multiparametric mr imaging of the prostate

Sagittal plane can be used on patients with hip prosthesis in order to minimize image distortions and susceptibility artifacts. order to minimize image distortions and susceptibility ar[r]

Multiparametric MR Imaging of the prostate

HAI DUONG GENERAL HOSPITAL HAI DUONG GENERAL HOSPITAL

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Overview and Role of Radiology Technician

HAI DUONG GENERAL HOSPITAL HAI DUONG GENERAL HOSPITAL

Reporter: Nguyen

Reporter: Nguyen ManhManh CuongCuong

INTRODUTION INTRODUTION

Prostate cancer is the most common form of cancer

and it ranks second in mortality rate among the maley g

population worldwide Early diagnosis is the most effective method in dealing with and curing it.

Diagnostic methods include:

+ Digital rectal exam (DRE). + Prostate-specific antigen (PSA).

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The MRI Technologist plays a key role in the resultant examination quality, as preparation, positioning and communication with the patient, protocol set up and selection of the acquisition parameters are crucial for obtaining high quality, high resolution images of the prostate gland.

Sequence Rationale/investigated parameter

Technique Role in prostate cancer assessment with mpMRI Limitations CONTENT CONTENT

1 Request technicque for mpMRI prostate.

To provide resolution and high-contrast representation of the zonal anatomy of the prostate, as well as of periprostatic anatomy

• 2D turbo spin-echo with high spatial resolution: field of view 12–20 cm to cover the prostate and the seminal vesicles; slice thickness ≤ 3 mm with no gap; pixel size ≤ 0.7 mm

(phase)x ≤ 0.4 mm (frequency) • Sagittal, oblique transverse, oblique coronal (posterior prostate

• Detection and localisation: dominant sequence for assessing TZ findings • Locoregional staging: detection of • Nonspecific tumour appearance, overlapping with that of non-malignant conditions (e.g., inflammation or post-biopsy T2W (seminal vesicles,

neurovascular bundles, bladder, rectum, and the levator ani)

wall as anatomic landmark) extraprostatic extension or seminal vesicle invasion

changes) • Sensitive to motion artefacts given the prolonged acquisition time

Sequence Rationale/investig ated parameter

Technique Role in prostate cancer assessment with mpMRI

Limitations

To exploit restricted diffusion of water molecules as a marker of increased cellularity and

• Fat-saturated, free-breathing single-shot spin-echo echo-planar imaging

• At least twobvalues to

generate the ADC map (e.g., minimum 50–100 s/mm2,

maximum 800–1000 s/mm2);

extrapolated ultra-high b-values (≥ 1400 s/mm2) can also be used

Detection and localisation: • dominant sequence for assessing PZ findings

• secondary role in assessing category findings found by

• Sensitive to artefacts from air in the rectum and/or motion • Distortions • Relatively unstandardised technique, leading to limited reproducibility of the quantitative DWI neoplastic

reorganisation of normal glandular tissue

to generate the ADC map • Ultra-highbvalues can be

acquired to increase tumour conspicuity (not for the ADC map generation in less performing systems)

• Field of view 16–22 cm, slice thickness ≤ 4 mm without gap, pixel size ≤ 2.5 mm (phase and frequency) TR≤ 3000 ms TE

T2WI in the TZ analysis of ADC (no definite cut-off values) • Significant overlap of ADC values between benign conditions and tumours with different aggressiveness

CONTENT CONTENT Sequence Rationale/investigated

parameter

Technique Role in prostate cancer assessment with mpMRI

Limitations

To detect earlier and • Sequential acquisition of a T1 i ht d 2D 3D

• To upgrade bi fi di

• Variable h t tt

DCE

more intense contrast enhancement of cancer compared to normal prostatic tissue, as the expression of tumoural neoangiogenesis

T1-weighted 2D or 3D gradient-echo sequence with high temporal resolution (≤ 10 s, ideally ≤ 7 s, with TR < 5 ms and TE < 100 ms) Acquisition before, during and after contrast injection (at least 2 min) to detect early enhancement

• Field of view encompassing

ambiguous findings in the PZ

enhancement pattern of cancer,

overlapping with non-malignant conditions (e.g., inflammation or benign prostatic hyperplasia) • Longer acquisition time (> 2 min) to DCE

(denser, poorly formed vessels with increased capillary permeability)

Field of view encompassing the whole gland and seminal vesicles

• Slice thickness ≤ 3 mm without gap, and pixel size ≤ 2 mm (phase and frequency) • If possible fat-saturated or subtracted images

• Oblique transverse plane • Contrast injection rate 2–

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MRS

In prostate cancer, citrate levels fall (due to consumption of citrate to supply energy to proliferating cells), while choline levels increase (corresponding to increased cell membrane synthesis).

CONTENT CONTENT

2 Techique

Patient preparation and positioning

- The patient should not eat or drink any solid food for at least 4-6 hours in an attempt to reduce motion artifacts from bowel peristalsis

in an attempt to reduce motion artifacts from bowel peristalsis. - A full bladder should be avoided

- If possible, the patient should evacuate the rectum just prior to the examination in order to eliminate the presence of air The presence of air produces susceptibility artifacts and distortions, which mainly affect the DWI acquisition.p y , y q

- An antiperistaltic agent can be used to further reduce the motion artifacts from bowel peristalsis.

