Impact of patient comfort on diagnostic image quality during PET/MR exam: A quantitative survey study for clinical workflow management

Abstract Background PET/MR is transferring from a powerful scientific research tool to an imaging modality in clinical routine practice. Whole body PET/MR screening usually takes 30–50 minutes to finish, during which a few factors might induce patient discomfort and further cause degraded image quality. The aim of this report is to investigate the patients' perception of the imaging procedure and its correlation with image quality. Methods One hundred and twenty patients (63 males and 57 females, average age = 51.3 years, range 22–70 years) who had been diagnosed with cancer or had previous history of cancer were recruited and scanned with a simultaneous PET/MR system. A questionnaire was given to all patients retrospectively after the PET/MR scan, which has nine questions to assess patients' feeling of the scan on a Likert scale scoring system (1–5, 1 as most satisfied). All PET/MR images were also visually examined by two experts independently to evaluate the quality of the images. Six body locations were assessed and each location was evaluated also with a Likert scale scoring system (1–5, 5 as the best quality). Mann–Whitney Utest was used for statistical analysis to check if there is significant correlation between image quality and patient perceptions. Results With a total of 120 patients, 118 questionnaires were filled and returned for analysis. The patients’ characteristics were summarized in Table 4. The statistics of the patients’ perception in the questionnaire were illustrated in Tables 5–7. Statistical significant correlations were found between MR image quality and patients’ characteristics/perception. Conclusion Our results show that PET/MR scanning is generally safe and comfortable for most of the patients. Statistical analysis does not support the hypothesis that bad patient’s perception leads to degraded image quality.


| BACKGROUND
There has been a rapid growth of interest in whole body simultaneous PET/MR scan in the past few years. And PET/MR is transferring from a powerful scientific research tool to an imaging modality in clinical routine practice. 1 It has been demonstrated that PET/MR has a great potential in the area of neurology and oncology, such as Alzheimer's and Parkinson's Diseases (AD/PD), breast cancer, prostate cancer, colorectal carcinoma, melanoma, gynecological cancers, and brain tumors. [2][3][4][5][6][7] One of the major drawbacks of PET/MR imaging compared with PET/CT is the longer duration of scanning. Whole body PET/MR screening usually takes 30-50 minutes to finish, mainly due to the long scan time of MRI. 8 During the long process, a few factors might induce patient discomfort, such as acoustic noise, local heating from RF energy, and pressure from the MR surface coil.
Patients who are sensitive to these factors may disrupt the examination or move so much that image quality is severely degraded. Thus it is important to know the patients' perception of the imaging procedure.
A few previous studies have evaluated the tolerance of patients during imaging examinations. Sparrow et al. compared the patients' satisfaction and tolerance of MR and SPECT and found that more patients prefer MRI than SPECT with respect to tolerance and satisfaction during examinations. 9 By using Likert scale, Shortman et al.
compared PET/MR with PET/CT for the psychological burden before examinations, and found previous scanning experiences and communication with patients prior to and during PET/MRI improved patient satisfaction. 10 Similar findings were also found in a study conducted by Acuff et al. Furthermore, improved patient satisfaction may have a positive effect on imaging, because it can reduce involuntary motion. 11 PET/MR examination adopts all the technical challenges of a whole body MRI scan, including claustrophobia, physical discomfort, noise, scan duration, as well as the challenge of coping with emotions elicited during the scan such as fear/panic and isolation. In addition, subjects need to do preparations for PET imaging, include fasting, intake of water, administration of FDG, avoid motion, and unnecessary talking, this will further increase the stress and discomfort of the subjects during the examination. To the best of our knowledge, there has been no previous report on either patient comfort during whole body simultaneous PET/MR scans, or its correlation with diagnostic image quality. The aim of this paper is to report our survey results of the subjective patient response to varies factors during PET/MR scans and the impact of these factors on the final image quality. We hope this study can provide a guideline for designing a simultaneous PET/MR scan protocol.

2.A | Patients
One hundred and twenty patients (63 males and 57 females, average age = 51.3 years, range 22-70 years) who had been diagnosed with cancer or had the previous history of cancer were recruited and scanned with a simultaneous PET/MR system. This study was approved by the institutional review board (IRB)/Ethics Committee of Zhongshan Hospital. All patients gave written informed consent.
Inclusion and exclusion criteria were illustrated in Table 1.

