Effect of a Prescan Patient-Radiologist Encounter on Functional MR Image Quality

Assessment of Contrast-to-Noise Ratio

We assessed fMRI scan quality by first analyzing time-series data and conducting a preliminary study to ascertain that this would be an adequate approach. From the data base of all clinical fMRIs performed at our institution between August 23, 2005, and October 14, 2009, we selected all 41 patients who also had a confirmatory procedure for language lateralization, such as a Wada test. For head fMRI time-series data, gross motions of the head may appear as superimposed spikes. Such outliers were defined as any time point more than 3 SDs from the mean, and a total outlier score was computed as the total number of spikes from all voxels in a given sequence. Head motion is composed of linear displacement and rotation, each of which can occur along or around 3 axes. Such motion can be referenced to the centroid of a binary 3D image of the head, as computed from the center-of-mass and principal eigenvectors. These values were computed at each time point during the acquisition, and the variability of these time courses can serve as 1 measure of motion and can be quantified as the SD. Other measures are possible, and there is no criterion standard. We chose this approach of reviewing multiple possible motion parameters, rather than relying on just a few, to minimize any bias caused by the suboptimal choice of a single score.

Because a single noise score is desirable as a practical objective measure of fMRI scan quality, we computed single scores from time-series data on the basis of a weighted sum of 22 different factors. These factors included the overall SDs and the magnitude of mean head displacement and rotation; the correlation of mean head displacement and rotation with the task design; the correlation of mean head displacement and background intensity with the task design; and the magnitude of background gradients, the number of mean intensity outliers, and the fraction of activated voxels that are located within voxels just outside the parenchyma of the brain, where no physiologic activation should occur. These factors were weighted and summed so that a score of 0 reflected no motion; there was no upper limit. The weighting factors were chosen after qualitative review of all sequences from 41 patients in a preliminary study by 1 author (S.E.J.), comparing our subjective assessment of image quality with scores. We qualitatively recorded the noise scores as the following quartiles: 0–5 = excellent, 5–10 = adequate, 10–15 = marginal, and >15 = unacceptable. “Unacceptable” was defined as so poor that no conclusion could be drawn concerning localization of functional activation.

Prescan Study Design

Patients with epilepsy or brain tumor who were to undergo surgical resection were selected for study. To be included, patients had to be scanned during a routine clinical fMRI examination that included language assessment. Examinations were performed between July 2005 and March 2009. Non-English-speaking patients requiring translators were excluded; otherwise all consecutive examinations were included. The group without the prescan interview included the 41 patients described above, whose records were analyzed for the preliminary assessment of the contrast-to-noise-ratio methodology. Patient characteristics according to interview groups are displayed in Table 1.

The first group constituted 96 consecutive patients who did not have a prescan interview, which was the standard of care at that time. The subsequent group of 106 consecutive patients underwent a prescan interview, which is the new standard of care at our institution. The first cohort was analyzed retrospectively, while the second cohort was analyzed prospectively. All physician encounters were provided by the 11 members of the neuroradiology section staff at our institution, all of whom are coauthors. The interviews were roughly evenly distributed among the staff, who rotate daily through various clinical stations, 1 of which includes fMRI. All patients received our standard MR imaging safety questionnaire and the Edinburgh Inventory to determine handedness.²⁰ All patients in both groups also received instruction from the MR imaging technologist, both before and during imaging; the technician's instructions were the same regardless of whether the patient had also met with the physician. No other instruction was provided.

fMRI Scanning Protocol

All fMRI examinations were conducted on the same 3T Magnetom Trio magnet (Siemens, Erlangen, Germany) by using the same software. Each patient maintained audio contact with the control room by using pneumatic headphones as well as visual contact by using a mirror mounted on the head coil at a 45° angle, which permitted the patient to see a screen onto which a liquid crystal display projector could present required information. The patient provided feedback via a button box with 2 buttons placed at the patient's dominant hand.

The standard clinical examination at our institution for a preprocedural fMRI evaluation contains an initial anatomic sequence (T1-weighted 3D axial magnetization-prepared rapid acquisition of gradient echo; 120 0.94-mm-thick sections; TE/TR/TI/flip angle = 1.7 ms/900 ms/1900 ms/7°; 128 × 256 matrix; 256 × 256 mm FOV; receive bandwidth = 125.44 kHz.), followed by multiple functional paradigms with an echo-planar imaging sequence (160 volumes of 3.8-mm-thick axial sections, by using a prospective motion-controlled gradient recalled-echo echo-planar acquisition with TE/TR/flip angle = 29 ms/2000 ms/90°; matrix = 64 × 64; 256 × 256 mm FOV; receive bandwidth = 125 kHz). All tests were performed by using a block design comprising 4 cycles of 16 volumes of rest (32 seconds) alternating with 16 volumes of task (32 seconds). Occasionally, other additional clinical sequences were performed—for example fluid-attenuated inversion recovery, postcontrast T1, and diffusion tensor imaging.

