolution, high-speed and ultralow-dose, and the first proof-of-concept experiment. With improving detector resolution, the limiting factor for the system resolution of whole-body CT scanners shifts to the penumbra of the source focal spot. The penumbra unsharpness is minimized by inserting flat-panel detector(s) that are in direct contact with the body. In the hybrid system, the detector insert and the CT detector acquire data simultaneously, whereby the standard CT images give the position and orientation of the detector insert(s) as needed for tomosynthesis reconstruction. Imaging tests were performed with a compact photon-counting detector insert on resolution targets of both high- and low-contrast as well as a mouse specimen, all inside a body phantom. Detector insert tomosynthesis provided twice the resolution of the CT scanner alone at the same dose concentration. The short 2-cm beam collimation of the tomosynthesis rescan gave an effective dose equivalent to 6% of an average CT scan in the chest or abdomen.

Optimization of a secondary VOI protocol for lung imaging in a clinical CT scanner

We present a solution to meet an unmet clinical need of an in-situ "close look" at a pulmonary nodule or at the margins of a pulmonary cyst revealed by a primary (screening) chest CT while the patient is still in the scanner. We first evaluated options available on current whole-body CT scanners for high resolution screening scans, including ROI reconstruction of the primary scan data and HRCT, but found them to have insufficient SNR in lung tissue or discontinuous slice coverage. Within the capabilities of current clinical CT systems, we opted for the solution of a secondary, volume-of-interest (VOI) protocol where the radiation dose is focused into a short-beam axial scan at the z position of interest, combined with a small-FOV reconstruction at the xy position of interest. The objective of this work was to design a VOI protocol that is optimized for targeted lung imaging in a clinical whole-body CT system. Using a chest phantom containing a lung-mimicking foam insert with a simulated cyst, we identified the appropriate scan mode and optimized both the scan and recon parameters. The VOI protocol yielded 3.2 times the texture amplitude-to-noise ratio in the lung-mimicking foam when compared to the standard chest CT, and 8.4 times the texture difference between the lung mimicking and reference foams. It improved details of the wall of the simulated cyst and better resolution in a line-pair insert. The Effective Dose of the secondary VOI protocol was 42% on average and up to 100% in the worst-case scenario of VOI positioning relative to the standard chest CT. The optimized protocol will be used to obtain detailed CT textures of pulmonary lesions, which are biomarkers for the type and stage of lung diseases.

Ophthalmoplegic migraine: reversible enhancement and thickening of the cisternal segment of the oculomotor nerve on contrast-enhanced MR images

BACKGROUND AND PURPOSE

Ophthalmoplegic migraine is a rare condition characterized by the association of headaches and an oculomotor nerve palsy. We report six patients with typical clinical features of this disorder in whom enhancement of the cisternal segment of the oculomotor nerve developed during the acute phase, followed by resolution of enhancement over several weeks as the symptoms resolved.

METHODS

Six patients, ages 3 to 27 years, underwent MR imaging during the acute phase of ophthalmoplegic migraine and at the time of recovery several weeks later. The MR studies, performed on a 1.5-T MR unit, included noncontrast and contrast-enhanced axial and coronal T1-weighted sequences. Sagittal images were obtained in two patients, with and without contrast enhancement.

RESULTS

Enhancement of the cisternal segment of the oculomotor nerve was seen in all patients at initial presentation. Contrast-enhanced studies also showed focal thickening at the exit of the nerve in the interpeduncular cistern in five of six patients. No patient had enhancement of the cavernous sinus or adjacent dura. Enhancement was almost completely resolved on follow-up studies 7 to 9 weeks later.

CONCLUSION

Our findings confirm an intrinsic transient abnormality in the cisternal segment of the third nerve in patients with a typical clinical presentation of ophthalmoplegic migraine.