-CONTENT CONTENT

The patient needs to be as comfortable as possible to reduce any motion artifact + Prone - feet first position is an alternative

6 Imaging protocol and slice positioning

CONTENT CONTENT

Field strength: 1.5T – 3T:

+ 3T: increased SNR, higher image quality through improved spatial and temporal resolution, and/or reduced acquisition times

3 Technical Considerations

temporal resolution, and/or reduced acquisition times

+ 1.5T: An additional item to consider is patient safety and artifact generation Some medical implants may be incompatible at 3T for safety reasons In some cases, safety is not an issue but the implant may generate sufficient artifact to obscure or degrade the image In these cases, MR Imaging should be performed at 1.5T Coil selection: ERC and Body Coil Although many papers suggest the use of ERC at 1.5T scanners, high quality imaging can be obtained at both 1.5T and 3T without the use of an ERC

ERC

+ ERC: High resolution imaging.

SNR better than surface phased array coils.

The cost of the ERC, as well as the supplies and added time involved in the procedure, make the use of this method less practical

Deforms the shape of the gland. Cannot be used for whole pelvis Uncomfortable for patients.

CONTENT CONTENT

Imaging Parameters

T2W imaging:

Planes: sagittal coronal axial

Planes: sagittal, coronal, axial

Slice thickness and spacing: ≤3 mm with no gap between the slices

FOV: 16-22 cm, centered to the prostate gland

Spatial resolution: ≤0.7 mm (phase) and ≤0.4 mm (frequency), not interpolated.

Phase-encoding direction: R-L on axial and l d A P itt l

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Parallel imaging (PI): An acceleration factor of is most common.

Saturation bands: anterior sat bands should be used on the sagittal T2-w

Saturation bands: anterior sat bands should be used on the sagittal T2 w sequence to minimize motion artifacts from breathing.

Signal averages (NEX/NSA/ΝΑQ): high resolution T2-w imaging requires multiple signal averages Typically ≥3 signal averages should be used.

Receiver Bandwidth (rBW): high rBW should be used, an rBW of at least 27.7kHz should be selected.

Echo Spacing:as low as possible

TR:≥4000 msec

TR: ≥4000 msec

TE: 80-120 msec

ETL/Turbo factor: ≥16

Imaging Parameters

Diffusion-weighted imaging (DWI)

Plane(s): Axial Sagittal plane can be used on patients with hip prosthesis in order to minimize image distortions and susceptibility artifacts

order to minimize image distortions and susceptibility artifacts.

b-values: Diffusion-weighted acquisition should include low (50-100 s/mm2), high (800-1000 s/mm2) and very high (≥1400 s/mm2) b-values with

corresponding apparent diffusion coefficient (ADC) map.

Diffusion directions: Diffusion-sensitizing gradients in orthogonal directions should be used (trace or isotropic DWI).

Fat suppression: Fat saturation is necessary to eliminate chemical shift tif t

artifacts .

TR: ≥4000 ms

TE:as low as possible to reduce image distortions and improve SNR

Slice thickness and spacing:≤4 mm (ideally ≤3 mm) with no gap between the slices.

CONTENT CONTENT

Imaging Parameters

FOV: 16-32 cm (ideally 16-22 cm), centered to the prostate gland FOV may be larger than T2-w sequence in order to gain SNR.

Spatial resolution (pixel size): p (p ) ≤2.5 mm in phase and frequency encoding directions, p q y g ,

not interpolated.

Phase-encoding direction: A-P.

Parallel imaging: the use of PI technique is necessary to further reduce susceptibility artifacts, image distortion, and shot time.

Sat bands: anterior sat bands can be used to minimize the motion artifacts from

breathing Sat bands can also minimize wrap-around artifacts on patients with a large body habitus.

Signal averages (NEX/NSA/NAQ): Multiple signal averages should be used at high and very high b-values in order to gain SNR and maintain an adequate image quality.

Receiver Bandwidth (rBW): very high rBW should be used in order to minimize the

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Imaging Parameters

CONTENT CONTENT

Dynamic contrast-enhanced imaging (DCE):

Sequence:2D or 3D T1 GRE pulse sequence can be used However 3D T1

Sequence: 2D or 3D T1 GRE pulse sequence can be used However, 3D T1 GRE technique is preferred.

Plane(s): Axial Sagittal plane can be used on patients with hip prosthesis in order to minimize image distortions and susceptibility artifacts

Slice thickness and spacing: ≤3 mm with no gap

FOV: 16-22 cm, centered to the prostate gland

Spatial resolution: ≤2 mm in phase and frequency encoding directions, not interpolated

interpolated.

Temporal resolution: ≤15 sec A temporal resolution of ≤7 sec is suggested when quantitative assessment is required.

Parallel imaging: the use of parallel imaging technique is necessary to reduce the total acquisition time and to increase the temporal resolution.

Fat suppression: Fat suppression (or subtraction) is recommended when qualitative (visual) assessment is required Fat suppression is not necessary when quantitative assessment is needed.q

Flip Angle (FA): 15-20°

TR/TE: minimum

TA: ≥2 (ideally 4-5 min)

Flow rate: 2-3 ml/sec

Signal averages (NEX/NSA/NAQ): or Partial Fourier in order to increase the temporal resolution of DCE acquisition.

Receiver Bandwidth (rBW):very high rBW should be used in order to

Receiver Bandwidth (rBW): very high rBW should be used in order to minimize the echo spacing, which results in reduced image distortions and susceptibility artifacts Typically, an rBW of at least 62.5kHz should be selected.

Sat bands: Sat bands should not be used.

CONTENT CONTENT

12 MRS

CONCLUSION CONCLUSION

Multiparametric prostate MRI combines anatomical, functional and (occasionally) quantitative data in order to significantly increase the accuracy of the method in prostate cancer diagnosis.

The MRI Radiographer/Technologist occupies a very important role since the acquisition of a high-quality examination depends vastly on patient preparation and optimising the imaging protocol

optimising the imaging protocol.

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