At our institution, the standard clinical fMRI examination comprises 4 paradigms, 1 motor and 3 language tasks, all using the same block structure. The motor task consists of 4 cycles of bilateral finger tapping, each cycle containing 32 seconds of tapping followed by 32 seconds of rest. If clinically required, toe-curling and lip-pursing tasks are added to activate motor regions that might be more relevant to known pathology.

The 3 language tasks were covert word generation, a rhyming-decision task, and passive listening. Similar to the motor task, all language paradigms used 4 cycles, each containing 32 seconds of activation task followed by 32 seconds of control task. For covert word generation, patients were shown 2 different English letters displayed sequentially on a projection screen every 16 seconds during the activation phase, followed by 2 different nonsense symbols displayed sequentially every 16 seconds during the control phase. During activation phases, the patient was asked to covertly think of words beginning with the visualized letter, at a comfortable but rapid pace. During the control phase, the patient was asked to simply view the symbol and resist further mental activity. No patient response was obtained to verify compliance for this task for practical considerations. For the rhyming task, patients were shown word pairs during the activation phase every 4 seconds and were asked to press 1 button if the words rhymed or the other if they did not rhyme. Similarly, during the control phase, symbol pairs were shown and the patient was asked to press 1 button if the symbols matched or the other if they did not match. Patient responses were recorded, and a score was obtained. For the passive listening task, the patient listened through headphones to 4 cycles of audio segments from a familiar story, played forwards for 32 seconds followed by different segments played backwards for 32 seconds. Any task could be repeated at the discretion of the MR imaging technologist if they considered the quality of the results suboptimal.

The Prescan Patient-Physician Encounter

A 19-page flip folder was printed to guide the neuroradiologist in a brief standardized presentation that was used for all encounters, to achieve a relatively uniform patient-physician encounter. The purpose of the encounter was to reinforce the importance of minimizing motion and maximizing task cooperation. The overall aim of the presentation was to have the patient embrace their own study, to provide them with a sense of ownership and thereby maximize image quality. The encounter began with a brief education about fMRI and included images of fMRI scans obtained during common activities involving hearing or vision. This was followed by a short discussion of the general way in which images are acquired. MR imaging physics is complex and would not be easily or rapidly understood by many patients in this interview setting, but most can understand that the fMRI signal intensity is tiny compared with image noise and how signal-intensity quality can be degraded by either excessive movement or suboptimal task performance. Next, each assessment paradigm was discussed in detail with displayed examples and, if needed, rehearsed. Finally, the patient was shown examples of how fMRI images could be degraded by excessive motion and suboptimal participation (Fig 1), which often produce false-negative or false-positive activations. The clinical consequences of these false activations were emphasized in terms relative to the patient, with the neuroradiologist describing how a poor scan could lead the surgeon to resect either too much or too little tissue, resulting in suboptimal treatment.

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Fig 1.

Sample figures from the patient-physician encounter handbook demonstrating examples of fMRI image degradation due to excessive movement (left) and insufficient attention (right).

Statistical Analysis

The noise scores were compared between patients without a prescan interview (no interview group) and those with an interview (interview group). The datasets were automatically constructed from summary data files, which had been automatically composed from the image-analysis routine by using IDL v6.3 (ITT Visual Information Solutions, Boulder, Colorado). We compared the scores for each group in 2 ways, 1 sequence-based and 1 study (patient)-based. The sequence-based method grouped all sequences together, independent of any particular patient to which they belonged and produced a corresponding set of integer-valued noise scores. For the study-based method, the noise scores during each patient's entire study were averaged and then grouped to form a set of rational-valued noise scores. Differences between the no interview and interview groups were compared by using a Mann-Whitney U test. Noise scores were also dichotomized according to whether they were acceptable (score, ≤15) or unacceptable (score, >15), and the fraction of acceptable studies or sequences was calculated. This dichotomization reflected a common statement regarding the clinical impression of scan quality as either sufficient or insufficient for interpretation.