2.E | Statistical analysis
Three categories of 14 factors in total were analyzed in this study and their correlation with image qualities was also studied. The first category includes patients' characteristics such as patients' gender, age, weight, and height. To explore the correlation between image quality and these factors, patients were divided into two groups based on each factor and median value for each factor was used as To further study the patients' tendency of giving scores, the patients were also grouped based on one simple criteria: whether he/she has gave a score of 4 or 5 to any of these nine questions.
Patients giving at least one score of 4 or 5 were put into group C while the rest were put into group D. And the average score of these two groups on each of the nine questions were calculated.
The difference of patents' characteristics (gender, weight, age, and height) between group C and D were also analyzed.
All the statistical analysis was performed in R-software environment(R Foundation for Statistical Computing, Vienna, Austria).

| RESULTS
With a total of 120 patients, 118 questionnaires were filled and returned for analysis. The patients' characteristics were summarized in

3.A | Patients' characteristics vs image quality
Correlation between MRI image quality and gender as well as body weight were studied. The statistical test revealed that gender has an impact on MR image quality on thorax and lower extremity (P = 0.025 and P = 0.038, respectively). The mean value of MRI image quality on thorax for man and woman are 3.81 and 3.73, respectively. And mean value of MRI image quality on lower extremity for man and woman are 4.62 and 4.20, respectively. These results revealed that MRI image quality in man on these two locations were better than woman. Moreover, body weight can also affect MR image quality on thorax (P = 0.037) that there is a significant difference in MR image quality between the patient group with body weight larger than 62 kg and those with body weight smaller than 62 kg (image quality score: 3.81 and 3.94, respectively). However, PET image quality and image fusion quality has no significant correlation with these factors.

Characteristics Statistics
Age (year) Median 55 The average image quality score for each body position in each group is showing in Table 8.  Table 11. Furthermore, no significant difference was observed between group C and D in terms of patient characteristics.

3.C | Scan time vs image quality
The mean scanning time of the patients are 52. 8  Among all the factors, the scores regarding heating and noise were the highest. Even earplugs were used during all the scans, the strong noise caused by MRI gradient pulsing is still a major factor affecting patient's comfort. A common way to mitigate the noise effect in a MRI scan is through using less gradient intensive sequences. However, this is not a practical option for PET/MR, because PET/MR scans are usually much longer than a regular MRI scan and compromise in gradient intensity would require even longer scan duration.
Better sound isolation and force balanced gradient design should be a more important concern in PET/MR systems than in MRI systems.
Patients' feeling on heating is another common complaint during PET/MR scans. The usage of a large surface coil covering most of the patient's body might be an important factor because it limits the heat dissipation. Another reason is that RF intensive MR sequences was included in our protocol resulting in more heat production.
In this study, image quality scores were obtained by a subjective metric, that is, evaluation from two radiologists. The human visual system is the gold standard in image quality evaluation. 14 16 and no reference image quality assessment (NR-IQA). [17][18][19][20][21] There are a few widely accepted FR-IQA techniques, such as Mean Squared Error (MSE), 22 Peak Signal-to-Noise Ratio (PSNR), 23 and Structural similarity Index (SSIM). 24 However, only NR-IQA is applicable for the purpose of evaluating medical images in this study. In general, NR-IQA is very challenging because no pristine image is available to compare with and the evaluation is highly application specific. 25 In our study, the primary factor that affects image quality is motion artifact. And motion artifact could have complex appearances because it is mixed with anatomical structures, which makes it difficult to quantify with standard quantitative metrics. Examples of MR motion artifact are shown in Figure 3 below. respiratory motion artifact was minimized. One example is curvilinear cold artifact which is commonly seen in PET/CT images because of respiration mismatch between PET images and CT attenuation correction.
According to the statistical test, heavy body weight has a negative effect on MR image quality. This finding is consistent with the situation in standalone MRI imaging. MR images of bigger patients usually suffer from worse signal to noise ratio and it is more likely to have image artifacts when the subject is closer to the edge of the field of view due to the deterioration of B0/B1 field homogeneity and gradient linearity. Another possible reason is that a heavier patient might feel more constricted in the bore of the system considering the bore size of the PET/MR system is only 60 cm. Even though it is more technically challenging to make a wide bore PET/ MR system than a standalone MRI system due to the extra spaced taken by the PET ring, it would be helpful to extend the bore size for a better patient perception.
Our study also shows that there are some correlations between the questionnaire items and the MR image quality. Moreover, overall scan time is another important factor that could affect image quality. All patients in this study were scanned with head-in-first supine body position and scanned from bottom to top. This is designed to minimize the effect of the continuous bladder expanding. Thus head and neck is the last scan location for each patients and the data shows that its image quality could suffer from the long scan duration. This is a strong evidence that it is crucial to optimize the clinical work flow to minimize the scan time.

AUTHORS' CONTRIBUTI ONS
HCS created the design of the study and analysis and supervised the project. SGC created the design of the study collected and analyzed the data, and drafted the manuscript. HPC contributed to statistical analysis and manuscript revision. GYC, ZZ, CTY, and YYZ participated in the design of the study and analysis and contributed to the manuscript revision and editing. All authors read and approved the final manuscript.

CONSENT FOR PUBLICATION
All authors read the manuscript and consented for its publication.

CONFLI CT OF INTERESTS
The authors declare that they have no competing interests.

ETHICS APPROVAL AND CONSENT TO PARTICIPATE
All procedures performed in studies involving human tissue were in accordance with the ethical standards of the institutional and/or national research committee and with the principles of the 1964 Declaration of Helsinki and its later amendments or comparable ethical standards.