Editing Prostate Cancer: Diagnosis and evaluation (section)

====== <span style="color:#ff0000">Imaging sequences</span> ======
* Sequences relevant for prostate imaging
**T1-weighted imaging (T1WI)
**T2-weighted imaging (T2WI)
**Diffusion weighted imaging (DWI) with apparent diffusion coefficient (ADC) maps
**Dynamic contrast enhanced (DCE) imaging
**Magnetic resonance spectroscopic imaging (MRSI)
*Multi-parametric (mpMRI) is the combination of multiple MRI sequences
*'''<span style="color:#ff0000">In prostate cancer, the primary diagnostic parameters are (2):</span>[https://pubmed.ncbi.nlm.nih.gov/31392526/]'''
**'''<span style="color:#ff0000">T2WI</span>'''
**'''<span style="color:#ff0000">DWI with ADC maps</span>'''
* '''<span style="color:#ff0000">T2WI</span>'''
** Captures the movement of protons in the xy-axis (transverse)
** '''<span style="color:#ff0000">Primary uses (3):</span>'''
**#'''<span style="color:#ff0000">Visualization of zonal and anatomical features of the prostate.</span>'''
**#*See [https://www.researchgate.net/figure/Zonal-prostate-anatomy-on-axial-T2-weighted-MRI-image-peripheral-zone-PZ-and_fig1_346570342 Figure]
**#'''<span style="color:#ff0000">Optimal sequence in establishing the anatomic relation of the tumor with critical structures, such as the prostatic capsule and neurovascular bundles</span>'''.[https://pubmed.ncbi.nlm.nih.gov/26594835/]
**#'''<span style="color:#ff0000">Optimal sequence to evaluate lesions in the transition zone[https://pubmed.ncbi.nlm.nih.gov/31392526/]</span>'''
** '''<span style="color:#ff0000">Signal intensity</span>''' 
***'''<span style="color:#ff0000">High intensity</span>'''
****'''<span style="color:#ff0000">Fluids (CSF, urine)</span>'''
****'''<span style="color:#ff0000">Fat</span>'''
****'''<span style="color:#ff0000">Normal peripheral zone (due to its high water content)</span>'''
****'''<span style="color:#ff0000">Seminal vesicles</span>'''
***'''Intermediate intensity'''
****'''Central zone'''
*****Clinical implication: differential diagnosis of intermediate/low intensity lesions on T2 at the base of prostate and paramedian includes central zone that is being pushed out by BPH nodules of transition zone or cancer
***'''<span style="color:#ff0000">Low intensity (7): </span><span style="color:#0000ff">CHAPPSS</span>'''
***#'''<span style="color:#ff0000">Prostate </span><span style="color:#0000ff">C</span><span style="color:#ff0000">ancer</span>'''
***#*As 70% of all prostate cancers occur within the peripheral zone, the tissue characteristics allow for T2WI to detect a significant number of tumors in this zone
***#*
***#'''<span style="color:#0000ff">H</span><span style="color:#ff0000">emorrhage</span>'''
***#*Post-biopsy hemorrhage can interfere with tumor detection[https://pubmed.ncbi.nlm.nih.gov/26594835/], since areas of hemorrhage appear similar to cancer on T2WI
***#**If obtaining prostate MRI post-biopsy, a delay of 6-8 weeks after biopsy is recommended; but even with this delay, significant hemorrhage may be discovered, and, if present, the examination should be rescheduled[https://pubmed.ncbi.nlm.nih.gov/26594835/]
***#*Can be distinguished from cancer with T1WI (hemorrhage has high intensity on T1WI, cancer has low intensity on T2WI)
***#'''<span style="color:#0000ff">A</span><span style="color:#ff0000">trophy</span>'''
***#'''<span style="color:#0000ff">P</span><span style="color:#ff0000">rostatitis</span>'''
***#'''<span style="color:#0000ff">P</span><span style="color:#ff0000">ost-treatment changes</span>'''
***#'''<span style="color:#0000ff">S</span><span style="color:#ff0000">cars</span>'''
***#'''<span style="color:#0000ff">S</span><span style="color:#ff0000">tromal hyperplasia i.e. benign prostatic hyperplasia (BPH)</span>'''
***#*'''Clinical implication: On T2WI, BPH nodules can be difficult to distinguish from cancer'''
**Lesion shape
***Wedge-shaped/linear lesions are more likely benign 
* '''<span style="color:#ff0000">Diffusion weighted imaging (DWI)</span>'''
** '''Measures the diffusion of water protons within tissue'''
***'''In normal water-rich glandular tissue, protons are mobile'''
***'''In densely packed water-poor tissue such as that found in tumors, protons have restricted movement.'''
**Images are acquired by sequentially applying multiple magnetic field gradients, known as b-values, to calculate ADC values and construct ADC maps. 
***b-value is a factor that reflects the strength and timing of the gradients used to generate diffusion-weighted images. The higher the ''b''-value, the stronger the diffusion effects.
****Typical ''b''-values available on modern MRI scanners range from 0 to about 4000 s/mm²[https://mriquestions.com/what-is-the-b-value.html]
***ADC values are calculated by the software and displayed as a parametric map reflecting the degree of diffusion of water molecules through different tissues.
****Different b-values will produce different ADC maps
****In general, ADC values decrease when b-values increase above 1000 s/mm²[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4730971/]
**'''<span style="color:#ff0000">Primary use:</span>'''
***'''<span style="color:#ff0000">Optimal sequence to evaluate lesions in the peripheral zone[https://pubmed.ncbi.nlm.nih.gov/31392526/]</span>'''
**'''<span style="color:#ff0000">Signal intensity</span>'''
***'''<span style="color:#ff0000">ADC maps</span>'''
****'''Intermediate intensity'''
*****'''Normal glandular prostate tissue allows unrestricted free water movement'''
****'''<span style="color:#ff0000">Low intensity</span>'''
*****'''<span style="color:#ff0000">Prostate cancer</span>[https://pubmed.ncbi.nlm.nih.gov/23878284/]'''
******'''Appears as high signal intensity focus on high b-value images'''
*******Image with highest b-value (lowest ADC) likely to be most useful
******'''<span style="color:#ff0000">Tumors with the higher restriction (low ADC values) tend to be higher grade</span>'''
*'''<span style="color:#ff0000">T1WI</span>'''
** Captures the movement of protons in the z-axis
** '''<span style="color:#ff0000">Primary uses (2):</span>'''
**#'''<span style="color:#ff0000">Optimal sequence to identify areas of hemorrhage within the prostate</span>'''
**#'''Often used to look at normal anatomical details.'''
** '''<span style="color:#ff0000">Signal intensity</span>'''
***'''<span style="color:#ff0000">High intensity</span>'''
****'''<span style="color:#ff0000">Hemorrhage/blood has high signal intensity on T1</span>, against a homogenous low signal background.'''
****'''<span style="color:#ff0000">Fat</span>'''
***'''<span style="color:#ff0000">Low intensity'''
****'''<span style="color:#ff0000">Fluids (CSF, urine)</span>'''
****'''<span style="color:#ff0000">Prostate cancer'''
* '''<span style="color:#ff0000">Dynamic contrast enhancement (DCE)</span>'''
** A series of T1WI obtained before, during, and after the injection of intravenous gadolinium-based contrast media
**'''<span style="color:#ff0000">Primary use (1):</span>'''
***'''<span style="color:#ff0000">Measures the vascularity of prostate tissue</span>'''.
**** '''Focal early hyperenhancement is suggestive of a malignancy'''
*****Tumors have increased vascularity due to neo-angiogenesis and, therefore, take up the contrast agent more rapidly than normal tissue. Moreover, this contrast washes out of tumor regions quickly leading to a steep wash-in-wash-out enhancement curve.
*****There is considerable overlap of with benign conditions, such as benign prostatic hyperplasia and prostatitis.
******DCE MRI is most helpful when the T2W MRI and DWI are equivocal.
*******In these cases, strong early enhancement or rapid washout of contrast media from the lesion increases the suspicion that the lesion is a clinically significant malignancy. 
****Very useful in detecting sites of recurrent prostate cancer after prostatectomy or radiation therapy where focal enhancement may indicate a site of focal recurrence
* '''<span style="color:#ff0000">Magnetic resonance spectroscopic imaging (MRSI)</span>'''
** '''Uses the relative concentration of cellular metabolites in the prostate, specifically citrate and choline, to detect prostate cancer.'''
*** '''Citrate is a marker of normal prostatic tissue, whereas high levels of choline can be found in cancerous cells owing to increased cell turnover, which, in turn, leads to an increased choline-to-citrate ratio in patients with prostate cancer'''
** '''<span style="color:#ff0000">When combined with T2WI, MRSI has been found to have the highest sensitivity of all MRI sequences (92%) in detecting prostate cancer.</span>'''
** While MRSI is a promising imaging sequence, it requires an extra 10 to 15 minutes of examination time. Also, for this phase an endorectal coil (see below) is mandatory at 1.5T and optional at 3T. For these reasons, MRSI is less commonly performed than other mpMRI sequences in prostate MRI studies.
* '''Bi-parametric MRI (bpMRI)'''
** '''Combination of only non-contrast T2WI and DWI (with ADC maps) series''' 
**Advantages[https://pubmed.ncbi.nlm.nih.gov/26594835/]
***Can be performed without an endorectal coil
***Can be performed intravenous access and contrast administration
***Fewer sequences reduces time/costs to complete study
****Requires less than half the in-bore magnet time to perform compared with the complete mpMRI
**Disadvantages
***Fewer imaging sequences which may limit adequate interpretation
**'''No significant difference in sensitivity or specificity compared to mpMRI'''
***Systematic review and meta-analysis (2018)
****20 studies involving 2142 patients
****Results
*****No significant difference in pooled sensitivity and specificity
******Sensitivity: 0.74 (95% CI, 0.66–0.81) bpMRI vs. 0.76 (95% CI, 0.69–0.82) mpMRI
******Specificity: 0.90 (95% CI, 0.86–0.93) bpMRI vs. 0.89 (95% CI, 0.85–0.93) mpMRI
****[https://pubmed.ncbi.nlm.nih.gov/30240296/ Woo, Sungmin, et al.] "Head-to-head comparison between biparametric and multiparametric MRI for the diagnosis of prostate cancer: a systematic review and meta-analysis." ''American Journal of Roentgenology'' (2018): W226-W241.